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systemd

systemd is a commonly available init system (PID 1) on many Linux distributions. It offers process monitoring (including automatic restarts) and other useful features for running Puma in production.

Service Configuration

Below is a sample puma.service configuration file for systemd, which can be copied or symlinked to /etc/systemd/system/puma.service, or if desired, using an application or instance specific name.

Note that this uses the systemd preferred "simple" type where the start command remains running in the foreground (does not fork and exit). See also, the Alternative Forking Configuration below.

[Unit]
Description=Puma HTTP Server
After=network.target

# Uncomment for socket activation (see below)
# Requires=puma.socket

[Service]
# Foreground process (do not use --daemon in ExecStart or config.rb)
Type=simple

# Preferably configure a non-privileged user
# User=

# The path to the puma application root
# Also replace the "<WD>" place holders below with this path.
WorkingDirectory=

# Helpful for debugging socket activation, etc.
# Environment=PUMA_DEBUG=1

# The command to start Puma. This variant uses a binstub generated via
# `bundle binstubs puma --path ./sbin` in the WorkingDirectory
# (replace "<WD>" below)
ExecStart=<WD>/sbin/puma -b tcp://0.0.0.0:9292 -b ssl://0.0.0.0:9293?key=key.pem&cert=cert.pem

# Variant: Use config file with `bind` directives instead:
# ExecStart=<WD>/sbin/puma -C config.rb
# Variant: Use `bundle exec --keep-file-descriptors puma` instead of binstub

Restart=always

[Install]
WantedBy=multi-user.target

See systemd.exec for additional details.

Socket Activation

systemd and puma also support socket activation, where systemd opens the listening socket(s) in advance and provides them to the puma master process on startup. Among other advantages, this keeps listening sockets open across puma restarts and achieves graceful restarts, including when upgraded puma, and is compatible with both clustered mode and application preload. To use socket activation, configure one or more ListenStream sockets in a companion *.socket systemd config file. Here is a sample puma.socket, matching the ports used in the above puma.service:

[Unit]
Description=Puma HTTP Server Accept Sockets

[Socket]
ListenStream=0.0.0.0:9292
ListenStream=0.0.0.0:9293

# AF_UNIX domain socket
# SocketUser, SocketGroup, etc. may be needed for Unix domain sockets
# ListenStream=/run/puma.sock

# Socket options matching Puma defaults
NoDelay=true
ReusePort=true
Backlog=1024

[Install]
WantedBy=sockets.target

See systemd.socket for additional configuration details.

Note that the above configurations will work with Puma in either single process or cluster mode.

Usage

Without socket activation, use systemctl as root (e.g. via sudo) as with other system services:

# After installing or making changes to puma.service
systemctl daemon-reload

# Enable so it starts on boot
systemctl enable puma.service

# Initial start up.
systemctl start puma.service

# Check status
systemctl status puma.service

# A normal restart. Warning: listeners sockets will be closed
# while a new puma process initializes.
systemctl restart puma.service

With socket activation, several but not all of these commands should be run for both socket and service:

# After installing or making changes to either puma.socket or
# puma.service.
systemctl daemon-reload

# Enable both socket and service so they start on boot.  Alternatively
# you could leave puma.service disabled and systemd will start it on
# first use (with startup lag on first request)
systemctl enable puma.socket puma.service

# Initial start up. The Requires directive (see above) ensures the
# socket is started before the service.
systemctl start puma.socket puma.service

# Check status of both socket and service.
systemctl status puma.socket puma.service

# A "hot" restart, with systemd keeping puma.socket listening and
# providing to the new puma (master) instance.
systemctl restart puma.service

# A normal restart, needed to handle changes to
# puma.socket, such as changing the ListenStream ports. Note
# daemon-reload (above) should be run first.
systemctl restart puma.socket puma.service

Here is sample output from systemctl status with both service and socket running:

● puma.socket - Puma HTTP Server Accept Sockets
   Loaded: loaded (/etc/systemd/system/puma.socket; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2016-04-07 08:40:19 PDT; 1h 2min ago
   Listen: 0.0.0.0:9233 (Stream)
           0.0.0.0:9234 (Stream)

Apr 07 08:40:19 hx systemd[874]: Listening on Puma HTTP Server Accept Sockets.

● puma.service - Puma HTTP Server
   Loaded: loaded (/etc/systemd/system/puma.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2016-04-07 08:40:19 PDT; 1h 2min ago
 Main PID: 28320 (ruby)
   CGroup: /system.slice/puma.service
           ├─28320 puma 3.3.0 (tcp://0.0.0.0:9233,ssl://0.0.0.0:9234?key=key.pem&cert=cert.pem) [app]
           ├─28323 puma: cluster worker 0: 28320 [app]
           └─28327 puma: cluster worker 1: 28320 [app]

Apr 07 08:40:19 hx puma[28320]: Puma starting in cluster mode...
Apr 07 08:40:19 hx puma[28320]: * Version 3.3.0 (ruby 2.2.4-p230), codename: Jovial Platypus
Apr 07 08:40:19 hx puma[28320]: * Min threads: 0, max threads: 16
Apr 07 08:40:19 hx puma[28320]: * Environment: production
Apr 07 08:40:19 hx puma[28320]: * Process workers: 2
Apr 07 08:40:19 hx puma[28320]: * Phased restart available
Apr 07 08:40:19 hx puma[28320]: * Activated tcp://0.0.0.0:9233
Apr 07 08:40:19 hx puma[28320]: * Activated ssl://0.0.0.0:9234?key=key.pem&cert=cert.pem
Apr 07 08:40:19 hx puma[28320]: Use Ctrl-C to stop

Alternative Forking Configuration

Other systems/tools might expect or need puma to be run as a "traditional" forking server, for example so that the pumactl command can be used directly and outside of systemd for stop/start/restart. This use case is incompatible with systemd socket activation, so it should not be configured. Below is an alternative puma.service config sample, using Type=forking and the --daemon flag in ExecStart. Here systemd is playing a role more equivalent to SysV init.d, where it is responsible for starting Puma on boot (multi-user.target) and stopping it on shutdown, but is not performing continuous restarts. Therefore running Puma in cluster mode, where the master can restart workers, is highly recommended. See the systemd Restart directive for details.

[Unit]
Description=Puma HTTP Forking Server
After=network.target

[Service]
# Background process configuration (use with --daemon in ExecStart)
Type=forking

# Preferably configure a non-privileged user
# User=

# The command to start Puma
# Replace "<WD>" below, with the application root or working directory
ExecStart=bundle exec puma -C <WD>/shared/puma.rb --daemon

# The command to stop Puma
# Replace "<WD>" below
ExecStop=bundle exec pumactl -S <WD>/shared/tmp/pids/puma.state stop

# Path to PID file so that systemd knows which is the master process
PIDFile=<WD>/shared/tmp/pids/puma.pid

# Should systemd restart puma?
# Use "no" (the default) to ensure no interference when using
# stop/start/restart via `pumactl`.  The "on-failure" setting might
# work better for this purpose, but you must test it.
# Use "always" if only `systemctl` is used for start/stop/restart, and
# reconsider if you actually need the forking config.
Restart=no

[Install]
WantedBy=multi-user.target

capistrano3-puma

By default, capistrano3-puma uses pumactl for deployment restarts, outside of systemd. To learn the exact commands that this tool would use for ExecStart and ExecStop, use the following cap commands in dry-run mode, and update from the above forking service configuration accordingly. Note also that the configured User should likely be the same as the capistrano3-puma :puma_user option.

stage=production # or different stage, as needed
cap $stage puma:start --dry-run
cap $stage puma:stop  --dry-run