Server Starter - a superdaemon to hot-deploy server programs
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Server::Starter is a superdaemon that allows for hot deployment of server programs without downtime or resource leaks. It works by binding to TCP ports and spawning application server processes to handle connections while signaling old processes to shutdown when new ones are launched. This allows servers to be upgraded without interrupting service and prevents issues like file descriptor leaks that can occur with other hot deployment techniques. The superdaemon approach ensures new processes launch successfully before retiring old ones, providing a fail-safe deployment mechanism.
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Server Starter - a superdaemon to hot-deploy server programs
- 1. Server::Starter a superdaemon to hot-deploy server programs Cybozu Labs, Inc. Kazuho Oku
- 2. Hot deployment what is it? upgrading web application without restarting the application server the goals no downtime no resource leaks fail-safe Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 2
- 3. Current techniques restart the interpreter (mod_perl) pros: graceful cons: XS may cause resource leaks, service-down on deployment failure, cannot implement in pure- perl bind to unix socket (FastCGI) pros: graceful, fail-safe cons: only useful for local-machine communication Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 3
- 4. Current techniques (cont'd) exec(myself) (Net::Server) pros: graceful, pure-perl cons: file descriptor leaks, service-down on deployment failure Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 4
- 5. Server::Starter a superdaemon for hot-deploying TCP servers superdaemon binds to TCP ports, then spawns the application server listen accept fork & exec SIGTERM app. logic accept spawn app. servers fork & exec app. logic SIGHUP Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 5
- 6. Reaching the Goals Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 6
- 7. No downtime listening socket shared by old and new generation app. servers old app. servers receive SIGTERM after new servers start listen accept fork & exec SIGTERM accept logic app. spawn app. servers fork & exec app. logic SIGHUP Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 7
- 8. No resource leaks no chance of resource leaks every generation of app. servers spawned from superdaemon listen accept fork & exec SIGTERM accept logic app. spawn app. servers fork & exec app. logic SIGHUP Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 8
- 9. Fail-safe old app. server retired if and only if the new app. server starts up successfully service continues even if the updated app. server fails to start, in cases like missing modules, etc. a good practice is to do self-testing in the app. server before starting to serve client connections is also an efficient way to preload modules listen accept fork & exec SIGTERM accept logic app. spawn app. servers fork & exec app. logic SIGHUP Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 9
- 10. Demo Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 10
- 11. Using Server::Starter Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 11
- 12. The Low-level Code # from command line % start_server --port=80 my_httpd # in my_httpd use Server::Starter qw(server_ports); my $listen_sock = IO::Socket::INET->new( Proto => 'tcp', ); $listen_sock->fdopen((values %{server_ports()})[0], 'w') or die "failed to bind to listening socket:$!"; while (1) { if (my $conn = $listen_sock->accept) { .... } } Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 12
- 13. Net::Server::SS::PreFork subclass of Net::Server::PreFork # from command line % start_server --port=80 my_server.pl # in my_server.pl use base qw(Net::Server::SS::PreFork); sub process_request { #...code... } __PACKAGE__->run(); Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 13
- 14. Using together with HTTP::Server::Simple HTTP::Server::Simple can use Net::Server::SS::PreFork as a backend and many WAFs support HTTP::Server::Simple package MyServer; use base qw(HTTP::Server::Simple::CGI); sub net_server { 'Net::Server::SS::PreFork' }; sub handle_request { print "HTTP/1.0 200 HOKrnContent-Type: text/plainrnrnHello World"; } 1; Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 14
- 15. Using together with PSGI / Plack started writing Plack::Impl::SSPreFork on my github fork of Plack uid, etc. aren't configurable yet :-( # from command line % start_server --port=80 -- plackup -i SSPreFork MyApp.pm Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 15
- 16. Launching from daemontools daemontools a (better) alternative to init.d scripts, by DJB start_server script is designed to be run under daemontools restart using –h (SIGHUP) all logs to STDERR Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 16
- 17. ToDo Support for FastCGI although ... (ry init.d-style startup mode Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 17
- 18. Conclusion with Server::Starter, it is easy to write hot-deployable TCP servers Sep 10 2009 Server::Starter - a superdaemon to hot-deploy server programs 18