How can a runit' service restart return instantly?

Question

I have a runit service I use to run a rails app using unicorn .

Its restart command uses a signal (USR2) to handle a zero-downtime restart. Basically, it waits until the new process is ready before the old ones die.

This causes a very long (40 seconds) restart time, in which service myservice restart doesn't return until the end.

While I can give runit a longer timeout (which I already do), I want to make this restart a fire-and-forget kind of action so it'll return instantly (or after the USR2 signal was fired, but without waiting for it to complete.

The entire logic is taken from multiple blog posts about zero-downtime rails deployments with unicorn restarts:

• https://gist.github.com/czarneckid/4639793
• https://gist.github.com/JeanMertz/8996796
• https://nulogy.com/who-we-are/company-blog/articles/zero-downtime-deployments-with-chef-nginx-and-unicorn/

This is the runit script (generated by chef):

#!/bin/bash
#
# This file is managed by Chef, using the <%= node.name %> cookbook.
# Editing this file by hand is highly discouraged!
#

exec 2>&1

#
# Since unicorn creates a new pid on restart/reload, it needs a little extra
# love to manage with runit. Instead of managing unicorn directly, we simply
# trap signal calls to the service and redirect them to unicorn directly.
#


RUNIT_PID=$$
APPLICATION_NAME=<%= @options[:application_name] %>
APPLICATION_PATH=<%= File.join(@options[:path], 'current') %>
BUNDLE_CMD="<%= @options[:bundle_command] ? "#{@options[:bundle_command]} exec" : '' %>"
UNICORN_CMD=<%= @options[:unicorn_command] ? @options[:unicorn_command] : 'unicorn' %>
UNICORN_CONF=<%= @options[:unicorn_config_path] ? @options[:unicorn_config_path] : File.join(@options[:path], 'current', 'config', 'unicorn.rb') %>
RAILS_ENV=<%= @options[:rails_env] %>
CUR_PID_FILE=<%= @options['pid'] ? @options['pid'] : File.join(@options[:path], 'current', 'shared', 'pids', "#{@options[:application_name]}.pid") %>
ENV_PATH=<%= @options[:env_dir] %>
OLD_PID_FILE=$CUR_PID_FILE.oldbin

echo "Runit service restarted (PID: $RUNIT_PID)"

function is_unicorn_alive {
  set +e
  if [ -n $1 ] && kill -0 $1 >/dev/null 2>&1; then
    echo "yes"
  fi
  set -e
}

if [ -e $OLD_PID_FILE ]; then
  OLD_PID=$(cat $OLD_PID_FILE)
  echo "Old master detected (PID: $OLD_PID), waiting for it to quit"
  while [ -n "$(is_unicorn_alive $OLD_PID)" ]; do
    sleep 5
  done
fi

if [ -e $CUR_PID_FILE ]; then
  CUR_PID=$(cat $CUR_PID_FILE)
  if [ -n "$(is_unicorn_alive $CUR_PID)" ]; then
    echo "Detected running Unicorn instance (PID: $CUR_PID)"
    RUNNING=true
  fi
fi

function start {
  unset ACTION
  if [ $RUNNING ]; then
    restart
  else
    echo 'Starting new unicorn instance'
    cd $APPLICATION_PATH

    exec chpst -e $ENV_PATH $BUNDLE_CMD $UNICORN_CMD -c $UNICORN_CONF -E $RAILS_ENV
    sleep 3
    CUR_PID=$(cat $CUR_PID_FILE)
  fi
}

function stop {
  unset ACTION
  echo 'Initializing graceful shutdown'
  kill -QUIT $CUR_PID

  while [ -n "$(is_unicorn_alive $CUR_PID)" ]; do
    echo '.'
    sleep 2
  done

  echo 'Unicorn stopped, exiting Runit process'
  kill -9 $RUNIT_PID
}

function restart {
  unset ACTION
  echo "Restart request captured, swapping old master (PID: $CUR_PID) for new master with USR2"
  kill -USR2 $CUR_PID

  sleep 2
  echo 'Restarting Runit service to capture new master PID'
  exit
}

function alarm {
  unset ACTION
  echo 'Unicorn process interrupted'
}

trap 'ACTION=stop' STOP TERM KILL
trap 'ACTION=restart' QUIT USR2 INT
trap 'ACTION=alarm' ALRM

[ $RUNNING ] || ACTION=start

if [ $ACTION ]; then
  echo "Performing \"$ACTION\" action and going into sleep mode until new signal captured"
elif [ $RUNNING ]; then
  echo "Going into sleep mode until new signal captured"
fi

if [ $ACTION ] || [ $RUNNING ]; then
  while true; do
    [ "$ACTION" == 'start' ] && start
    [ "$ACTION" == 'stop' ] && stop
    [ "$ACTION" == 'restart' ] && restart
    [ "$ACTION" == 'alarm' ] && alarm
    sleep 2
  done
fi

Answer 1

This is a super weird way to use Runit, move your reload logic to the control/h script and use sv hup (or since it doesn't seem to be anything more than sending USR2 sv 2 ). The main run script shouldn't be involved.