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).

[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 your application code root directory.
# Also replace the "<YOUR_APP_PATH>" place holders below with this path.
# Example /home/username/myapp
WorkingDirectory=<YOUR_APP_PATH>

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

# SystemD will not run puma even if it is in your path. You must specify
# an absolute URL to puma. For example /usr/local/bin/puma
# Alternatively, create a binstub with `bundle binstubs puma --path ./sbin` in the WorkingDirectory
ExecStart=/<FULLPATH>/bin/puma -C <YOUR_APP_PATH>/puma.rb

# Variant: Rails start.
# ExecStart=/<FULLPATH>/bin/puma -C <YOUR_APP_PATH>/config/puma.rb ../config.ru

# Variant: Use `bundle exec --keep-file-descriptors puma` instead of binstub
# Variant: Specify directives inline.
# ExecStart=/<FULLPATH>/puma -b tcp://0.0.0.0:9292 -b ssl://0.0.0.0:9293?key=key.pem&cert=cert.pem


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.

Note: Any wrapper scripts which exec, or other indirections in ExecStart, may result in activated socket file descriptors being closed before they reach the puma master process. For example, if using bundle exec, pass the --keep-file-descriptors flag. bundle exec can be avoided by using a puma executable generated by bundle binstubs puma. This is tracked in [#1499].

Note: Socket activation doesn't currently work on JRuby. This is tracked in #1367.

To use socket activation, configure one or more ListenStream sockets in a companion *.socket unit file. Also uncomment the associated Requires directive for the socket unit in the service file (see above.) 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.

Sockets and symlinks

When using releases folders, you should set the socket path using the shared folder path (ex. /srv/projet/shared/tmp/puma.sock), not the release folder path (/srv/projet/releases/1234/tmp/puma.sock).

Puma will detect the release path socket as different than the one provided by systemd and attempt to bind it again, resulting in the exception There is already a server bound to:.

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

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

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