Chapter 2. Managing Containers

To Prepare a Container Host:

1. Prepare a Red Hat Enterprise Linux 7 server for hosting images and enable the docker service on this server as described in the Getting Docker in RHEL 7 section of the Get Started with Docker Formatted Container Images on Red Hat Systems guide on the Red Hat Customer Portal. You can deploy the container host either on the same machine as the Satellite Server or independently.

   Note

   Red Hat Enterprise Linux 7 is currently the only supported system for a container host. The docker package is available in the rhel-7-server-extras-rpms repository. Red Hat Enterprise Linux 6 systems are currently not supported to host containers.

2. Run the following command on the container host to install the Satellite Server’s CA certificate:

   rpm -Uvh https://satellite.example.com/pub/katello-ca-consumer-latest.noarch.rpm

   Here, satellite.example.com is the fully qualified domain name of your Satellite Server. Skip this step if the container host is already registered as a Satellite host.

3. Depending on the location of the container host, perform the following tasks:

   1. If the container host is on the same machine as the Satellite Server:

      1. Create a docker user group and add the foreman user to it:

         # groupadd docker
         # usermod -aG docker foreman

      2. Modify the OPTIONS variable in the /etc/sysconfig/docker file as follows:

         OPTIONS='--selinux-enabled -G docker'

      3. Restart the affected services to apply the changes:

         # systemctl restart docker.service
         # katello-service restart

   2. If the container host is on a different machine than the Satellite Server:

      1. Open a port on the container host to communicate with the Satellite Server. To do so, modify the OPTIONS variable in the /etc/sysconfig/docker file as follows:

         OPTIONS='--selinux-enabled -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock'

         You can use port 2376 if TLS is enabled.

      2. Restart the docker service and verify your settings as follows:

         # systemctl restart docker.service
         # systemctl status docker.service

To Create a Docker Compute Resource:

1. Make sure the port 5000 is enabled on the Satellite Server. The container host uses this port to pull images from Content Views on the Satellite Server.

2. Create the compute resource as described in Adding an Atomic Host Connection to the Satellite Server in the Provisioning Guide. Specify the resource URL according to the location of the container host:

   1. If the container host is on the same machine as the Satellite Server, set unix://var/run/docker.sock as the resource URL.

3. If the container host is on a different machine than the Satellite Server, specify the URL in the form of:

   http://container_host_fqdn:2375

   Here, container_host_fqdn stands for the fully qualified domain name of the container host, and the port number opened on the container host for communication with Satellite can be either 2375 or, if using TLS, 2376.

4. Click Test Connection to test if the container host is available.
5. Click Submit to create the compute resource.

To Create a Container:

1. Navigate to Containers > New Container. Alternatively, navigate to Containers > All Containers and click New container.

2. In the Preliminary stage of container creation, configure the following settings:

   • On the Compute resource tab, select the compute resource from the Deployed on drop-down menu. For more information on compute resources, see Defining the Provisioning Workflow in the Provisioning Guide.
   • On the Locations tab, select the locations where the new container will be available.

   • On the Organizations tab, select the organizations where the new container will be available.

     Click Next to proceed.

3. In the Image stage of container creation, import an image that will act as a base for your container. This can be a platform image, or a previously created layered image. Select from one of the following options:

   • Select the Content View tab to import the image from a life cycle environment. Specify the life cycle environment, Content View, repository, tag, and Capsule Server.
   • Select the Docker hub tab to import the image from the Docker Hub registry. After you type the image name to the Search field, Satellite automatically searches the compute resource. Click the looking glass icon to search the Docker Hub. Select the image from the list of search results and pick a tag from the drop-down list.

   • Select the External registry tab to import the image from an existing registry. Select the registry from the drop-down menu, and search it by the image name. Satellite populates the Tag field with tags available for the selected image name. For more information, see Importing Container Images from Other Image Registries in the Content Management Guide.

     Click Next to proceed.

4. In the Configuration stage of container creation, set the following parameters:

   • Provide the container name.
   • Specify a command to run inside the container.
   • Specify an entrypoint, which is a command that is executed automatically as soon as the container starts. The default entrypoint is /bin/sh -c.
   • Assign CPUs to the container. For example, 0-2,16 represents CPUs 0, 1, 2, and 16.
   • Define the relative share of CPU time for the container.

   • Specify a memory limit for the container. For example, 512m limits the container memory usage to 512 MB.

     Click Next to proceed.

5. In the final stage of container creation named Environment, select if you want to allocate a pseudo-tty, attach STDIN, STDOUT, and STDERR to the container. Click Add environment variable to create a custom environment variable for the container. Select the Run? check box to start the container automatically after it is created.
6. Click Submit to create the container.

To Investigate a Container:

1. Navigate to Containers > All Containers.
2. On the Containers page, every Docker compute resource has a dedicated tab. Each of these tabs contains the table of available containers together with selected parameters of each container. Select the tab of the compute resource you want to inspect.
3. To view the container metadata, click the name of the container you want to inspect. Satellite displays the table of container properties.
4. On the Processes tab, you can view processes that are currently running in the container. Click on the process name to view the metadata of the process.
5. If the container is running, you can view its standard output in the Logs tab. If you selected the allocate a pseudo-tty check box when creating a container, the console is interactive. Otherwise, it displays the initial standard output produced when the container started.

To Start or Stop a Container:

1. Navigate to Containers > All Containers to view the list of available containers.
2. Click Power On next to the container you want to start. After starting the container, the button changes to Power Off, which allows for stopping the container. These actions are equivalent to the docker start and docker stop commands.

To Commit a Container:

1. Navigate to Containers > All Containers to view the list of available containers.
2. Click the name of the container you want to commit.

3. Click Commit. Satellite prompts you to:

   • Specify a repository name. This can be a single name or combined with the user name, for example user/my-rhel-image.
   • Assign a tag to the image.
   • Provide your contact information.
   • Provide an informative comment about the image.
4. Click Submit.

To Remove a Container:

1. Navigate to Containers > All Containers to view the list of available containers.
2. Click the name of the container you want to delete.
3. Click Delete.
4. In the alert box, click OK to remove the container.