1: #!/usr/bin/perl
2:
3: # The LearningOnline Network
4: # lonc - LON TCP-Client Domain-Socket-Server
5: # provides persistent TCP connections to the other servers in the network
6: # through multiplexed domain sockets
7: #
8: # $Id: lonc,v 1.53 2003/07/31 21:32:44 albertel Exp $
9: #
10: # Copyright Michigan State University Board of Trustees
11: #
12: # This file is part of the LearningOnline Network with CAPA (LON-CAPA).
13: #
14: # LON-CAPA is free software; you can redistribute it and/or modify
15: # it under the terms of the GNU General Public License as published by
16: # the Free Software Foundation; either version 2 of the License, or
17: # (at your option) any later version.
18: #
19: # LON-CAPA is distributed in the hope that it will be useful,
20: # but WITHOUT ANY WARRANTY; without even the implied warranty of
21: # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22: # GNU General Public License for more details.
23: #
24: # You should have received a copy of the GNU General Public License
25: # along with LON-CAPA; if not, write to the Free Software
26: # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
27: #
28: # /home/httpd/html/adm/gpl.txt
29: #
30: # http://www.lon-capa.org/
31: #
32: # PID in subdir logs/lonc.pid
33: # kill kills
34: # HUP restarts
35: # USR1 tries to open connections again
36:
37: # 6/4/99,6/5,6/7,6/8,6/9,6/10,6/11,6/12,7/14,7/19,
38: # 10/8,10/9,10/15,11/18,12/22,
39: # 2/8,7/25 Gerd Kortemeyer
40: # 12/05 Gerd Kortemeyer
41: # YEAR=2001
42: # 03/14/01,03/15,06/12,11/26,11/27,11/28 Gerd Kortemeyer
43: # YEAR=2002
44: # 2/19/02,02/22/02,02/25/02 Gerd Kortemeyer
45: # 3/07/02 Ron Fox
46: # based on nonforker from Perl Cookbook
47: # - server who multiplexes without forking
48:
49: use lib '/home/httpd/lib/perl/';
50: use LONCAPA::Configuration;
51:
52: use POSIX;
53: use IO::Socket;
54: use IO::Select;
55: use IO::File;
56: use Socket;
57: use Fcntl;
58: use Tie::RefHash;
59: use Crypt::IDEA;
60: #use Net::Ping;
61: use LWP::UserAgent();
62:
63: $status='';
64: $lastlog='';
65: $conserver='SHELL';
66: $DEBUG = 0; # Set to 1 for annoyingly complete logs.
67: $VERSION='$Revison$'; #' stupid emacs
68: $remoteVERSION;
69: # -------------------------------- Set signal handlers to record abnormal exits
70:
71: &status("Init exception handlers");
72: $SIG{QUIT}=\&catchexception;
73: $SIG{__DIE__}=\&catchexception;
74:
75: # ---------------------------------- Read loncapa_apache.conf and loncapa.conf
76: &status("Read loncapa.conf and loncapa_apache.conf");
77: my $perlvarref=LONCAPA::Configuration::read_conf('loncapa.conf');
78: my %perlvar=%{$perlvarref};
79: undef $perlvarref;
80:
81: # ----------------------------- Make sure this process is running from user=www
82: &status("Check user ID");
83: my $wwwid=getpwnam('www');
84: if ($wwwid!=$<) {
85: $emailto="$perlvar{'lonAdmEMail'},$perlvar{'lonSysEMail'}";
86: $subj="LON: $perlvar{'lonHostID'} User ID mismatch";
87: system("echo 'User ID mismatch. lonc must be run as user www.' |\
88: mailto $emailto -s '$subj' > /dev/null");
89: exit 1;
90: }
91:
92: # --------------------------------------------- Check if other instance running
93:
94: my $pidfile="$perlvar{'lonDaemons'}/logs/lonc.pid";
95:
96: if (-e $pidfile) {
97: my $lfh=IO::File->new("$pidfile");
98: my $pide=<$lfh>;
99: chomp($pide);
100: if (kill 0 => $pide) { die "already running"; }
101: }
102:
103: # ------------------------------------------------------------- Read hosts file
104:
105: open (CONFIG,"$perlvar{'lonTabDir'}/hosts.tab") || die "Can't read host file";
106:
107: while ($configline=<CONFIG>) {
108: my ($id,$domain,$role,$name,$ip)=split(/:/,$configline);
109: chomp($ip);
110: if ($ip) {
111: $hostip{$id}=$ip;
112: $hostname{$id}=$name;
113: }
114: }
115:
116: close(CONFIG);
117:
118: # -------------------------------------------------------- Routines for forking
119:
120: %children = (); # keys are current child process IDs,
121: # values are hosts
122: %childpid = (); # the other way around
123:
124: %childatt = (); # number of attempts to start server
125: # for ID
126:
127: $childmaxattempts=5;
128:
129: # ---------------------------------------------------- Fork once and dissociate
130: &status("Fork and dissociate");
131: $fpid=fork;
132: exit if $fpid;
133: die "Couldn't fork: $!" unless defined ($fpid);
134:
135: POSIX::setsid() or die "Can't start new session: $!";
136:
137: $conserver='PARENT';
138:
139: # ------------------------------------------------------- Write our PID on disk
140: &status("Write PID");
141: $execdir=$perlvar{'lonDaemons'};
142: open (PIDSAVE,">$execdir/logs/lonc.pid");
143: print PIDSAVE "$$\n";
144: close(PIDSAVE);
145: &logthis("<font color=red>CRITICAL: ---------- Starting ----------</font>");
146:
147: # ----------------------------- Ignore signals generated during initial startup
148: $SIG{HUP}=$SIG{USR1}='IGNORE';
149: # ------------------------------------------------------- Now we are on our own
150:
151: # Fork off our children, one for every server
152:
153: &status("Forking ...");
154:
155: foreach $thisserver (keys %hostip) {
156: #if (&online($hostname{$thisserver})) {
157: make_new_child($thisserver);
158: #}
159: }
160:
161: &logthis("Done starting initial servers");
162: # ----------------------------------------------------- Install signal handlers
163:
164:
165: $SIG{INT} = $SIG{TERM} = \&HUNTSMAN;
166: $SIG{HUP} = \&HUPSMAN;
167: $SIG{USR1} = \&USRMAN;
168:
169: # And maintain the population.
170: while (1) {
171: my $deadpid = wait; # Wait for the next child to die.
172: # See who died and start new one
173: # or a signal (e.g. USR1 for restart).
174: # if a signal, the wait will fail
175: # This is ordinarily detected by
176: # checking for the existence of the
177: # pid index inthe children hash since
178: # the return value from a failed wait is -1
179: # which is an impossible PID.
180: &status("Woke up");
181: my $skipping='';
182:
183: if(exists($children{$deadpid})) {
184:
185: $thisserver = $children{$deadpid}; # Look name of dead guy's peer.
186:
187: delete($children{$deadpid}); # Get rid of dead hash entry.
188:
189: if($childatt{$thisserver} < $childmaxattempts) {
190: $childatt{$thisserver}++;
191: &logthis(
192: "<font color=yellow>INFO: Trying to reconnect for $thisserver "
193: ."($childatt{$thisserver} of $childmaxattempts attempts)</font>");
194: make_new_child($thisserver);
195:
196: }
197: else {
198: $skipping .= $thisserver.' ';
199: }
200: if($skipping) {
201: &logthis("<font color=blue>WARNING: Skipped $skipping</font>");
202:
203: }
204: }
205:
206: }
207:
208:
209:
210: sub make_new_child {
211:
212: $newserver=shift;
213: my $pid;
214: my $sigset;
215: &logthis("Attempting to start child for server $newserver");
216: # block signal for fork
217: $sigset = POSIX::SigSet->new(SIGINT);
218: sigprocmask(SIG_BLOCK, $sigset)
219: or die "Can't block SIGINT for fork: $!\n";
220:
221: die "fork: $!" unless defined ($pid = fork);
222:
223: if ($pid) {
224: # Parent records the child's birth and returns.
225: sigprocmask(SIG_UNBLOCK, $sigset)
226: or die "Can't unblock SIGINT for fork: $!\n";
227: $children{$pid} = $newserver;
228: $childpid{$newserver} = $pid;
229: return;
230: } else {
231: $conserver=$newserver;
232: # Child can *not* return from this subroutine.
233: $SIG{INT} = 'DEFAULT'; # make SIGINT kill us as it did before
234: $SIG{USR1}= \&logstatus;
235:
236: # unblock signals
237: sigprocmask(SIG_UNBLOCK, $sigset)
238: or die "Can't unblock SIGINT for fork: $!\n";
239:
240: # ----------------------------- This is the modified main program of non-forker
241:
242: $port = "$perlvar{'lonSockDir'}/$conserver";
243:
244: unlink($port);
245:
246: # -------------------------------------------------------------- Open other end
247:
248: &openremote($conserver);
249: &logthis("<font color=green> Connection to $conserver open </font>");
250: # ----------------------------------------- We're online, send delayed messages
251: &status("Checking for delayed messages");
252:
253: my @allbuffered;
254: my $path="$perlvar{'lonSockDir'}/delayed";
255: opendir(DIRHANDLE,$path);
256: @allbuffered=grep /\.$conserver$/, readdir DIRHANDLE;
257: closedir(DIRHANDLE);
258: my $dfname;
259: foreach (sort @allbuffered) {
260: &status("Sending delayed: $_");
261: $dfname="$path/$_";
262: if($DEBUG) { &logthis('Sending '.$dfname); }
263: my $wcmd;
264: {
265: my $dfh=IO::File->new($dfname);
266: $cmd=<$dfh>;
267: }
268: chomp($cmd);
269: my $bcmd=$cmd;
270: if ($cmd =~ /^encrypt\:/) {
271: my $rcmd=$cmd;
272: $rcmd =~ s/^encrypt\://;
273: chomp($rcmd);
274: my $cmdlength=length($rcmd);
275: $rcmd.=" ";
276: my $encrequest='';
277: for (my $encidx=0;$encidx<=$cmdlength;$encidx+=8) {
278: $encrequest.=
279: unpack("H16",$cipher->encrypt(substr($rcmd,$encidx,8)));
280: }
281: $cmd="enc:$cmdlength:$encrequest\n";
282: }
283: $answer = londtransaction($remotesock, $cmd, 60);
284: chomp($answer);
285:
286: if (($answer ne '') && ($@!~/timeout/)) {
287: unlink("$dfname");
288: &logthis("Delayed $cmd: >$answer<");
289: &logperm("S:$conserver:$bcmd");
290: }
291: }
292: if($DEBUG) { &logthis("<font color=green> Delayed transactions sent"); }
293:
294: # ------------------------------------------------------- Listen to UNIX socket
295: &status("Opening socket");
296: unless (
297: $server = IO::Socket::UNIX->new(Local => $port,
298: Type => SOCK_STREAM,
299: Listen => 10 )
300: ) {
301: my $st=120+int(rand(240));
302: &logthis(
303: "<font color=blue>WARNING: ".
304: "Can't make server socket ($st secs): .. exiting</font>");
305: sleep($st);
306: exit;
307: };
308:
309: # -----------------------------------------------------------------------------
310:
311: &logthis("<font color=green>$conserver online</font>");
312:
313: # -----------------------------------------------------------------------------
314: # begin with empty buffers
315: %inbuffer = ();
316: %outbuffer = ();
317: %ready = ();
318: %servers = (); # To be compatible with make filevector. indexed by
319: # File ids, values are sockets.
320: # note that the accept socket is omitted.
321:
322: tie %ready, 'Tie::RefHash';
323:
324: # nonblock($server);
325: # $select = IO::Select->new($server);
326:
327: # Main loop: check reads/accepts, check writes, check ready to process
328:
329: status("Main loop $conserver");
330: while (1) {
331: my $client;
332: my $rv;
333: my $data;
334:
335: my $infdset; # bit vec of fd's to select on input.
336:
337: my $outfdset; # Bit vec of fd's to select on output.
338:
339:
340: $infdset = MakeFileVector(\%servers);
341: $outfdset= MakeFileVector(\%outbuffer);
342: vec($infdset, $server->fileno, 1) = 1;
343: if($DEBUG) {
344: &logthis("Adding ".$server->fileno.
345: " to input select vector (listner)".
346: unpack("b*",$infdset)."\n");
347: }
348: DoSelect(\$infdset, \$outfdset); # Wait for input.
349: if($DEBUG) {
350: &logthis("Doselect completed!");
351: &logthis("ins = ".unpack("b*",$infdset)."\n");
352: &logthis("outs= ".unpack("b*",$outfdset)."\n");
353:
354: }
355:
356: # Checkfor new connections:
357: if (vec($infdset, $server->fileno, 1)) {
358: if($DEBUG) {
359: &logthis("New connection established");
360: }
361: # accept a new connection
362: &status("Accept new connection: $conserver");
363: $client = $server->accept();
364: if($DEBUG) {
365: &logthis("New client fd = ".$client->fileno."\n");
366: }
367: $servers{$client->fileno} = $client;
368: nonblock($client);
369: $client->sockopt(SO_KEEPALIVE, 1);# Enable monitoring of
370: # connection liveness.
371: }
372: HandleInput($infdset, \%servers, \%inbuffer, \%outbuffer, \%ready);
373: HandleOutput($outfdset, \%servers, \%outbuffer, \%inbuffer,
374: \%ready);
375: # -------------------------------------------------------- Wow, connection lost
376:
377: }
378:
379: }
380: }
381:
382: # ------------------------------------------------------- End of make_new_child
383:
384:
385: #
386: # Make a vector of file descriptors to wait for in a select.
387: # parameters:
388: # \%fdhash -reference to a hash which has IO::Socket's as indices.
389: # We only care about the indices, not the values.
390: # A select vector is created from all indices of the hash.
391:
392: sub MakeFileVector
393: {
394: my $fdhash = shift;
395: my $selvar = "";
396:
397: foreach $socket (keys %$fdhash) {
398: if($DEBUG) {
399: &logthis("Adding ".$socket.
400: "to select vector. (client)\n");
401: }
402: vec($selvar, $socket, 1) = 1;
403: }
404: return $selvar;
405: }
406:
407:
408: #
409: # HandleOutput:
410: # Processes output on a buffered set of file descriptors which are
411: # ready to be read.
412: # Parameters:
413: # $selvector - Vector of file descriptors which are writable.
414: # \%sockets - Vector of socket references indexed by socket.
415: # \%buffers - Reference to a hash containing output buffers.
416: # Hashes are indexed by sockets. The file descriptors of some
417: # of those sockets will be present in $selvector.
418: # For each one of those, we will attempt to write the output
419: # buffer to the socket. Note that we will assume that
420: # the sockets are being run in non blocking mode.
421: # \%inbufs - Reference to hash containing input buffers.
422: # \%readys - Reference to hash containing flags for items with complete
423: # requests.
424: #
425: sub HandleOutput
426: {
427: my $selvector = shift;
428: my $sockets = shift;
429: my $buffers = shift;
430: my $inbufs = shift;
431: my $readys = shift;
432: my $sock;
433:
434: if($DEBUG) {
435: &logthis("HandleOutput entered\n");
436: }
437:
438: foreach $sock (keys %$sockets) {
439: my $socket = $sockets->{$sock};
440: if(vec($selvector, $sock, 1)) { # $socket is writable.
441: if($DEBUG) {
442: &logthis("Sending $buffers->{$sock} \n");
443: }
444: my $rv = $socket->send($buffers->{$sock}, 0);
445: $errno = $!;
446: unless ($buffers->{$sock} eq "con_lost\n") {
447: unless (defined $rv) { # Write failed... could be EINTR
448: unless ($errno == POSIX::EINTR) {
449: &logthis("Write failed on writable socket");
450: } # EINTR is not an error .. just retry.
451: next;
452: }
453: if( ($rv == length $buffers->{$sock}) ||
454: ($errno == POSIX::EWOULDBLOCK) ||
455: ($errno == POSIX::EAGAIN) || # same as above.
456: ($errno == POSIX::EINTR) || # signal during IO
457: ($errno == 0)) {
458: substr($buffers->{$sock}, 0, $rv)=""; # delete written part
459: delete $buffers->{$sock} unless length $buffers->{$sock};
460: } else {
461: # For some reason the write failed with an error code
462: # we didn't look for. Shutdown the socket.
463: &logthis("Unable to write data with ".$errno.": ".
464: "Dropping data: ".length($buffers->{$sock}).
465: ", $rv");
466: #
467: # kill off the buffers in the hash:
468:
469: delete $buffers->{$sock};
470: delete $inbufs->{$sock};
471: delete $readys->{$sock};
472:
473: close($socket); # Close the client socket.
474: next;
475: }
476: } else { # Kludgy way to mark lond connection lost.
477: &logthis(
478: "<font color=red>CRITICAL lond connection lost</font>");
479: status("Connection lost");
480: $remotesock->shutdown(2);
481: &logthis("Attempting to open a new connection");
482: &openremote($conserver);
483: }
484:
485: }
486: }
487:
488: }
489: #
490: # HandleInput - Deals with input on client sockets.
491: # Each socket has an associated input buffer.
492: # For each readable socket, the currently available
493: # data is appended to this buffer.
494: # If necessary, the buffer is created.
495: # On various failures, we may shutdown the client.
496: # Parameters:
497: # $selvec - Vector of readable sockets.
498: # \%sockets - Refers to the Hash of sockets indexed by sockets.
499: # Each of these may or may not have it's fd bit set
500: # in the $selvec.
501: # \%ibufs - Refers to the hash of input buffers indexed by socket.
502: # \%obufs - Hash of output buffers indexed by socket.
503: # \%ready - Hash of ready flags indicating the existence of a completed
504: # Request.
505: sub HandleInput
506: {
507:
508: # Marshall the parameters. Note that the hashes are actually
509: # references not values.
510:
511: my $selvec = shift;
512: my $sockets = shift;
513: my $ibufs = shift;
514: my $obufs = shift;
515: my $ready = shift;
516: my $sock;
517:
518: if($DEBUG) {
519: &logthis("Entered HandleInput\n");
520: }
521: foreach $sock (keys %$sockets) {
522: my $socket = $sockets->{$sock};
523: if(vec($selvec, $sock, 1)) { # Socket which is readable.
524:
525: # Attempt to read the data and do error management.
526: my $data = '';
527: my $rv = $socket->recv($data, POSIX::BUFSIZ, 0);
528: if($DEBUG) {
529: &logthis("Received $data from socket");
530: }
531: unless (defined($rv) && length $data) {
532:
533: # Read an end of file.. this is a disconnect from the peer.
534:
535: delete $sockets->{$sock};
536: delete $ibufs->{$sock};
537: delete $obufs->{$sock};
538: delete $ready->{$sock};
539:
540: status("Idle");
541: close $socket;
542: next;
543: }
544: # Append the read data to the input buffer. If the buffer
545: # now contains a \n the request is complete and we can
546: # mark this in the $ready hash (one request for each \n.)
547:
548: $ibufs->{$sock} .= $data;
549: while($ibufs->{$sock} =~ s/(.*\n)//) {
550: push(@{$ready->{$sock}}, $1);
551: }
552:
553: }
554: }
555: # Now handle any requests which are ready:
556:
557: foreach $client (keys %ready) {
558: handle($client);
559: }
560: }
561:
562: # DoSelect: does a select with no timeout. On signal (errno == EINTR),
563: # the select is retried until there are items in the returned
564: # vectors.
565: #
566: # Parameters:
567: # \$readvec - Reference to a vector of file descriptors to
568: # check for readability.
569: # \$writevec - Reference to a vector of file descriptors to check for
570: # writability.
571: # On exit, the referents are modified with vectors indicating which
572: # file handles are readable/writable.
573: #
574: sub DoSelect {
575: my $readvec = shift;
576: my $writevec= shift;
577: my $outs;
578: my $ins;
579:
580: while (1) {
581: my $nfds = select( $ins = $$readvec, $outs = $$writevec, undef, undef);
582: if($nfds) {
583: if($DEBUG) {
584: &logthis("select exited with ".$nfds." fds\n");
585: &logthis("ins = ".unpack("b*",$ins).
586: " readvec = ".unpack("b*",$$readvec)."\n");
587: &logthis("outs = ".unpack("b*",$outs).
588: " writevec = ".unpack("b*",$$writevec)."\n");
589: }
590: $$readvec = $ins;
591: $$writevec = $outs;
592: return;
593: } else {
594: if($DEBUG) {
595: &logthis("Select exited with no bits set in mask\n");
596: }
597: die "Select failed" unless $! == EINTR;
598: }
599: }
600: }
601:
602: # handle($socket) deals with all pending requests for $client
603: #
604: sub handle {
605: # requests are in $ready{$client}
606: # send output to $outbuffer{$client}
607: my $client = shift;
608: my $request;
609: foreach $request (@{$ready{$client}}) {
610: # ============================================================= Process request
611: # $request is the text of the request
612: # put text of reply into $outbuffer{$client}
613: # ------------------------------------------------------------ Is this the end?
614: chomp($request);
615: if($DEBUG) {
616: &logthis("<font color=green> Request $request processing starts</font>");
617: }
618: if ($request eq "close_connection_exit\n") {
619: &status("Request close connection");
620: &logthis(
621: "<font color=red>CRITICAL: Request Close Connection ... exiting</font>");
622: $remotesock->shutdown(2);
623: $server->close();
624: exit;
625: }
626: # -----------------------------------------------------------------------------
627: if ($request =~ /^encrypt\:/) {
628: my $cmd=$request;
629: $cmd =~ s/^encrypt\://;
630: chomp($cmd);
631: my $cmdlength=length($cmd);
632: $cmd.=" ";
633: my $encrequest='';
634: for (my $encidx=0;$encidx<=$cmdlength;$encidx+=8) {
635: $encrequest.=
636: unpack("H16",$cipher->encrypt(substr($cmd,$encidx,8)));
637: }
638: $request="enc:$cmdlength:$encrequest";
639: }
640: # --------------------------------------------------------------- Main exchange
641: $answer = londtransaction($remotesock, $request, 300);
642:
643: if($DEBUG) {
644: &logthis("<font color=green> Request data exchange complete");
645: }
646: if ($@=~/timeout/) {
647: $answer='';
648: &logthis(
649: "<font color=red>CRITICAL: Timeout: $request</font>");
650: }
651:
652:
653: if ($answer) {
654: if ($answer =~ /^enc/) {
655: my ($cmd,$cmdlength,$encinput)=split(/:/,$answer);
656: chomp($encinput);
657: $answer='';
658: for (my $encidx=0;$encidx<length($encinput);$encidx+=16) {
659: $answer.=$cipher->decrypt(
660: pack("H16",substr($encinput,$encidx,16))
661: );
662: }
663: $answer=substr($answer,0,$cmdlength);
664: $answer.="\n";
665: }
666: if($DEBUG) {
667: &logthis("sending $answer to client\n");
668: }
669: $outbuffer{$client} .= $answer;
670: } else {
671: $outbuffer{$client} .= "con_lost\n";
672: }
673:
674: &status("Completed: $request");
675: if($DEBUG) {
676: &logthis("<font color=green> Request processing complete</font>");
677: }
678: # ===================================================== Done processing request
679: }
680: delete $ready{$client};
681: # -------------------------------------------------------------- End non-forker
682: if($DEBUG) {
683: &logthis("<font color=green> requests for child handled</font>");
684: }
685: }
686: # ---------------------------------------------------------- End make_new_child
687:
688: # nonblock($socket) puts socket into nonblocking mode
689: sub nonblock {
690: my $socket = shift;
691: my $flags;
692:
693:
694: $flags = fcntl($socket, F_GETFL, 0)
695: or die "Can't get flags for socket: $!\n";
696: fcntl($socket, F_SETFL, $flags | O_NONBLOCK)
697: or die "Can't make socket nonblocking: $!\n";
698: }
699:
700:
701: sub openremote {
702: # ---------------------------------------------------- Client to network server
703:
704: my $conserver=shift;
705:
706: &status("Opening TCP $conserver");
707: my $st=120+int(rand(240)); # Sleep before opening:
708:
709: unless (
710: $remotesock = IO::Socket::INET->new(PeerAddr => $hostip{$conserver},
711: PeerPort => $perlvar{'londPort'},
712: Proto => "tcp",
713: Type => SOCK_STREAM)
714: ) {
715:
716: &logthis(
717: "<font color=blue>WARNING: Couldn't connect to $conserver ($st secs): </font>");
718: sleep($st);
719: exit;
720: };
721: # ----------------------------------------------------------------- Init dialog
722:
723: &logthis("<font color=green>INFO Connected to $conserver, initing</font>");
724: &status("Init dialogue: $conserver");
725:
726: $answer = londtransaction($remotesock, "init", 60);
727: chomp($answer);
728: $answer = londtransaction($remotesock, $answer, 60);
729: chomp($answer);
730:
731: if ($@=~/timeout/) {
732: &logthis("Timed out during init.. exiting");
733: exit;
734: }
735:
736: if ($answer ne 'ok') {
737: &logthis("Init reply: >$answer<");
738: my $st=120+int(rand(240));
739: &logthis("<font color=blue>WARNING: Init failed ($st secs)</font>");
740: sleep($st);
741: exit;
742: }
743:
744: $answer = londtransaction($remotesock,"sethost:$conserver",60);
745: chomp($answer);
746: if ( $answer ne 'ok') {
747: &logthis('<font color="blue">WARNING: unable to specify remote host'.
748: $answer.'</font>');
749: }
750:
751: $answer = londtransaction($remotesock,"version:$VERSION",60);
752: chomp($answer);
753: if ($answer =~ /^version:/) {
754: $remoteVERSION=(split(/:/,$answer))[1];
755: } else {
756: &logthis('<font color="blue">WARNING: request remote version failed :'.
757: $answer.': my version is :'.$VERSION.':</font>');
758: }
759:
760: sleep 5;
761: &status("Ponging $conserver");
762: $answer= londtransaction($remotesock,"pong",60);
763: chomp($answer);
764: if ($answer!~/^$conserver/) {
765: &logthis("Pong reply: >$answer<");
766: }
767: # ----------------------------------------------------------- Initialize cipher
768:
769: &status("Initialize cipher");
770: my $buildkey=londtransaction($remotesock,"ekey",60);
771: my $key=$conserver.$perlvar{'lonHostID'};
772: $key=~tr/a-z/A-Z/;
773: $key=~tr/G-P/0-9/;
774: $key=~tr/Q-Z/0-9/;
775: $key=$key.$buildkey.$key.$buildkey.$key.$buildkey;
776: $key=substr($key,0,32);
777: my $cipherkey=pack("H32",$key);
778: if ($cipher=new IDEA $cipherkey) {
779: &logthis("Secure connection initialized");
780: } else {
781: my $st=120+int(rand(240));
782: &logthis("<font color=blue>WARNING: ".
783: "Could not establish secure connection ($st secs)!</font>");
784: sleep($st);
785: exit;
786: }
787: &logthis("<font color=green> Remote open success </font>");
788: }
789:
790:
791:
792: # grabs exception and records it to log before exiting
793: sub catchexception {
794: my ($signal)=@_;
795: $SIG{QUIT}='DEFAULT';
796: $SIG{__DIE__}='DEFAULT';
797: chomp($signal);
798: &logthis("<font color=red>CRITICAL: "
799: ."ABNORMAL EXIT. Child $$ for server [$wasserver] died through "
800: ."\"$signal\" with parameter </font>");
801: die("Signal abend");
802: }
803:
804: # -------------------------------------- Routines to see if other box available
805:
806: #sub online {
807: # my $host=shift;
808: # &status("Pinging ".$host);
809: # my $p=Net::Ping->new("tcp",20);
810: # my $online=$p->ping("$host");
811: # $p->close();
812: # undef ($p);
813: # return $online;
814: #}
815:
816: sub connected {
817: my ($local,$remote)=@_;
818: &status("Checking connection $local to $remote");
819: $local=~s/\W//g;
820: $remote=~s/\W//g;
821:
822: unless ($hostname{$local}) { return 'local_unknown'; }
823: unless ($hostname{$remote}) { return 'remote_unknown'; }
824:
825: #unless (&online($hostname{$local})) { return 'local_offline'; }
826:
827: my $ua=new LWP::UserAgent;
828:
829: my $request=new HTTP::Request('GET',
830: "http://".$hostname{$local}.'/cgi-bin/ping.pl?'.$remote);
831:
832: my $response=$ua->request($request);
833:
834: unless ($response->is_success) { return 'local_error'; }
835:
836: my $reply=$response->content;
837: $reply=(split("\n",$reply))[0];
838: $reply=~s/\W//g;
839: if ($reply ne $remote) { return $reply; }
840: return 'ok';
841: }
842:
843:
844:
845: sub hangup {
846: foreach (keys %children) {
847: $wasserver=$children{$_};
848: &status("Closing $wasserver");
849: &logthis('Closing '.$wasserver.': '.&subreply('exit',$wasserver));
850: &status("Kill PID $_ for $wasserver");
851: kill ('INT',$_);
852: }
853: }
854:
855: sub HUNTSMAN { # signal handler for SIGINT
856: local($SIG{CHLD}) = 'IGNORE'; # we're going to kill our children
857: &hangup();
858: my $execdir=$perlvar{'lonDaemons'};
859: unlink("$execdir/logs/lonc.pid");
860: &logthis("<font color=red>CRITICAL: Shutting down</font>");
861: exit; # clean up with dignity
862: }
863:
864: sub HUPSMAN { # signal handler for SIGHUP
865: local($SIG{CHLD}) = 'IGNORE'; # we're going to kill our children
866: &hangup();
867: &logthis("<font color=red>CRITICAL: Restarting</font>");
868: my $execdir=$perlvar{'lonDaemons'};
869: unlink("$execdir/logs/lonc.pid");
870: exec("$execdir/lonc"); # here we go again
871: }
872:
873: sub checkchildren {
874: &initnewstatus();
875: &logstatus();
876: &logthis('Going to check on the children');
877: foreach (sort keys %children) {
878: sleep 1;
879: unless (kill 'USR1' => $_) {
880: &logthis ('<font color=red>CRITICAL: Child '.$_.' is dead</font>');
881: &logstatus($$.' is dead');
882: }
883: }
884: }
885:
886: sub USRMAN {
887: &logthis("USR1: Trying to establish connections again");
888: #
889: # It is really important not to just clear the childatt hash or we will
890: # lose all memory of the children. What we really want to do is this:
891: # For each index where childatt is >= $childmaxattempts
892: # Zero the associated counter and do a make_child for the host.
893: # Regardles, the childatt entry is zeroed:
894: my $host;
895: foreach $host (keys %childatt) {
896: if ($childatt{$host} >= $childmaxattempts) {
897: $childatt{$host} = 0;
898: &logthis("<font color=green>INFO: Restarting child for server: "
899: .$host."</font>\n");
900: make_new_child($host);
901: }
902: else {
903: $childatt{$host} = 0;
904: }
905: }
906: &checkchildren(); # See if any children are still dead...
907: }
908:
909: # -------------------------------------------------- Non-critical communication
910: sub subreply {
911: my ($cmd,$server)=@_;
912: my $answer='';
913: if ($server ne $perlvar{'lonHostID'}) {
914: my $peerfile="$perlvar{'lonSockDir'}/$server";
915: my $sclient=IO::Socket::UNIX->new(Peer =>"$peerfile",
916: Type => SOCK_STREAM,
917: Timeout => 10)
918: or return "con_lost";
919:
920:
921: $answer = londtransaction($sclient, $cmd, 10);
922:
923: if ((!$answer) || ($@=~/timeout/)) { $answer="con_lost"; }
924: $SIG{ALRM}='DEFAULT';
925: $SIG{__DIE__}=\&catchexception;
926: } else { $answer='self_reply'; }
927: return $answer;
928: }
929:
930: # --------------------------------------------------------------------- Logging
931:
932: sub logthis {
933: my $message=shift;
934: my $execdir=$perlvar{'lonDaemons'};
935: my $fh=IO::File->new(">>$execdir/logs/lonc.log");
936: my $now=time;
937: my $local=localtime($now);
938: $lastlog=$local.': '.$message;
939: print $fh "$local ($$) [$conserver] [$status]: $message\n";
940: }
941:
942: #-------------------------------------- londtransaction:
943: #
944: # Performs a transaction with lond with timeout support.
945: # result = londtransaction(socket,request,timeout)
946: #
947: sub londtransaction {
948: my ($socket, $request, $tmo) = @_;
949:
950: if($DEBUG) {
951: &logthis("londtransaction request: $request");
952: }
953:
954: # Set the signal handlers: ALRM for timeout and disble the others.
955:
956: $SIG{ALRM} = sub { die "timeout" };
957: $SIG{__DIE__} = 'DEFAULT';
958:
959: # Disable all but alarm so that only that can interupt the
960: # send /receive.
961: #
962: my $sigset = POSIX::SigSet->new(QUIT, USR1, HUP, INT, TERM);
963: my $priorsigs = POSIX::SigSet->new;
964: unless (defined sigprocmask(SIG_BLOCK, $sigset, $priorsigs)) {
965: &logthis("<font color=red> CRITICAL -- londtransaction ".
966: "failed to block signals </font>");
967: die "could not block signals in londtransaction";
968: }
969: $answer = '';
970: #
971: # Send request to lond.
972: #
973: eval {
974: alarm($tmo);
975: print $socket "$request\n";
976: alarm(0);
977: };
978: # If request didn't timeout, try for the response.
979: #
980:
981: if ($@!~/timeout/) {
982: eval {
983: alarm($tmo);
984: $answer = <$socket>;
985: if($DEBUG) {
986: &logthis("Received $answer in londtransaction");
987: }
988: alarm(0);
989: };
990: } else {
991: &logthis("lonc - suiciding on send Timeout");
992: die("lonc - suiciding on send Timeout");
993: }
994: if ($@ =~ /timeout/) {
995: &logthis("lonc - suiciding on read Timeout");
996: die("lonc - suiciding on read Timeout");
997: }
998: #
999: # Restore the initial sigmask set.
1000: #
1001: unless (defined sigprocmask(SIG_UNBLOCK, $priorsigs)) {
1002: &logthis("<font color=red> CRITICAL -- londtransaction ".
1003: "failed to re-enable signal processing. </font>");
1004: die "londtransaction failed to re-enable signals";
1005: }
1006: #
1007: # go back to the prior handler set.
1008: #
1009: $SIG{ALRM} = 'DEFAULT';
1010: $SIG{__DIE__} = \&cathcexception;
1011:
1012: # chomp $answer;
1013: if ($DEBUG) {
1014: &logthis("Returning $answer in londtransaction");
1015: }
1016: return $answer;
1017:
1018: }
1019:
1020: sub logperm {
1021: my $message=shift;
1022: my $execdir=$perlvar{'lonDaemons'};
1023: my $now=time;
1024: my $local=localtime($now);
1025: my $fh=IO::File->new(">>$execdir/logs/lonnet.perm.log");
1026: print $fh "$now:$message:$local\n";
1027: }
1028: # ------------------------------------------------------------------ Log status
1029:
1030: sub logstatus {
1031: my $docdir=$perlvar{'lonDocRoot'};
1032: my $fh=IO::File->new(">>$docdir/lon-status/loncstatus.txt");
1033: print $fh $$."\t".$conserver."\t".$status."\t".$lastlog."\n";
1034: }
1035:
1036: sub initnewstatus {
1037: my $docdir=$perlvar{'lonDocRoot'};
1038: my $fh=IO::File->new(">$docdir/lon-status/loncstatus.txt");
1039: my $now=time;
1040: my $local=localtime($now);
1041: print $fh "LONC status $local - parent $$\n\n";
1042: }
1043:
1044: # -------------------------------------------------------------- Status setting
1045:
1046: sub status {
1047: my $what=shift;
1048: my $now=time;
1049: my $local=localtime($now);
1050: $status=$local.': '.$what;
1051: $0='lonc: '.$what.' '.$local;
1052: }
1053:
1054:
1055:
1056: # ----------------------------------- POD (plain old documentation, CPAN style)
1057:
1058: =head1 NAME
1059:
1060: lonc - LON TCP-MySQL-Server Daemon for handling database requests.
1061:
1062: =head1 SYNOPSIS
1063:
1064: Usage: B<lonc>
1065:
1066: Should only be run as user=www. This is a command-line script which
1067: is invoked by B<loncron>. There is no expectation that a typical user
1068: will manually start B<lonc> from the command-line. (In other words,
1069: DO NOT START B<lonc> YOURSELF.)
1070:
1071: =head1 OVERVIEW
1072:
1073: =head2 Physical Overview
1074:
1075: =begin latex
1076:
1077: \begin{figure}
1078: \begin{center}
1079: \includegraphics[width=0.65\paperwidth,keepaspectratio]{LONCAPA_Network_Diagram}
1080: \end{center}
1081: \caption{\label{Overview_Of_Network}Overview of Network}
1082: \end{figure}
1083:
1084: =end latex
1085:
1086: Physically, the Network consists of relatively inexpensive
1087: upper-PC-class server machines which are linked through the commodity
1088: internet in a load-balancing, dynamically content-replicating and
1089: failover-secure way.
1090:
1091: All machines in the Network are connected with each other through
1092: two-way persistent TCP/IP connections. Clients (B<B>, B<F>, B<G> and
1093: B<H> in Fig. Overview of Network) connect to the servers via standard
1094: HTTP. There are two classes of servers, B<Library Servers> (B<A> and
1095: B<E> in Fig. Overview of Network) and B<Access Servers> (B<C>, B<D>,
1096: B<I> and B<J> in Fig. Overview of Network).
1097:
1098: B<Library Servers> X<library server> X<server, library> are used to
1099: store all personal records of a set of users, and are responsible for
1100: their initial authentication when a session is opened on any server in
1101: the Network. For Authors, Library Servers also hosts their
1102: construction area and the authoritative copy of the current and
1103: previous versions of every resource that was published by that
1104: author. Library servers can be used as backups to host sessions when
1105: all access servers in the Network are overloaded. Otherwise, for
1106: learners, access servers are used to host the sessions. Library
1107: servers need to have strong I/O capabilities.
1108:
1109: B<Access Servers> X<access server> X<server, access> provide LON-CAPA
1110: service to users, using the library servers as their data source. The
1111: network is designed so that the number of concurrent sessions can be
1112: increased over a wide range by simply adding additional access servers
1113: before having to add additional library servers. Preliminary tests
1114: showed that a library server could handle up to 10 access servers
1115: fully parallel. Access servers can generally be cheaper hardware then
1116: library servers require.
1117:
1118: The Network is divided into B<domains> X<domain>, which are logical
1119: boundaries between participating institutions. These domains can be
1120: used to limit the flow of personal user information across the
1121: network, set access privileges and enforce royalty schemes. LON-CAPA
1122: domains bear no relationship to any other domain, including domains
1123: used by the DNS system; LON-CAPA domains may be freely configured in
1124: any manner that suits your use pattern.
1125:
1126: =head2 Example Transactions
1127:
1128: Fig. Overview of Network also depicts examples for several kinds of
1129: transactions conducted across the Network.
1130:
1131: An instructor at client B<B> modifies and publishes a resource on her
1132: Home Server B<A>. Server B<A> has a record of all server machines
1133: currently subscribed to this resource, and replicates it to servers
1134: B<D> and B<I>. However, server B<D> is currently offline, so the
1135: update notification gets buffered on B<A> until B<D> comes online
1136: again. Servers B<C> and B<J> are currently not subscribed to this
1137: resource.
1138:
1139: Learners B<F> and B<G> have open sessions on server B<I>, and the new
1140: resource is immediately available to them.
1141:
1142: Learner B<H> tries to connect to server B<I> for a new session,
1143: however, the machine is not reachable, so he connects to another
1144: Access Server B<J> instead. This server currently does not have all
1145: necessary resources locally present to host learner B<H>, but
1146: subscribes to them and replicates them as they are accessed by B<H>.
1147:
1148: Learner B<H> solves a problem on server B<J>. Library Server B<E> is
1149: B<H>'s Home Server, so this information gets forwarded to B<E>, where
1150: the records of H are updated.
1151:
1152: =head2 lond, lonc, and lonnet
1153:
1154: =begin latex
1155:
1156: \begin{figure}
1157: \includegraphics[width=0.65\paperwidth,keepaspectratio]{LONCAPA_Network_Diagram2}
1158: \caption{\label{Overview_Of_Network_Communication}Overview of
1159: Network Communication} \end{figure}
1160:
1161: =end latex
1162:
1163: Fig. Overview of Network Communication elaborates on the details of
1164: this network infrastructure. It depicts three servers (B<A>, B<B> and
1165: B<C>) and a client who has a session on server B<C>.
1166:
1167: As B<C> accesses different resources in the system, different
1168: handlers, which are incorporated as modules into the child processes
1169: of the web server software, process these requests.
1170:
1171: Our current implementation uses C<mod_perl> inside of the Apache web
1172: server software. As an example, server B<C> currently has four active
1173: web server software child processes. The chain of handlers dealing
1174: with a certain resource is determined by both the server content
1175: resource area (see below) and the MIME type, which in turn is
1176: determined by the URL extension. For most URL structures, both an
1177: authentication handler and a content handler are registered.
1178:
1179: Handlers use a common library C<lonnet> X<lonnet> to interact with
1180: both locally present temporary session data and data across the server
1181: network. For example, lonnet provides routines for finding the home
1182: server of a user, finding the server with the lowest loadavg, sending
1183: simple command-reply sequences, and sending critical messages such as
1184: a homework completion, etc. For a non-critical message, the routines
1185: reply with a simple "connection lost" if the message could not be
1186: delivered. For critical messages, lonnet tries to re-establish
1187: connections, re-send the command, etc. If no valid reply could be
1188: received, it answers "connection deferred" and stores the message in
1189: buffer space to be sent at a later point in time. Also, failed
1190: critical messages are logged.
1191:
1192: The interface between C<lonnet> and the Network is established by a
1193: multiplexed UNIX domain socket, denoted B<DS> in Fig. Overview of
1194: Network Communication. The rationale behind this rather involved
1195: architecture is that httpd processes (Apache children) dynamically
1196: come and go on the timescale of minutes, based on workload and number
1197: of processed requests. Over the lifetime of an httpd child, however,
1198: it has to establish several hundred connections to several different
1199: servers in the Network.
1200:
1201: On the other hand, establishing a TCP/IP connection is resource
1202: consuming for both ends of the line, and to optimize this connectivity
1203: between different servers, connections in the Network are designed to
1204: be persistent on the timescale of months, until either end is
1205: rebooted. This mechanism will be elaborated on below.
1206:
1207: =begin latex
1208:
1209: \begin{figure}
1210: \begin{lyxcode}
1211: msul1:msu:library:zaphod.lite.msu.edu:35.8.63.51
1212:
1213: msua1:msu:access:agrajag.lite.msu.edu:35.8.63.68
1214:
1215: msul2:msu:library:frootmig.lite.msu.edu:35.8.63.69
1216:
1217: msua2:msu:access:bistromath.lite.msu.edu:35.8.63.67
1218:
1219: hubl14:hub:library:hubs128-pc-14.cl.msu.edu:35.8.116.34
1220:
1221: hubl15:hub:library:hubs128-pc-15.cl.msu.edu:35.8.116.35
1222:
1223: hubl16:hub:library:hubs128-pc-16.cl.msu.edu:35.8.116.36
1224:
1225: huba20:hub:access:hubs128-pc-20.cl.msu.edu:35.8.116.40
1226:
1227: huba21:hub:access:hubs128-pc-21.cl.msu.edu:35.8.116.41
1228:
1229: huba22:hub:access:hubs128-pc-22.cl.msu.edu:35.8.116.42
1230:
1231: huba23:hub:access:hubs128-pc-23.cl.msu.edu:35.8.116.43
1232:
1233: hubl25:other:library:hubs128-pc-25.cl.msu.edu:35.8.116.45
1234:
1235: huba27:other:access:hubs128-pc-27.cl.msu.edu:35.8.116.47
1236: \end{lyxcode}
1237:
1238: \caption{\label{Example_Of_hosts.tab}Example of Hosts Lookup table\texttt{/home/httpd/lonTabs/hosts.tab}}
1239: \end{figure}
1240:
1241: =end latex
1242:
1243: Establishing a connection to a UNIX domain socket is far less resource
1244: consuming than the establishing of a TCP/IP connection. C<lonc>
1245: X<lonc> is a proxy daemon that forks off a child for every server in
1246: the Network. Which servers are members of the Network is determined by
1247: a lookup table, such as the one in Fig. Examples of Hosts. In order,
1248: the entries denote an internal name for the server, the domain of the
1249: server, the type of the server, the host name and the IP address.
1250:
1251: The C<lonc> parent process maintains the population and listens for
1252: signals to restart or shutdown, as well as I<USR1>. Every child
1253: establishes a multiplexed UNIX domain socket for its server and opens
1254: a TCP/IP connection to the lond daemon (discussed below) on the remote
1255: machine, which it keeps alive. If the connection is interrupted, the
1256: child dies, whereupon the parent makes several attempts to fork
1257: another child for that server.
1258:
1259: When starting a new child (a new connection), first an init-sequence
1260: is carried out, which includes receiving the information from the
1261: remote C<lond> which is needed to establish the 128-bit encryption key
1262: - the key is different for every connection. Next, any buffered
1263: (delayed) messages for the server are sent.
1264:
1265: In normal operation, the child listens to the UNIX socket, forwards
1266: requests to the TCP connection, gets the reply from C<lond>, and sends
1267: it back to the UNIX socket. Also, C<lonc> takes care to the encryption
1268: and decryption of messages.
1269:
1270: C<lond> X<lond> is the remote end of the TCP/IP connection and acts as
1271: a remote command processor. It receives commands, executes them, and
1272: sends replies. In normal operation, a C<lonc> child is constantly
1273: connected to a dedicated C<lond> child on the remote server, and the
1274: same is true vice versa (two persistent connections per server
1275: combination).
1276:
1277: lond listens to a TCP/IP port (denoted B<P> in Fig. Overview of
1278: Network Communication) and forks off enough child processes to have
1279: one for each other server in the network plus two spare children. The
1280: parent process maintains the population and listens for signals to
1281: restart or shutdown. Client servers are authenticated by IP.
1282:
1283: When a new client server comes online, C<lond> sends a signal I<USR1>
1284: to lonc, whereupon C<lonc> tries again to reestablish all lost
1285: connections, even if it had given up on them before - a new client
1286: connecting could mean that that machine came online again after an
1287: interruption.
1288:
1289: The gray boxes in Fig. Overview of Network Communication denote the
1290: entities involved in an example transaction of the Network. The Client
1291: is logged into server B<C>, while server B<B> is her Home
1292: Server. Server B<C> can be an access server or a library server, while
1293: server B<B> is a library server. She submits a solution to a homework
1294: problem, which is processed by the appropriate handler for the MIME
1295: type "problem". Through C<lonnet>, the handler writes information
1296: about this transaction to the local session data. To make a permanent
1297: log entry, C<lonnet> establishes a connection to the UNIX domain
1298: socket for server B<B>. C<lonc> receives this command, encrypts it,
1299: and sends it through the persistent TCP/IP connection to the TCP/IP
1300: port of the remote C<lond>. C<lond> decrypts the command, executes it
1301: by writing to the permanent user data files of the client, and sends
1302: back a reply regarding the success of the operation. If the operation
1303: was unsuccessful, or the connection would have broken down, C<lonc>
1304: would write the command into a FIFO buffer stack to be sent again
1305: later. C<lonc> now sends a reply regarding the overall success of the
1306: operation to C<lonnet> via the UNIX domain port, which is eventually
1307: received back by the handler.
1308:
1309: =head2 Dynamic Resource Replication
1310:
1311: Since resources are assembled into higher order resources simply by
1312: reference, in principle it would be sufficient to retrieve them from
1313: the respective Home Servers of the authors. However, there are several
1314: problems with this simple approach: since the resource assembly
1315: mechanism is designed to facilitate content assembly from a large
1316: number of widely distributed sources, individual sessions would depend
1317: on a large number of machines and network connections to be available,
1318: thus be rather fragile. Also, frequently accessed resources could
1319: potentially drive individual machines in the network into overload
1320: situations.
1321:
1322: Finally, since most resources depend on content handlers on the Access
1323: Servers to be served to a client within the session context, the raw
1324: source would first have to be transferred across the Network from the
1325: respective Library Server to the Access Server, processed there, and
1326: then transferred on to the client.
1327:
1328: =begin latex
1329:
1330: \begin{figure}
1331: \includegraphics[width=0.75\paperwidth,keepaspectratio]{Dynamic_Replication_Request}
1332: \caption{\label{Dynamic_Replication}Dynamic Replication}
1333: \end{figure}
1334:
1335: =end latex
1336:
1337: To enable resource assembly in a reliable and scalable way, a dynamic
1338: resource replication scheme was developed. Fig. "Dynamic Replication"
1339: shows the details of this mechanism.
1340:
1341: Anytime a resource out of the resource space is requested, a handler
1342: routine is called which in turn calls the replication routine. As a
1343: first step, this routines determines whether or not the resource is
1344: currently in replication transfer (Step B<D1a>). During replication
1345: transfer, the incoming data is stored in a temporary file, and Step
1346: B<D1a> checks for the presence of that file. If transfer of a resource
1347: is actively going on, the controlling handler receives an error
1348: message, waits for a few seconds, and then calls the replication
1349: routine again. If the resource is still in transfer, the client will
1350: receive the message "Service currently not available".
1351:
1352: In the next step (Step B<D1b>), the replication routine checks if the
1353: URL is locally present. If it is, the replication routine returns OK
1354: to the controlling handler, which in turn passes the request on to the
1355: next handler in the chain.
1356:
1357: If the resource is not locally present, the Home Server of the
1358: resource author (as extracted from the URL) is determined (Step
1359: B<D2>). This is done by contacting all library servers in the author?s
1360: domain (as determined from the lookup table, see Fig. 1.1.2B). In Step
1361: B<D2b> a query is sent to the remote server whether or not it is the
1362: Home Server of the author (in our current implementation, an
1363: additional cache is used to store already identified Home Servers (not
1364: shown in the figure)). In Step B<D2c>, the remote server answers the
1365: query with True or False. If the Home Server was found, the routine
1366: continues, otherwise it contacts the next server (Step D2a). If no
1367: server could be found, a "File not Found" error message is issued. In
1368: our current implementation, in this step the Home Server is also
1369: written into a cache for faster access if resources by the same author
1370: are needed again (not shown in the figure).
1371:
1372: =begin latex
1373:
1374: \begin{figure}
1375: \includegraphics[width=0.75\paperwidth,keepaspectratio]{Dynamic_Replication_Change}
1376: \caption{\label{Dynamic_Replication_Change}Dynamic Replication: Change} \end{figure}
1377:
1378: =end latex
1379:
1380: In Step B<D3a>, the routine sends a subscribe command for the URL to
1381: the Home Server of the author. The Home Server first determines if the
1382: resource is present, and if the access privileges allow it to be
1383: copied to the requesting server (B<D3b>). If this is true, the
1384: requesting server is added to the list of subscribed servers for that
1385: resource (Step B<D3c>). The Home Server will reply with either OK or
1386: an error message, which is determined in Step D4. If the remote
1387: resource was not present, the error message "File not Found" will be
1388: passed on to the client, if the access was not allowed, the error
1389: message "Access Denied" is passed on. If the operation succeeded, the
1390: requesting server sends an HTTP request for the resource out of the
1391: C</raw> server content resource area of the Home Server.
1392:
1393: The Home Server will then check if the requesting server is part of
1394: the network, and if it is subscribed to the resource (Step B<D5b>). If
1395: it is, it will send the resource via HTTP to the requesting server
1396: without any content handlers processing it (Step B<D5c>). The
1397: requesting server will store the incoming data in a temporary data
1398: file (Step B<D5a>) - this is the file that Step B<D1a> checks for. If
1399: the transfer could not complete, and appropriate error message is sent
1400: to the client (Step B<D6>). Otherwise, the transferred temporary file
1401: is renamed as the actual resource, and the replication routine returns
1402: OK to the controlling handler (Step B<D7>).
1403:
1404: Fig. "Dynamic Replication: Change" depicts the process of modifying a
1405: resource. When an author publishes a new version of a resource, the
1406: Home Server will contact every server currently subscribed to the
1407: resource (Step B<U1>), as determined from the list of subscribed
1408: servers for the resource generated in Step B<D3c>. The subscribing
1409: servers will receive and acknowledge the update message (Step
1410: B<U1c>). The update mechanism finishes when the last subscribed server
1411: has been contacted (messages to unreachable servers are buffered).
1412:
1413: Each subscribing server will check if the resource in question had
1414: been accessed recently, that is, within a configurable amount of time
1415: (Step B<U2>).
1416:
1417: If the resource had not been accessed recently, the local copy of the
1418: resource is deleted (Step B<U3a>) and an unsubscribe command is sent
1419: to the Home Server (Step B<U3b>). The Home Server will check if the
1420: server had indeed originally subscribed to the resource (Step B<U3c>)
1421: and then delete the server from the list of subscribed servers for the
1422: resource (Step B<U3d>).
1423:
1424: If the resource had been accessed recently, the modified resource will
1425: be copied over using the same mechanism as in Step B<D5a> through
1426: B<D7>, which represents steps Steps B<U4a> through B<U6> in the
1427: replication figure.
1428:
1429: =head2 Load Balancing
1430:
1431: X<load balancing>C<lond> provides a function to query the server's current loadavg. As
1432: a configuration parameter, one can determine the value of loadavg,
1433: which is to be considered 100%, for example, 2.00.
1434:
1435: Access servers can have a list of spare access servers,
1436: C</home/httpd/lonTabs/spares.tab>, to offload sessions depending on
1437: own workload. This check happens is done by the login handler. It
1438: re-directs the login information and session to the least busy spare
1439: server if itself is overloaded. An additional round-robin IP scheme
1440: possible. See Fig. "Load Balancing Sample" for an example of a
1441: load-balancing scheme.
1442:
1443: =begin latex
1444:
1445: \begin{figure}
1446: \includegraphics[width=0.75\paperwidth,keepaspectratio]{Load_Balancing_Example}
1447: \caption{\label{Load_Balancing_Example}Load Balancing Example} \end{figure}
1448:
1449: =end latex
1450:
1451: =head1 DESCRIPTION
1452:
1453: Provides persistent TCP connections to the other servers in the network
1454: through multiplexed domain sockets
1455:
1456: B<lonc> forks off children processes that correspond to the other servers
1457: in the network. Management of these processes can be done at the
1458: parent process level or the child process level.
1459:
1460: After forking off the children, B<lonc> the B<parent> executes a main
1461: loop which simply waits for processes to exit. As a process exits, a
1462: new process managing a link to the same peer as the exiting process is
1463: created.
1464:
1465: B<logs/lonc.log> is the location of log messages.
1466:
1467: The process management is now explained in terms of linux shell commands,
1468: subroutines internal to this code, and signal assignments:
1469:
1470: =over 4
1471:
1472: =item *
1473:
1474: PID is stored in B<logs/lonc.pid>
1475:
1476: This is the process id number of the parent B<lonc> process.
1477:
1478: =item *
1479:
1480: SIGTERM and SIGINT
1481:
1482: Parent signal assignment:
1483: $SIG{INT} = $SIG{TERM} = \&HUNTSMAN;
1484:
1485: Child signal assignment:
1486: $SIG{INT} = 'DEFAULT'; (and SIGTERM is DEFAULT also)
1487: (The child dies and a SIGALRM is sent to parent, awaking parent from slumber
1488: to restart a new child.)
1489:
1490: Command-line invocations:
1491: B<kill> B<-s> SIGTERM I<PID>
1492: B<kill> B<-s> SIGINT I<PID>
1493:
1494: Subroutine B<HUNTSMAN>:
1495: This is only invoked for the B<lonc> parent I<PID>.
1496: This kills all the children, and then the parent.
1497: The B<lonc.pid> file is cleared.
1498:
1499: =item *
1500:
1501: SIGHUP
1502:
1503: Current bug:
1504: This signal can only be processed the first time
1505: on the parent process. Subsequent SIGHUP signals
1506: have no effect.
1507:
1508: Parent signal assignment:
1509: $SIG{HUP} = \&HUPSMAN;
1510:
1511: Child signal assignment:
1512: none (nothing happens)
1513:
1514: Command-line invocations:
1515: B<kill> B<-s> SIGHUP I<PID>
1516:
1517: Subroutine B<HUPSMAN>:
1518: This is only invoked for the B<lonc> parent I<PID>,
1519: This kills all the children, and then the parent.
1520: The B<lonc.pid> file is cleared.
1521:
1522: =item *
1523:
1524: SIGUSR1
1525:
1526: Parent signal assignment:
1527: $SIG{USR1} = \&USRMAN;
1528:
1529: Child signal assignment:
1530: $SIG{USR1}= \&logstatus;
1531:
1532: Command-line invocations:
1533: B<kill> B<-s> SIGUSR1 I<PID>
1534:
1535: Subroutine B<USRMAN>:
1536: When invoked for the B<lonc> parent I<PID>,
1537: SIGUSR1 is sent to all the children, and the status of
1538: each connection is logged.
1539:
1540:
1541: =back
1542:
1543: =cut
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