Red Hat OpenShift Development I: Introduction to Containers with Podman

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Lab: Persisting Data

Use volumes to provide persistence to an application.

Outcomes

You should be able to create volumes, import data into volumes, and use volumes in an application.

This lab uses a URL shortener application, which consists of three components: a database container, a back-end container, and a front-end container.

The source code for the front end and back end is available at ~/DO188/solutions/persisting-lab after you execute the lab script.

Note the following:

  • The back-end container uses the following information:

    • The back end uses default values for the user, password, and database for simplicity.

    • The back end uses the database container name to resolve the database IP address. Do not change the database container name.

  • The front-end container uses the following information:

    • The front end uses an Nginx server to redirect requests from localhost:8080 to the persisting-backend:8080 host. Do not change the back-end container name.

    • If the front end exits after start, execute podman logs persisting-frontend to check the logs.

  • The application can become unresponsive after you stop individual containers. If this happens, stop all containers and start the containers in order of database, back end, and front end.

As the student user on the workstation machine, use the lab command to prepare your system for this exercise.

[student@workstation ~]$ lab start persisting-lab

The lab script continuously evaluates the objectives of this lab. Keep the script running in a terminal window and complete the objectives of this lab from a new terminal window.

Instructions

  1. Create a named volume with the following parameters:

    • The volume is called postgres-vol.

    • The volume contains the contents of the ~/DO188/labs/persisting-lab/postgres-vol.tar.gz file.

    1. Create the volume.

      [student@workstation ~]$ podman volume create postgres-vol
postgres-vol

    2. Import the ~/DO188/labs/persisting-lab/postgres-vol.tar.gz file to the volume:

      [student@workstation ~]$ podman volume import postgres-vol \
~/DO188/labs/persisting-lab/postgres-vol.tar.gz
...no output expected...

  2. Start the application database container with the following parameters:

    • Call the container persisting-db.

    • Start the container in the background.

    • Connect the container to the persisting-net network.

    • Use the following environment variables:

      • POSTGRESQL_PASSWORD=pass

      • POSTGRESQL_USER=user

      • POSTGRESQL_DATABASE=db

    • Mount the postgres-vol volume to the /var/lib/pgsql/data directory.

    • Use the registry.ocp4.example.com:8443/rhel9/postgresql-13:1 image.

    1. Create the persisting-net network.

      [student@workstation ~]$ podman network create persisting-net
persisting-net

    2. Start the database container.

      [student@workstation ~]$ podman run --name persisting-db -d \
 --net persisting-net -e POSTGRESQL_USER=user -e POSTGRESQL_PASSWORD=pass \
 -e POSTGRESQL_DATABASE=db \
 --mount='type=volume,src=postgres-vol,dst=/var/lib/pgsql/data' \
 registry.ocp4.example.com:8443/rhel9/postgresql-13:1
c97f...4a29

  3. Start the back end with the following parameters:

    • Call the container persisting-backend.

    • Start the container in the background.

    • Use the environment variable DB_HOST=persisting-db.

    • Expose the port 8080 on the machine to route requests to port 8080 inside the container.

    • Connect the container to the persisting-net network.

    • Use the registry.ocp4.example.com:8443/redhattraining/podman-urlshortener-backend image.

    [student@workstation ~]$ podman run --name persisting-backend -d \
 -e DB_HOST=persisting-db -p 8080:8080 --net persisting-net \
 registry.ocp4.example.com:8443/redhattraining/podman-urlshortener-backend
3a46...4e60

  4. Start the front end with the following parameters:

    • Call the container persisting-frontend.

    • Start the container in the background.

    • Connect the container to the persisting-net network.

    • Expose the port 3000 on the machine to route requests to port 8080 inside the container.

    • Use the registry.ocp4.example.com:8443/redhattraining/podman-urlshortener-frontend image.

    [student@workstation ~]$ podman run --name persisting-frontend -d \
  --net persisting-net -p 3000:8080 \
  registry.ocp4.example.com:8443/redhattraining/podman-urlshortener-frontend
b10e...940f

  5. Test the application.

    1. In a web browser, verify the functionality of the application at http://localhost:3000.

    2. In a web browser, test the database data import by navigating to http://localhost:8080/api/shorturl/a9yi4rcl5uuzunv.

      The a9yi4rcl5uuzunv short URL is a part of the database data that you imported in a previous step into the postgres-vol volume.

Finish

As the student user on the workstation machine, use the lab command to complete this exercise. This is important to ensure that resources from previous exercises do not impact upcoming exercises.

Press y when the lab start command prompts you to execute the finish function. Alternatively, execute the following command:

[student@workstation ~]$ lab finish persisting-lab

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Revision: do188-4.14-8c43a16