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Automatically start containers
As of Docker 1.2, restart policies are the built-in Docker mechanism for restarting containers when they exit. If set, restart policies will be used when the Docker daemon starts up, as typically happens after a system boot. Restart policies will ensure that linked containers are started in the correct order.
If restart policies don't suit your needs (i.e., you have non-Docker processes that depend on Docker containers), you can use a process manager like upstart, systemd or supervisor instead.
Using a process manager
Docker does not set any restart policies by default, but be aware that they will conflict with most process managers. So don't set restart policies if you are using a process manager.
When you have finished setting up your image and are happy with your
running container, you can then attach a process manager to manage it.
When you run docker start -a, Docker will automatically attach to the
running container, or start it if needed and forward all signals so that
the process manager can detect when a container stops and correctly
restart it.
Here are a few sample scripts for systemd and upstart to integrate with Docker.
Examples
The examples below show configuration files for two popular process managers,
upstart and systemd. In these examples, we'll assume that we have already
created a container to run Redis with --name=redis_server. These files define
a new service that will be started after the docker daemon service has started.
upstart
description "Redis container"
author "Me"
start on filesystem and started docker
stop on runlevel [!2345]
respawn
script
/usr/bin/docker start -a redis_server
end script
systemd
[Unit]
Description=Redis container
Requires=docker.service
After=docker.service
[Service]
Restart=always
ExecStart=/usr/bin/docker start -a redis_server
ExecStop=/usr/bin/docker stop -t 2 redis_server
[Install]
WantedBy=default.target
If you intend to use this as a system service, put the above contents in a file
in the /etc/systemd/system directory, e.g.
/etc/systemd/system/docker-redis_server.service.
If you need to pass options to the redis container (such as --env),
then you'll need to use docker run rather than docker start. This will
create a new container every time the service is started, which will be stopped
and removed when the service is stopped.
[Service]
...
ExecStart=/usr/bin/docker run --env foo=bar --name redis_server redis
ExecStop=/usr/bin/docker stop -t 2 redis_server
ExecStopPost=/usr/bin/docker rm -f redis_server
...
To start using the service, reload systemd and start the service:
systemctl daemon-reload
systemctl start docker-redis_server.service
To enable the service at system startup, execute:
systemctl enable docker-redis_server.service