Running Node.js as an Upstart service


Other posts in this series:

  1. Switching to Node.js
  2. Running Node.js as an Upstart service

I'm going to start with the final step first, being that it was the most vexing to solve, thanks to the vagaries of upstart configuration files. I know it seems backwards, but really, this was such a pain in the ass, it felt it demanded documentation as quickly as possible.

The node ecosystem, being a relatively young ecosystem, is missing some of the deployment tools that most other development enviroments have had for some time; this is most strikingly obvious when you're looking to deploy your node.js backend out on your live servers. My first question was "what's the equivilent of WSGI (or Rack or Servlets) for node?" (And yes I know that WSGI is blocking and Node is not, but the details of implementation aren't as important to this question as the existance of such a gateway.)

As far as I can find, the answer is none! You start your service using the command line and your script is responsible for creating a listener on a port. So long as you get traffic to the port on which it's listening — your service is going. You don't to worry about setting up an WSGI server, you don't have to handle any complex deployment scenarios — just get your code out on the server and run the command.

Obviously, then we need to consider the following:

  1. How to get node to run like a daemon
  2. How to start/stop the service along with all the other services
  3. How to restart the service automatically when it crashes
  4. How to handle running along side other web services on the same machine

Daemonizing your processes

*Sort of like press your luck...*

There are several ways to handle running a program as a non-interactive service. We could write it as a daemon process using fork/spawn and spawning the necessary processes for our script to daemonize itself or we could use a wrapper program like start-stop-daemon.*

Using child_process.spawn we could write our server specifically to spawn child processes. This, for some reason, feels messy — I'm trying to write a web-application, not a daemon, and would prefer to keep my code as clean as possible towards that singular purpose. I also don't really like writing daemons. I'd rather do:

import time, sys

try:
    respond_to_some_event_when_it_happens()
    while True:
        time.sleep(86400)
except KeyboardInterrupt:
    sys.exit(0)

Then be forced to handle daemonizing a process — I mean seriously, what has that cute little devil done to you! Ergo, I decided on start-stop-daemon which has a unix-appropriate-length man page for it, but more importantly, is designed to handle this exact scenario.

I figured the next two would be easy to tackle: since we're using Ubuntu linux on our AWS machines we will use Upstart, the system process management system that replaces the SYS V style init system with something a little more managed (similar to launchctl on NeXTMacOS).

Upstart has a vexing problem however: it's documentation, while volumnous for an open-source project kind of blows. The cookbook has no real recipies in it, and it's biggest problem: there's no way to validate the syntax of you upstart script. Either it runs or it doesn't. If it doesn't — good luck on figuring it out.

Some furious Googling later left me with the following upstart script:

# updater_node
#

description     "Updater node.js front end"
author          "Todd Kennedy"

start on runlevel [2345]

stop on runlevel [06]

respawn

# What environment are we in
env NODE_ENV=<%= node.chef_environment %>
env NODE_HOME=/var/opt/node

chdir $NODE_HOME/app

# Start the process
exec start-stop-daemon --start --chuid ubuntu --make-pidfile --pidfile $NODE_HOME/run/node-upstart.pid --exec /usr/local/bin/node -- $NODE_HOME/app/server.js >> $NODE_HOME/log/node-upstart.log 2>&1

(As you can see we are using chef to manage our deployments -- this just prints out the name of the appropriate environment: development, testing, production, so that our app can configure itself appropriately).

This gets placed into /etc/init/node.conf and can be run with the standard stop, start, restart, status, etc commands. But how do you know if you've gotten the syntax right? It will tab-complete when you try to interact with it: start no➥ should print out 'node'. If it doesn't you've, got some digging to do!

* I understand there are million and one ways to do this on unix, these are the two options I considered for this purpose however.

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About the Author

My name is Todd Kennedy, and I'm the Tech Lead at Condé Nast Traveler where I am responsible for our engineering team and the site. I've previously been employed at Updater, Spun (neé Broadcastr), NBCUniversal, Viacom and a slew of previous start-ups

The content on this blog does not reflect the views or positions of my employer, and should not be read to Mogwai after midnight.

I can be contacted via twitter or e-mail which is just my first name @ selfassemble.org.