Red Hat OpenShift Development I: Introduction to Containers with Podman

Instructions

1. Create a container that runs an Apache HTTP server in the background.

   1. Execute the podman run command to create the container. Expose the 8080 port and use the registry.ocp4.example.com:8443/ubi8/httpd-24 image.

      [student@workstation ~]$ podman run --name httpd -d -p \
       8080:8080 registry.ocp4.example.com:8443/ubi8/httpd-24
      Trying to pull registry.ocp4.example.com:8443/ubi8/httpd-24:latest...
      ...output omitted...

2. Verify that the container is running.

   1. Use podman ps to list all the running containers.

      [student@workstation ~]$ podman ps
      CONTAINER ID    IMAGE        COMMAND         CREATED STATUS PORTS       NAMES
      ID              registry...  ...run-http...  ...ago  Up...  ...8080/tcp httpd

   2. Use the podman inspect command to get the Status field, which indicates whether the container is running.

      [student@workstation ~]$ podman inspect --format='{{.State.Status}}' httpd
      running

   3. Verify that the container is running by using the Running field.

      [student@workstation ~]$ podman inspect --format='{{.State.Running}}' httpd
      true

   4. In a web browser, navigate to localhost:8080 to verify that the Apache server is running.

3. Stop the container.

   1. Return to your command-line terminal. Use the container name to stop the container.

      [student@workstation ~]$ podman stop httpd
      httpd

   2. Retrieve the Status of the container.

      [student@workstation ~]$ podman inspect --format='{{.State.Status}}' httpd
      exited

   3. Verify that the container is not running.

      [student@workstation ~]$ podman inspect --format='{{.State.Running}}' httpd
      false

   4. In a web browser, verify that the Apache server is no longer accessible at the 8080 port.

4. Restart the container.

   1. In your command-line terminal, use the podman restart command to restart the container.

      [student@workstation ~]$ podman restart httpd
      CONTAINER_ID

   2. Verify that the container is running again.

      [student@workstation ~]$ podman ps
      CONTAINER ID    IMAGE        COMMAND         CREATED STATUS PORTS       NAMES
      ID              registry...  ...run-http...  ...ago  Up...  ...8080/tcp httpd

   3. In a web browser, verify that the Apache server is running by navigating to http://localhost:8080.

5. Remove the container.

   1. Try to remove the running container by using the podman rm command.

      [student@workstation ~]$ podman rm httpd
      Error: cannot remove container CONTAINER_ID as it is running - running or paused containers cannot be removed without force: container state improper

      Podman requires that you to stop the container before you can remove it. However, you can force the removal of the container by adding the --force flag.

   2. Force the removal of the container.

      [student@workstation ~]$ podman rm httpd --force
      78f3...bc672

6. Verify that the container has been removed.

   1. Try to retrieve the status of the container.

      [student@workstation ~]$ podman inspect --format='{{.State.Running}}' httpd
      Error: error inspecting object: no such object: "httpd"

      Because you removed the container, you can no longer retrieve its status.

7. Forcefully stop a container that does not respond to the SIGTERM signal.

   1. Start a new container in the background by using the registry.ocp4.example.com:8443/redhattraining/podman-greeter-ignore-sigterm image. The application ignores SIGTERM signals.

      [student@workstation ~]$ podman run --name greeter -d \
      registry.ocp4.example.com:8443/redhattraining/podman-greeter-ignore-sigterm
      ...output omitted...
      f919...e69b

   2. Try to stop the container with a grace period of 5 seconds.

      [student@workstation ~]$ podman stop greeter --time=5
      WARN[0005] StopSignal SIGTERM failed to stop container greeter in 5 seconds, resorting to SIGKILL
      greeter

      Podman sends a SIGTERM signal to stop the container gracefully, but the application ignores the signal. After 5 seconds, Podman sends a SIGKILL signal to the container. The --time flag indicates the time that Podman waits before sending a SIGKILL signal to forcefully stop the container.

   3. Restart the container.

      [student@workstation ~]$ podman restart greeter
      f919...e69b

   4. Use the podman kill command to directly send a SIGKILL signal and stop the container forcefully.

      [student@workstation ~]$ podman kill greeter
      greeter