Red Hat OpenShift Development I: Introduction to Containers with Podman

Instructions

1. Examine the exercise application.

   1. Navigate to the ~/DO188/labs/custom-advanced directory.

      [student@workstation ~]$ cd ~/DO188/labs/custom-advanced
      no output expected

   2. Examine the main.py file, which contains a basic Python application. The application reads the numbers.txt file, prints its content, and appends another number to the file. The application uses an environment variable to locate the numbers.txt file.

      ...output omitted...
      
      FILE = environ.get('FILE')
      
      ...output omitted...

   3. Examine the incomplete Containerfile file.

2. Use a multistage build to complete the Containerfile file.

   Add a stage that uses the registry.ocp4.example.com:8443/redhattraining/podman-random-numbers base image. The base image contains the random_generator.py script. Use the script to generate a numbers.txt file and copy the file to the final stage.

   1. Create a stage by adding a FROM instruction.

      FROM registry.ocp4.example.com:8443/redhattraining/podman-random-numbers as generator
      
      FROM registry.ocp4.example.com:8443/ubi8/python-38:1-96
      ...output omitted...

   2. Generate the numbers.txt file.

      FROM registry.ocp4.example.com:8443/redhattraining/podman-random-numbers as generator
      RUN python3 random_generator.py
      
      FROM registry.ocp4.example.com:8443/ubi8/python-38:1-96
      ...output omitted...

   3. In the second build stage, copy the numbers.txt file by using the --from=generator option of the COPY instructon. Use the --chown option to make the user default the new owner.

      ...output omitted...
      WORKDIR /redhat
      
      COPY --from=generator --chown=default /app/numbers.txt materials/numbers.txt
      COPY main.py .
      ...output omitted...

3. Add the FILE environment variable to set the path of the numbers.txt file.

   FROM registry.ocp4.example.com:8443/redhattraining/podman-random-numbers as generator
   RUN python3 random_generator.py
   
   FROM registry.ocp4.example.com:8443/ubi8/python-38:1-96
   
   ENV FILE="/redhat/materials/numbers.txt"
   USER default
   WORKDIR /redhat
   
   COPY --from=generator --chown=default /app/numbers.txt materials/numbers.txt
   COPY main.py .
   
   CMD python3 main.py

4. Build and test the image.

   1. In a command-line terminal, build the image from the Containerfile.

      [student@workstation custom-advanced]$ podman build -t \
       redhat-local/custom-advanced .
      ...output omitted...
      Successfully tagged localhost/redhat-local/custom-advanced:latest
      3360...cc21

   2. Run the image.

      [student@workstation custom-advanced]$ podman run --rm \
       --name=custom-advanced redhat-local/custom-advanced
      Current content: ['17 72 97 8 32 15 63 97 57']
      Writing another number...
      Current content: ['17 72 97 8 32 15 63 97 57 4']

      The application uses the environment variable to read from the file, and write content to the file. The numbers that you get might differ because they are generated randomly, however, a 4 is always appended to the end.

5. Add a mount point to the /redhat/materials directory.

   1. In the Containerfile, add a VOLUME instruction.

      ...output omitted...
      COPY main.py .
      
      VOLUME /redhat/materials
      
      CMD python3 main.py

6. Build and test the image.

   1. In your command-line terminal, build the image from the Containerfile.

      [student@workstation custom-advanced]$ podman build -t \
       redhat-local/custom-advanced .
      ...output omitted...
      Successfully tagged localhost/redhat-local/custom-advanced:latest
      4872...0ee0

   2. Create a container from the image.

      [student@workstation custom-advanced]$ podman run --name=custom-advanced \
        redhat-local/custom-advanced
      Current content: ['46 37 98 39 70 53 81 44 59']
      Writing another number...
      Current content: ['46 37 98 39 70 53 81 44 59 4']

      Note

      The previous command does not have the --rm option. If you use the --rm option, then Podman removes the anonymous volumes that the container uses.

7. Read the numbers.txt file on your local file system.

   1. Inspect the container to identify the anonymous volume path on the file system.

      [student@workstation custom-advanced]$ podman inspect custom-advanced
      ...output omitted...
        "Mounts": [
             {
                  "Type": "volume",
                  "Name": "3aa7...22ac",
                  "Source": "/home/student/.local/share/containers/storage/volumes/3aa7...22ac/_data",
                  "Destination": "/redhat/materials",
                  "Driver": "local",
      ...output omitted...

      You can limit the output of the podman inspect command by using the --format option.

      [student@workstation custom-advanced]$ podman inspect custom-advanced \
       --format="{{ (index .Mounts 0).Source}}"
      /home/student/.local/share/containers/storage/volumes/40ed...96bf/_data

   2. Use the Source path to read the numbers.txt file from your local file system.

      [student@workstation custom-advanced]$ cat SOURCE/numbers.txt
      46 37 98 39 70 53 81 44 59 4