Decouple the sending of client restart events from the restarting of
the servers. Restarts use the new Tornado restart-clients endpoint to
inject "restart" events into queues of clients which were loaded from
the previous Tornado process. The rate is controlled by the
`application_server.client_restart_rate`, in clients per minute, or a
flag to `restart-clients` which overrides it. Note that a web client
will also spread its restart over 5 minutes, so artificially-slow
client restarts are generally not very necessary.
Restarts of clients are deferred to until after post-deploy hooks are
run, such that the pre- and post- deploy hooks are around the actual
server restarts, even if pushing restart events to clients takes
significant time.
Alex Vandiver