Elixir apps as systemd services - info & wiki

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I used mix in systemd to launch phx apps for a couple years. But it’s time to replace the simple service with a forked daemon. Here is where I’ll save my notes so when I have to do it again in 3 months and I google “elixir systemd service” I’ll find them again. Oh, and I guess if it helps someone else out, oh well. That’s the price I pay to be lazy.

Server: Ubuntu 20.04.5 LTS
Version: elixir 1.14.3 (compiled with Erlang/OTP 25) - with asdf
username: core (replace as you need)
project name: court (or court_api, replace as you need)

Build the release version in /opt/court_api

MIX_ENV=prod mix compile
MIX_ENV=prod mix assets.deploy
mix phx.gen.release
mix release

I like to load my entire environment from file rather than set each value in systemd’s config. These settings are all basic stuff except the PHX_SERVER=true is needed to tell the elixir daemon to launch the phoenix server. Also since I’m using asdf I include it’s shims and bin folder in the PATH.

vi /etc/environment-court

PATH="/home/core/.asdf/shims:/home/core/.asdf/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
SECRET_KEY_BASE=RlfalO4gogetyourownkeyzdNsLE
MIX_ENV=prod
DATABASE_URL=ecto://mydbuser:mypassword@192.168.1.257/court
PORT=5428
PHX_SERVER=true

Now setup the systemd service. Note I’m running it as daemon and not start. This forks it in the background or something like that. The takeaway is it is now running in the background. (If I was in Bash, I would get my prompt back)

vi /lib/systemd/system/court.service

[Unit]
Description=Court
After=network.target
Requires=network.target

[Service]
Type=forking
WorkingDirectory=/opt/court_api
User=core
Group=core
Restart=always
RestartSec=5
EnvironmentFile=/etc/environment-court
ExecStart=/opt/court_api/_build/prod/rel/court_api/bin/court_api daemon
ExecStop=/opt/court_api/_build/prod/rel/court_api/bin/court_api stop

[Install]
WantedBy=multi-user.target

Now restart systemd and start the new court service. I use restart because lets be honest, I’ll typo something or want to add RuntimeMaxSec.

systemctl daemon-reload
systemctl restart court

NOTES - Logs
Bad news is now that phx is running in the background, stdout isn’t caught by systemd. TODO: Look for or add a phx setting that will route stdout to syslog. Until that day, find your logs here:

tail -f /opt/court_api/_build/prod/rel/court_api/tmp/log/erlang.log.1

Not sure if elixir will rotate that or not. If not then something like this (not tested)

vi /etc/logrotate.d/elixir-court

/opt/court_api/_build/prod/rel/court_api/tmp/log/*log* {
  daily
  missingok
  rotate 14
  compress
  delaycompress
  notifempty
  create 640 core core
  sharedscripts  
}

NOTES - console
Losing journalctl logs sucks the big one, but this makes up for it! The ability to jump into the console and break things directly!

/opt/court_api/_build/prod/rel/court_api/bin/court_api remote

I hope I find these notes useful in 3 months when I have to do this again. (I hope someone replies back with the news that elixir/phx now detects if it has been launched in daemon mode and redirects stdout to syslogd)

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