Hi Eric,
On Mon, Nov 30, 2009 at 3:47 PM, Suraj Kurapati wrote:
> from Capistrano, I send SIGUSR2 to the existing Unicorn master (which
> will become the old Unicorn master), wait 90 seconds, and then send
> SIGQUIT to the old Unicorn master. [...] The only thing I'm worried
> about is that I'll have to keep adjusting this timeout as the
> infrastructure my app depends upon becomes slower/faster. A
> when_ready() hook would really do wonders for me
Inspired by your solution[1] to a recent question about forking, I
solved this problem by temporarily sneaking into the build_app! method
and killing the old Unicorn master after the Rails app has been built:
before_fork do |server, worker|
#
# the following allows a new master process to incrementally
# phase out the old master process with SIGTTOU to avoid a
# thundering herd (especially in the "preload_app false" case)
# when doing a transparent upgrade. The last worker spawned
# will then kill off the old master process with a SIGQUIT.
#
old_pid_file = server.config[:pid].to_s + '.oldbin'
if File.exist? old_pid_file and
server.pid != old_pid_file and
worker.nr == server.worker_processes-1
then
#
# wait until Rails app is built and ready to serve (we do this by
# sneaking into Unicorn's build_app! method) by the last worker
# process inside the new Unicorn before stopping old Unicorn
#
orig_meth_name = :build_app!
orig_meth_impl = server.method(orig_meth_name)
server_metaclass = class << server; self; end
server_metaclass.class_eval do
# replace Unicorn's method with our own sneaky version
define_method orig_meth_name do
# behave like Unicorn's original method
orig_meth_impl.call
# do our sneaky business! (kill the old Unicorn)
begin
Process.kill :QUIT, File.read(old_pid_file).to_i
rescue Errno::ENOENT, Errno::ESRCH
# ignore
end
# restore Unicorn's original method
server_metaclass.class_eval do
define_method orig_meth_name, orig_meth_impl
end
end
end
end
end
Thanks for your help! :)
[1]: http://article.gmane.org/gmane.comp.lang.ruby.unicorn.general/425
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