> For the complete documentation index, see [llms.txt](https://ondrej-kvasnovsky-2.gitbook.io/docker-handbook/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ondrej-kvasnovsky-2.gitbook.io/docker-handbook/picking-os/systemd.md). # Running Services We are not going to explain all about `systemd`, just what we are going to use to run our services as docker containers. ## Why systemd? * concise "unit files" * process dependencies * unified toolset ## How to use systemd? ### Unit files List unit files created by Debian. ``` sudo systemctl list-unit-files ``` Unit files have multiple sections. Unit section have description and dependencies, like dependency to network.target that needs to be executed first. Service sections have type `oneshot` and it makes sure that action will be executed. Install sections says another dependency, when this should be started. ``` [Unit] Description=Restore iptables firewall rules Before=network.target Conflicts=shutdown.target [Service] Type=oneshot ExecStart=/sbin/iptables-restore /var/lib/iptables/rules-save [Install] WantedBy=basic.target ``` ### Postgres service Service sections can have multiple phases. `%p` will resolve to name of the service, which is name of the file, `postgres.service`. It says the service needs to be started after docker service is up. Also, it says the service needs to be always restarted, which will make the service running all the time. ``` [Unit] Description=Run %p Requires=docker.service After=docker.service [Service] Restart=always ExecStartPre=-/usr/bin/docker kill %p ExecStartPre=-/usr/bin/docker rm -f %p ExecStart=/usr/bin/docker run --rm --name %p \ -v /var/lib/postgresql/data:/var/lib/postgresql/data \ -p 5432:5432 %p:9.4.5 ExecStop=/usr/bin/docker stop %p [Install] WantedBy=multi-user.target ``` ### Mobydock service (the example service) Here is the file that will make sure our example service is running. ``` [Unit] Description=Run %p Requires=docker.service postgres.service redis.service After=docker.service postgres.service redis.service [Service] Restart=always User=ondrej ExecStartPre=-/usr/bin/docker kill %p ExecStartPre=-/usr/bin/docker rm -f %p ExecStart=/usr/bin/docker run -t --rm --name %p \ --link redis:redis --link postgres:postgres \ -v /home/ondrej/instance:/mobydock/instance \ -p 8000:8000 %p ExecStartPost=-/usr/bin/docker stop nginx ExecStop=/usr/bin/docker stop %p [Install] WantedBy=multi-user.target nginx.service ``` ### Redis service Here is the Redis service, `redis.service`. ``` [Unit] Description=Run %p Requires=docker.service After=docker.service [Service] Restart=always ExecStartPre=-/usr/bin/docker kill %p ExecStartPre=-/usr/bin/docker rm -f %p ExecStart=/usr/bin/docker run --rm --name %p \ -v /var/lib/%p/data:/var/lib/%p/data -p 6379:6379 %p:2.8.22 ExecStop=/usr/bin/docker stop %p [Install] WantedBy=multi-user.target ``` ## Put unit files on staging server Lets see how we can put postgres.service on server and apply that. First connect to the server and create the file. Then change owner. ``` $ ssh ondrej@192.168.1.199 $ sudo vi /etc/systemd/system/postgres.service $ sudo chown ondrej:ondrej /etc/systemd/system/postgres.service $ sudo vi /etc/systemd/system/redis.service $ sudo chown ondrej:ondrej /etc/systemd/system/redis.service $ sudo vi /etc/systemd/system/mobydock.service $ sudo chown ondrej:ondrej /etc/systemd/system/mobydock.service ``` Now, lets enable the services. Enable will make sure it is loaded at the system boot. Start will start it immediately. ``` $ sudo systemctl enable postgres.service $ sudo systemctl start postgres.service $ sudo systemctl enable redis.service $ sudo systemctl start redis.service $ sudo systemctl enable mobydock.service $ sudo systemctl start mobydock.service ``` Now we can try to play with the services. Lets try to restart redis service and see, that redis the docker container was just started. ``` $ sudo systemctl restart redis.service $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 95e593bbb735 redis:2.8.22 "/entrypoint.sh redi…" 1 second ago Up 1 second 0.0.0.0:6379->6379/tcp redis 0d859124baf9 postgres:9.4.5 "/docker-entrypoint.…" 6 minutes ago Up 6 minutes 0.0.0.0:5432->5432/tcp postgres ``` ## Disable a service We can disable the service. ``` $ sudo systemctl disable redis.service ``` ## Service status We can find out the status of the service. This is useful when debugging the service. ``` $ sudo systemctl status redis.service ● redis.service - Run redis Loaded: loaded (/etc/systemd/system/redis.service; enabled; vendor preset: enabled) Active: active (running) since Thu 2018-01-04 22:29:36 PST; 4min 27s ago Process: 1513 ExecStop=/usr/bin/docker stop redis (code=exited, status=0/SUCCESS) Process: 1570 ExecStartPre=/usr/bin/docker rm -f redis (code=exited, status=1/FAILURE) Process: 1565 ExecStartPre=/usr/bin/docker kill redis (code=exited, status=1/FAILURE) Main PID: 1575 (docker) Tasks: 8 (limit: 4915) Memory: 4.6M CPU: 26ms CGroup: /system.slice/redis.service └─1575 /usr/bin/docker run --rm --name redis -v /var/lib/redis/data:/var/lib/redis/data -p 6379:6379 redis:2.8.22 Jan 04 22:29:36 stagingserver docker[1575]: |`-._`-._ `-.__.-' _.-'_.-'| Jan 04 22:29:36 stagingserver docker[1575]: | `-._`-._ _.-'_.-' | Jan 04 22:29:36 stagingserver docker[1575]: `-._ `-._`-.__.-'_.-' _.-' Jan 04 22:29:36 stagingserver docker[1575]: `-._ `-.__.-' _.-' Jan 04 22:29:36 stagingserver docker[1575]: `-._ _.-' Jan 04 22:29:36 stagingserver docker[1575]: `-.__.-' Jan 04 22:29:36 stagingserver docker[1575]: [1] 05 Jan 06:29:36.877 # Server started, Redis version 2.8.22 Jan 04 22:29:36 stagingserver docker[1575]: [1] 05 Jan 06:29:36.877 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. Jan 04 22:29:36 stagingserver docker[1575]: [1] 05 Jan 06:29:36.877 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somax Jan 04 22:29:36 stagingserver docker[1575]: [1] 05 Jan 06:29:36.877 * The server is now ready to accept connections on port 6379 ... ``` ## Reloading services When we update the service file, we want to reload the changes. ``` $ sudo systemctl daemon-reload ``` ## Service crash What happens when the service crashes? Lets try it out. Lets kill Redis service. We can see that when we kill the service, is is started again, thanks to `systemd`. ``` $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 95e593bbb735 redis:2.8.22 "/entrypoint.sh redi…" 8 minutes ago Up 8 minutes 0.0.0.0:6379->6379/tcp redis 0d859124baf9 postgres:9.4.5 "/docker-entrypoint.…" 14 minutes ago Up 14 minutes 0.0.0.0:5432->5432/tcp postgres $ docker stop 95e593bbb735 95e593bbb735 $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 0629c8d39127 redis:2.8.22 "/entrypoint.sh redi…" 2 seconds ago Up Less than a second 0.0.0.0:6379->6379/tcp redis 0d859124baf9 postgres:9.4.5 "/docker-entrypoint.…" 14 minutes ago Up 14 minutes 0.0.0.0:5432->5432/tcp postgres ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. 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