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Chapter 14. Porting containers to systemd using Podman

Podman (Pod Manager) is a fully featured container engine that is a simple daemonless tool. Podman provides a Docker-CLI comparable command line that makes the transition from other container engines easier and allows the management of pods, containers and images.

Podman was not originally designed to bring up an entire Linux system or manage services for such things as start-up order, dependency checking, and failed service recovery. That is the job of a full-blown initialization system like systemd. Red Hat has become a leader in integrating containers with systemd, so that OCI and Docker-formatted containers built by Podman can be managed in the same way that other services and features are managed in a Linux system. You can use the systemd initialization service to work with pods and containers. You can use the podman generate systemd command to generate a systemd unit file for containers and pods.

With systemd unit files, you can:

  • Set up a container or pod to start as a systemd service.
  • Define the order in which the containerized service runs and check for dependencies (for example making sure another service is running, a file is available or a resource is mounted).
  • Control the state of the systemd system using the systemctl command.

You can generate portable descriptions of containers and pods by using systemd unit files.

14.1. Enabling systemd services

When enabling the service, you have different options.

Procedure

  • Enable the service:

    • To enable a service at system start, no matter if user is logged in or not, enter: 

      # systemctl enable <service>

      You have to copy the systemd unit files to the /etc/systemd/system directory.

    • To start a service at user login and stop it at user logout, enter: 

      $ systemctl --user enable <service>

      You have to copy the systemd unit files to the $HOME/.config/systemd/user directory.

    • To enable users to start a service at system start and persist over logouts, enter:

      • In root mode: 

        # loginctl enable-linger <username>

      • In rootless mode: 

        $ loginctl enable-linger

Additional resources

14.2. Generating a systemd unit file using Podman

Podman allows systemd to control and manage container processes. You can generate a systemd unit file for the existing containers and pods using podman generate systemd command. It is recommended to use podman generate systemd because the generated units files change frequently (via updates to Podman) and the podman generate systemd ensures that you get the latest version of unit files.

Prerequisites

  • The container-tools module is installed.

Procedure

  1. Create a container (for example myubi): 

    $ podman create --name myubi registry.access.redhat.com/ubi8:latest sleep infinity
0280afe98bb75a5c5e713b28de4b7c5cb49f156f1cce4a208f13fee2f75cb453

  2. Use the container name or ID to generate the systemd unit file and direct it into the ~/.config/systemd/user/container-myubi.service file: 

    $ podman generate systemd --name myubi > ~/.config/systemd/user/container-myubi.service

Verification steps

  • Display the content of generated systemd unit file: 

    $ cat ~/.config/systemd/user/container-myubi.service
# container-myubi.service
# autogenerated by Podman 3.3.1
# Wed Sep  8 20:34:46 CEST 2021

[Unit]
Description=Podman container-myubi.service
Documentation=man:podman-generate-systemd(1)
Wants=network-online.target
After=network-online.target
RequiresMountsFor=/run/user/1000/containers

[Service]
Environment=PODMAN_SYSTEMD_UNIT=%n
Restart=on-failure
TimeoutStopSec=70
ExecStart=/usr/bin/podman start myubi
ExecStop=/usr/bin/podman stop -t 10 myubi
ExecStopPost=/usr/bin/podman stop -t 10 myubi
PIDFile=/run/user/1000/containers/overlay-containers/9683103f58a32192c84801f0be93446cb33c1ee7d9cdda225b78049d7c5deea4/userdata/conmon.pid
Type=forking

[Install]
WantedBy=multi-user.target default.target
    • The Restart=on-failure line sets the restart policy and instructs systemd to restart when the service cannot be started or stopped cleanly, or when the process exits non-zero.
    • The ExecStart line describes how we start the container.
    • The ExecStop line describes how we stop and remove the container.

Additional resources

14.3. Auto-generating a systemd unit file using Podman

By default, Podman generates a unit file for existing containers or pods. You can generate more portable systemd unit files using the podman generate systemd --new. The --new flag instructs Podman to generate unit files that create, start and remove containers.

Prerequisites

  • The container-tools module is installed.

Procedure

  1. Pull the image you want to use on your system. For example, to pull the httpd-24 image: 

    # podman pull registry.access.redhat.com/ubi8/httpd-24

  2. Optional. List all images available on your system: 

    # podman images
REPOSITORY                                TAG                  IMAGE ID      CREATED        SIZE
registry.access.redhat.com/ubi8/httpd-24  latest               8594be0a0b57  2 weeks ago    462 MB

  3. Create the httpd container: 

    # podman create --name httpd -p 8080:8080 registry.access.redhat.com/ubi8/httpd-24
cdb9f981cf143021b1679599d860026b13a77187f75e46cc0eac85293710a4b1

  4. Optional. Verify the container has been created: 

    # podman ps -a
CONTAINER ID  IMAGE                                            COMMAND               CREATED        STATUS      PORTS                   NAMES
cdb9f981cf14  registry.access.redhat.com/ubi8/httpd-24:latest  /usr/bin/run-http...  5 minutes ago  Created     0.0.0.0:8080->8080/tcp  httpd

  5. Generate a systemd unit file for the httpd container: 

    # podman generate systemd --new --files --name httpd
/root/container-httpd.service

  6. Display the content of the generated container-httpd.service systemd unit file: 

    # cat /root/container-httpd.service
# container-httpd.service
# autogenerated by Podman 3.3.1
# Wed Sep  8 20:41:44 CEST 2021

[Unit]
Description=Podman container-httpd.service
Documentation=man:podman-generate-systemd(1)
Wants=network-online.target
After=network-online.target
RequiresMountsFor=%t/containers

[Service]
Environment=PODMAN_SYSTEMD_UNIT=%n
Restart=on-failure
TimeoutStopSec=70
ExecStartPre=/bin/rm -f %t/%n.ctr-id
ExecStart=/usr/bin/podman run --cidfile=%t/%n.ctr-id --sdnotify=conmon --cgroups=no-conmon --rm -d --replace --name httpd -p 8080:8080 registry.access.redhat.com/ubi8/httpd-24
ExecStop=/usr/bin/podman stop --ignore --cidfile=%t/%n.ctr-id
ExecStopPost=/usr/bin/podman rm -f --ignore --cidfile=%t/%n.ctr-id
Type=notify
NotifyAccess=all

[Install]
WantedBy=multi-user.target default.target
Note

Unit files generated using the --new option do not expect containers and pods to exist. Therefore, they perform the podman run command when starting the service (see the ExecStart line) instead of the podman start command. For example, see section Generating a systemd unit file using Podman.

  • The podman run command uses the following command-line options:

    • The --conmon-pidfile option points to a path to store the process ID for the conmon process running on the host. The conmon process terminates with the same exit status as the container, which allows systemd to report the correct service status and restart the container if needed.
    • The --cidfile option points to the path that stores the container ID.
    • The %t is the path to the run time directory root, for example /run/user/$UserID.

    • The %n is the full name of the service.

      1. Copy unit files to /etc/systemd/system for installing them as a root user: 

        # cp -Z container-httpd.service /etc/systemd/system

      2. Enable and start the container-httpd.service: 

        # systemctl daemon-reload
# systemctl enable --now container-httpd.service
Created symlink /etc/systemd/system/multi-user.target.wants/container-httpd.service → /etc/systemd/system/container-httpd.service.
Created symlink /etc/systemd/system/default.target.wants/container-httpd.service → /etc/systemd/system/container-httpd.service.

Verification steps

  • Check the status of the container-httpd.service: 

    # systemctl status container-httpd.service
    ● container-httpd.service - Podman container-httpd.service
       Loaded: loaded (/etc/systemd/system/container-httpd.service; enabled; vendor preset: disabled)
       Active: active (running) since Tue 2021-08-24 09:53:40 EDT; 1min 5s ago
         Docs: man:podman-generate-systemd(1)
      Process: 493317 ExecStart=/usr/bin/podman run --conmon-pidfile /run/container-httpd.pid --cidfile /run/container-httpd.ctr-id --cgroups=no-conmon -d --repla>
      Process: 493315 ExecStartPre=/bin/rm -f /run/container-httpd.pid /run/container-httpd.ctr-id (code=exited, status=0/SUCCESS)
     Main PID: 493435 (conmon)
    ...

Additional resources

14.4. Auto-starting containers using systemd

You can control the state of the systemd system and service manager using the systemctl command. You can enable, start, stop the service as a non-root user. To install the service as a root user, omit the --user option.

Prerequisites

  • The container-tools module is installed.

Procedure

  1. Reload systemd manager configuration: 

    # systemctl --user daemon-reload

  2. Enable the service container.service and start it at boot time: 

    # systemctl --user enable container.service

  3. Start the service immediately: 

    # systemctl --user start container.service

  4. Check the status of the service: 

    $ systemctl --user status container.service
● container.service - Podman container.service
   Loaded: loaded (/home/user/.config/systemd/user/container.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2020-09-16 11:56:57 CEST; 8s ago
     Docs: man:podman-generate-systemd(1)
  Process: 80602 ExecStart=/usr/bin/podman run --conmon-pidfile //run/user/1000/container.service-pid --cidfile //run/user/1000/container.service-cid -d ubi8-minimal:>
  Process: 80601 ExecStartPre=/usr/bin/rm -f //run/user/1000/container.service-pid //run/user/1000/container.service-cid (code=exited, status=0/SUCCESS)
 Main PID: 80617 (conmon)
   CGroup: /user.slice/user-1000.slice/user@1000.service/container.service
           ├─ 2870 /usr/bin/podman
           ├─80612 /usr/bin/slirp4netns --disable-host-loopback --mtu 65520 --enable-sandbox --enable-seccomp -c -e 3 -r 4 --netns-type=path /run/user/1000/netns/cni->
           ├─80614 /usr/bin/fuse-overlayfs -o lowerdir=/home/user/.local/share/containers/storage/overlay/l/YJSPGXM2OCDZPLMLXJOW3NRF6Q:/home/user/.local/share/contain>
           ├─80617 /usr/bin/conmon --api-version 1 -c cbc75d6031508dfd3d78a74a03e4ace1732b51223e72a2ce4aa3bfe10a78e4fa -u cbc75d6031508dfd3d78a74a03e4ace1732b51223e72>
           └─cbc75d6031508dfd3d78a74a03e4ace1732b51223e72a2ce4aa3bfe10a78e4fa
             └─80626 /usr/bin/coreutils --coreutils-prog-shebang=sleep /usr/bin/sleep 1d

    You can check if the service is enabled using the systemctl is-enabled container.service command.

Verification steps

  • List containers that are running or have exited: 

    # podman ps
CONTAINER ID  IMAGE                            COMMAND  CREATED         STATUS             PORTS  NAMES
f20988d59920  registry.access.redhat.com/ubi8-minimal:latest  top      12 seconds ago  Up 11 seconds ago         funny_zhukovsky
Note

To stop container.service, enter: 

# systemctl --user stop container.service

Additional resources

14.5. Auto-starting pods using systemd

You can start multiple containers as systemd services. Note that the systemctl command should only be used on the pod and you should not start or stop containers individually via systemctl, as they are managed by the pod service along with the internal infra-container.

Prerequisites

  • The container-tools module is installed.

Procedure

  1. Create an empty pod, for example named systemd-pod: 

    $ podman pod create --name systemd-pod
11d4646ba41b1fffa51c108cbdf97cfab3213f7bd9b3e1ca52fe81b90fed5577

  2. Optional. List all pods: 

    $ podman pod ps
POD ID        NAME         STATUS   CREATED         # OF CONTAINERS  INFRA ID
11d4646ba41b  systemd-pod  Created  40 seconds ago  1                8a428b257111
11d4646ba41b1fffa51c108cbdf97cfab3213f7bd9b3e1ca52fe81b90fed5577

  3. Create two containers in the empty pod. For example, to create container0 and container1 in systemd-pod: 

    $ podman create --pod systemd-pod --name container0 registry.access.redhat.com/ubi8 top
$ podman create --pod systemd-pod --name container1 registry.access.redhat.com/ubi8 top

  4. Optional. List all pods and containers associated with them: 

    $ podman ps -a --pod
CONTAINER ID  IMAGE                                   COMMAND  CREATED        STATUS         PORTS   NAMES               POD ID        PODNAME
24666f47d9b2  registry.access.redhat.com/ubi8:latest  top      3 minutes ago  Created                container0          3130f724e229  systemd-pod
56eb1bf0cdfe  k8s.gcr.io/pause:3.2                             4 minutes ago  Created                3130f724e229-infra  3130f724e229  systemd-pod
62118d170e43  registry.access.redhat.com/ubi8:latest  top      3 seconds ago  Created                container1          3130f724e229  systemd-pod

  5. Generate the systemd unit file for the new pod: 

    $ podman generate systemd --files --name systemd-pod
/home/user1/pod-systemd-pod.service
/home/user1/container-container0.service
/home/user1/container-container1.service

    Note that three systemd unit files are generated, one for the systemd-pod pod and two for the containers container0 and container1.

  6. Display pod-systemd-pod.service unit file: 

    $ cat pod-systemd-pod.service
# pod-systemd-pod.service
# autogenerated by Podman 3.3.1
# Wed Sep  8 20:49:17 CEST 2021

[Unit]
Description=Podman pod-systemd-pod.service
Documentation=man:podman-generate-systemd(1)
Wants=network-online.target
After=network-online.target
RequiresMountsFor=
Requires=container-container0.service container-container1.service
Before=container-container0.service container-container1.service

[Service]
Environment=PODMAN_SYSTEMD_UNIT=%n
Restart=on-failure
TimeoutStopSec=70
ExecStart=/usr/bin/podman start bcb128965b8e-infra
ExecStop=/usr/bin/podman stop -t 10 bcb128965b8e-infra
ExecStopPost=/usr/bin/podman stop -t 10 bcb128965b8e-infra
PIDFile=/run/user/1000/containers/overlay-containers/1dfdcf20e35043939ea3f80f002c65c00d560e47223685dbc3230e26fe001b29/userdata/conmon.pid
Type=forking

[Install]
WantedBy=multi-user.target default.target
    • The Requires line in the [Unit] section defines dependencies on container-container0.service and container-container1.service unit files. Both unit files will be activated.
    • The ExecStart and ExecStop lines in the [Service] section start and stop the infra-container, respectively.

  7. Display container-container0.service unit file: 

    $ cat container-container0.service
# container-container0.service
# autogenerated by Podman 3.3.1
# Wed Sep  8 20:49:17 CEST 2021

[Unit]
Description=Podman container-container0.service
Documentation=man:podman-generate-systemd(1)
Wants=network-online.target
After=network-online.target
RequiresMountsFor=/run/user/1000/containers
BindsTo=pod-systemd-pod.service
After=pod-systemd-pod.service

[Service]
Environment=PODMAN_SYSTEMD_UNIT=%n
Restart=on-failure
TimeoutStopSec=70
ExecStart=/usr/bin/podman start container0
ExecStop=/usr/bin/podman stop -t 10 container0
ExecStopPost=/usr/bin/podman stop -t 10 container0
PIDFile=/run/user/1000/containers/overlay-containers/4bccd7c8616ae5909b05317df4066fa90a64a067375af5996fdef9152f6d51f5/userdata/conmon.pid
Type=forking

[Install]
WantedBy=multi-user.target default.target
    • The BindsTo line line in the [Unit] section defines the dependency on the pod-systemd-pod.service unit file
    • The ExecStart and ExecStop lines in the [Service] section start and stop the container0 respectively.

  8. Display container-container1.service unit file: 

    $ cat container-container1.service

  9. Copy all the generated files to $HOME/.config/systemd/user for installing as a non-root user: 

    $ cp pod-systemd-pod.service container-container0.service container-container1.service $HOME/.config/systemd/user

  10. Enable the service and start at user login: 

    $ systemctl enable --user pod-systemd-pod.service
Created symlink /home/user1/.config/systemd/user/multi-user.target.wants/pod-systemd-pod.service → /home/user1/.config/systemd/user/pod-systemd-pod.service.
Created symlink /home/user1/.config/systemd/user/default.target.wants/pod-systemd-pod.service → /home/user1/.config/systemd/user/pod-systemd-pod.service.

    Note that the service stops at user logout.

Verification steps

  • Check if the service is enabled: 

    $ systemctl is-enabled pod-systemd-pod.service
enabled

Additional resources

14.6. Auto-updating containers using Podman

The podman auto-update command allows you to automatically update containers according to their auto-update policy. The podman auto-update command updates services when the container image is updated on the registry. To use auto-updates, containers must be created with the --label "io.containers.autoupdate=image" label and run in a systemd unit generated by podman generate systemd --new command.

Podman searches for running containers with the "io.containers.autoupdate" label set to "image" and communicates to the container registry. If the image has changed, Podman restarts the corresponding systemd unit to stop the old container and create a new one with the new image. As a result, the container, its environment, and all dependencies, are restarted.

Prerequisites

  • The container-tools module is installed.

Procedure

  1. Start a myubi container based on the registry.access.redhat.com/ubi8/ubi-init image: 

    # podman run --label "io.containers.autoupdate=image" \
--name myubi -dt registry.access.redhat.com/ubi8/ubi-init top
bc219740a210455fa27deacc96d50a9e20516492f1417507c13ce1533dbdcd9d

  2. Optional: List containers that are running or have exited: 

    # podman ps -a
CONTAINER ID  IMAGE                                            COMMAND  CREATED         STATUS             PORTS   NAMES
76465a5e2933  registry.access.redhat.com/8/ubi-init:latest  top      24 seconds ago  Up 23 seconds ago          myubi

  3. Generate a systemd unit file for the myubi container: 

    # podman generate systemd --new --files --name myubi /root/container-myubi.service

  4. Copy unit files to /usr/lib/systemd/system for installing it as a root user: 

    # cp -Z ~/container-myubi.service /usr/lib/systemd/system

  5. Reload systemd manager configuration: 

    # systemctl daemon-reload

  6. Start and check the status of a container: 

    # systemctl start container-myubi.service
# systemctl status container-myubi.service

  7. Auto-update the container: 

    # podman auto-update

Additional resources

14.7. Auto-updating containers using systemd

As mentioned in section Auto-updating containers using Podman,

you can update the container using the podman auto-update command. It integrates into custom scripts and can be invoked when needed. Another way to auto update the containers is to use the pre-installed podman-auto-update.timer and podman-auto-update.service systemd service. The podman-auto-update.timer can be configured to trigger auto updates at a specific date or time. The podman-auto-update.service can further be started by the systemctl command or be used as a dependency by other systemd services. As a result, auto updates based on time and events can be triggered in various ways to meet individual needs and use cases.

Prerequisites

  • The container-tools module is installed.

Procedure

  1. Display the podman-auto-update.service unit file: 

    # cat /usr/lib/systemd/system/podman-auto-update.service

[Unit]
Description=Podman auto-update service
Documentation=man:podman-auto-update(1)
Wants=network.target
After=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/bin/podman auto-update

[Install]
WantedBy=multi-user.target default.target

  2. Display the podman-auto-update.timer unit file: 

    # cat /usr/lib/systemd/system/podman-auto-update.timer

[Unit]
Description=Podman auto-update timer

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target

    In this example, the podman auto-update command is launched daily at midnight.

  3. Enable the podman-auto-update.timer service at system start: 

    # systemctl enable podman-auto-update.timer

  4. Start the systemd service: 

    # systemctl start podman-auto-update.timer

  5. Optional: List all timers: 

    # systemctl list-timers --all
NEXT                         LEFT      LAST                         PASSED       UNIT                         ACTIVATES
Wed 2020-12-09 00:00:00 CET  9h left   n/a                          n/a          podman-auto-update.timer     podman-auto-update.service

    You can see that podman-auto-update.timer activates the podman-auto-update.service.

Additional resources