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Configuring communication between containers in QM and root partitions

Cross-environment communication works similar to communication within the QM partition. In addition to mounting a volume, or storage area, that contains a UNIX domain socket inside the quality-managed (QM) container, you must create another UNIX domain socket in the root partition to enable inter-process communication (IPC) between the containers in the two partitions.

Prerequisites

Procedure

  1. To configure IPC between the two containers, update the Quadlet configuration to mount the volumes that contain the UNIX domain sockets in /var/run/<another-dir>. In the example code, <another-dir> is my-ipc-demo, but you can name the directory according to your own conventions.

    1. To connect the engine application in the root partition with my-client-app in the QM partition, add this line to the engine.container file to mount the volume where the root socket resides in the container, and set the correct SELinux label:

      [Container]
Volume=/run/my-ipc-demo:/run/my-ipc-demo
SecurityLabelType=ipc_t

    2. Add this line to the my-client-app.container file to mount the volume where the root socket resides in the container:

      [Container]
Volume=/run/my-ipc-demo:/run/my-ipc-demo
SecurityLabelType=qm_container_ipc_t

  2. Create a Quadlet drop-in configuration for the QM container in the files/root_fs/qm.container.d/10-extra-volume.conf file:

    [Unit]
Requires=ipc.socket

[Container]
Volume=/run/my-ipc-demo:/run/my-ipc-demo

    Note

    QM configuration is built into the partition and should not be changed. Using drop-in files allows you to make additional modifications to the QM partition without overwriting the inherent configuration settings.

  3. Copy the drop-in Quadlet QM configuration file to the image:

    1. Add a new org.osbuild.mkdir stage in the rootfs pipeline of your manifest file:

      - type: org.osbuild.mkdir
  options:
    paths:
      - path: /etc/containers/systemd/qm.container.d
        exist_ok: true
        parents: true

    2. Add a new input item to the org.osbuild.copy stage in the rootfs pipeline of your manifest file:

      - type: org.osbuild.copy
  inputs:
    [...]
    inlinefile4:
      type: org.osbuild.files
      origin: org.osbuild.source
      mpp-embed:
        id: qm_extra_volume
        path: ../files/root_fs/qm.container.d/10-extra-volume.conf

  options:
    paths:
    [...]
    - from:
        mpp-format-string: input://inlinefile4/{embedded['qm_extra_volume']}
      to: tree:///etc/containers/systemd/qm.container.d/10-extra-volume.conf

  4. Optional: To use systemd to create a UNIX socket file, create a *.socket file with the same name as the service with which the socket is associated, such as engine.socket for the engine service.

    1. Create the systemd socket file in files/root_fs/engine.socket:

      [Unit]
Description=An example systemd unix socket

[Socket]
ListenStream=%t/my-ipc-demo/ipc.socket
RuntimeDirectory=my-ipc-demo

[Install]
WantedBy=sockets.target

      Note

      This step is optional because server application that binds and activates the UNIX socket can manage socket creation. However, systemd manages socket creation natively, which ultimately helps service synchronization.

    2. To enable the application to start after you create the socket, add these lines to the engine.container file to create a dependency with the systemd socket service:

      [Unit]
Requires=engine.socket
After=engine.socket

    3. To copy the systemd socket file for the QM container into the image, add a new input item to the org.osbuild.copy stage in the rootfs pipeline of your manifest file:

      - type: org.osbuild.copy
  inputs:
  [...]
    inlinefile5:
      type: org.osbuild.files
      origin: org.osbuild.source
      mpp-embed:
        id: engine_socket
        path: ../files/root_fs/engine.socket

  options:
    paths:
    [...]
    - from:
        mpp-format-string: input://inlinefile5/{embedded['engine_socket']}
      to: tree:///etc/systemd/system/engine.socket

  5. Optional: Set the SELinux configuration to permissive in the automotive image builder manifest:

    - type: org.osbuild.selinux.config
  options:
    state: permissive

Additional resources

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