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Created July 9, 2021 07:12
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0-downtime deploy Unicorn Systemd
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0-downtime-deploy-Unicorn-Systemd
##Working configuration to accomplish 0-downtime deploy with unicorn 5.x and systemd on centos 7
The scope is to accomplish a 0-downtime reload of a [unicorn](https://unicorn.bogomips.org) service managed by Systemd on a Centos 7 distro.
The examples and assumptions that i found on the [bogomips's unicorn repo](http://unicorn.bogomips.org/examples/) seems not working for centos 7.
Below a working configuration tested on Centos 7 and unicorn 5.1
**Any advice/remark will be appreciated**
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unicorn.rb
# Sample verbose configuration file for Unicorn (not Rack)
#
# This configuration file documents many features of Unicorn
# that may not be needed for some applications. See
# http://unicorn.bogomips.org/examples/unicorn.conf.minimal.rb
# for a much simpler configuration file.
#
# See http://unicorn.bogomips.org/Unicorn/Configurator.html for complete
# documentation.
RAILS_ENV = 'production'
application_name = 'appname'
deploy_to = "/DOCROOT/#{application_name}"
# Use at least one worker per core if you're on a dedicated server,
# more will usually help for _short_ waits on databases/caches.
worker_processes 4
# Since Unicorn is never exposed to outside clients, it does not need to
# run on the standard HTTP port (80), there is no reason to start Unicorn
# as root unless it's from system init scripts.
# If running the master process as root and the workers as an unprivileged
# user, do this to switch euid/egid in the workers (also chowns logs):
user "appuser", "appgroup" #usually group has the same name of the user
# Help ensure your application will always spawn in the symlinked
# "current" directory that Capistrano sets up.
working_directory "#{deploy_to}/current" # available in 0.94.0+
# listen on both a Unix domain socket and a TCP port,
# we use a shorter backlog for quicker failover when busy
listen "#{deploy_to}/shared/tmp/sockets/unicorn.sock", :backlog => 64
# listen 8080, :tcp_nopush => true
# nuke workers after 30 seconds instead of 60 seconds (the default)
timeout 30
# feel free to point this anywhere accessible on the filesystem
pid "#{deploy_to}/shared/tmp/pids/unicorn.pid"
# By default, the Unicorn logger will write to stderr.
# Additionally, ome applications/frameworks log to stderr or stdout,
# so prevent them from going to /dev/null when daemonized here:
stderr_path "#{deploy_to}/shared/log/unicorn.stderr.log"
stdout_path "#{deploy_to}/shared/log/unicorn.stdout.log"
# combine Ruby 2.0.0dev or REE with "preload_app true" for memory savings
# http://rubyenterpriseedition.com/faq.html#adapt_apps_for_cow
#preload_app false #true
preload_app true
GC.respond_to?(:copy_on_write_friendly=) and
GC.copy_on_write_friendly = true
# Enable this flag to have unicorn test client connections by writing the
# beginning of the HTTP headers before calling the application. This
# prevents calling the application for connections that have disconnected
# while queued. This is only guaranteed to detect clients on the same
# host unicorn runs on, and unlikely to detect disconnects even on a
# fast LAN.
check_client_connection false
# local variable to guard against running a hook multiple times
run_once = true
before_fork do |server, worker|
# the following is highly recomended for Rails + "preload_app true"
# as there's no need for the master process to hold a connection
defined?(ActiveRecord::Base) and
ActiveRecord::Base.connection.disconnect!
# Occasionally, it may be necessary to run non-idempotent code in the
# master before forking. Keep in mind the above disconnect! example
# is idempotent and does not need a guard.
if run_once
# do_something_once_here ...
run_once = false # prevent from firing again
end
old_pid = "#{server.config[:pid]}.oldbin"
if File.exists?(old_pid) && server.pid != old_pid
begin
Process.kill("QUIT", File.read(old_pid).to_i)
rescue Errno::ENOENT, Errno::ESRCH
# someone else did our job for us
end
end
end
after_fork do |server, worker|
# per-process listener ports for debugging/admin/migrations
# addr = "127.0.0.1:#{9293 + worker.nr}"
# server.listen(addr, :tries => -1, :delay => 5, :tcp_nopush => true)
# the following is *required* for Rails + "preload_app true",
defined?(ActiveRecord::Base) and
ActiveRecord::Base.establish_connection
# if preload_app is true, then you may also want to check and
# restart any other shared sockets/descriptors such as Memcached,
# and Redis. TokyoCabinet file handles are safe to reuse
# between any number of forked children (assuming your kernel
# correctly implements pread()/pwrite() system calls)
end
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unicorn_app.service
#systemd unit file service for unicorn 5.x / Centos 7.x
[Unit]
Description=unicorn - app xxx
#After=nginx.service
[Service]
Type=forking
PIDFile=/DOCROOT/shared/tmp/pids/unicorn.pid
User=appuser
Group=appgroupname
WorkingDirectory=/DOCROOT/current
#Below, the rack env is set-up to none for production. It could be rewrited by rails init (you should export RAILS_ENV to the system)
ExecStart=/usr/local/rvm/wrappers/ruby-2.3.0/unicorn -c /DOCROOT/current/config/unicorn.rb -E none -D
ExecStop=/usr/bin/kill -QUIT $MAINPID
#USR2 signal will spawn the new master process, the kill signal to the old master should be send from rails
ExecReload=/bin/kill -s SIGUSR2 $MAINPID
CPUAccounting=true
MemoryAccounting=true
BlockIOAccounting=true
PrivateTmp=true
NoNewPrivileges=true
[Install]
WantedBy=multi-user.target
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