Red Hat OpenShift Development I: Introduction to Containers with Podman

Instructions

1. Examine the source code of the applications.

   1. Navigate to the ~/DO188/labs/basics-exposing directory, where the applications are available.

      [student@workstation ~]$ cd ~/DO188/labs/basics-exposing
      no output expected

   2. View the contents of the podman-info-times/app/main.go file.

      [student@workstation basics-exposing]$ cat podman-info-times/app/main.go
      ...output omitted...
        http.ListenAndServe(":8080", r)
      ...output omitted...

      The application exposes an HTTP server on port 8080 that returns the current time for a city.

   3. Examine the Containerfile for the times application.

      [student@workstation basics-exposing]$ cat podman-info-times/Containerfile
      FROM registry.access.redhat.com/ubi8/go-toolset:1.17.7 as build
      WORKDIR /app
      USER root
      COPY app .
      RUN go build
      
      FROM registry.access.redhat.com/ubi8/ubi-minimal:8.5
      WORKDIR /app
      COPY --from=build /app/times-app .
      EXPOSE 8080
      ENTRYPOINT ["/app/times-app"]

      The registry.ocp4.example.com:8443/redhattraining/podman-info-times container image is based on this Containerfile.

   4. View the podman-info-cities/app/main.go file.

      [student@workstation basics-exposing]$ cat podman-info-cities/app/main.go
      ...output omitted...
        http.ListenAndServe(":8090", r)
      ...output omitted...

      The application exposes an HTTP server on port 8090 that returns information for a city.

   5. Examine the Containerfile for the cities application.

      [student@workstation basics-exposing]$ cat podman-info-cities/Containerfile
      FROM registry.access.redhat.com/ubi8/go-toolset:1.17.7 as build
      WORKDIR /app
      USER root
      COPY app .
      RUN go build
      
      FROM registry.access.redhat.com/ubi8/ubi-minimal:8.5
      WORKDIR /app
      COPY --from=build /app/cities-app .
      EXPOSE 8090
      ENTRYPOINT ["/app/cities-app"]

      The registry.ocp4.example.com:8443/redhattraining/podman-info-cities container image is based on this Containerfile.

   6. Navigate to the home directory. The rest of the exercise does not involve local files.

      [student@workstation basics-exposing]$ cd ~
      no output expected

2. Create a Podman network with DNS enabled.

   1. Observe that DNS is disabled in the default Podman network.

      [student@workstation ~]$ podman network inspect podman
      ...output omitted...
          "dns_enabled": false,
      ...output omitted...

   2. Create a network by using the podman network create command.

      [student@workstation ~]$ podman network create cities
      cities

   3. Inspect the cities network to verify that DNS is enabled.

      [student@workstation ~]$ podman network inspect cities
      ...output omitted...
          "dns_enabled": true,
      ...output omitted...

3. Start and test the times application attached to the cities network.

   1. Create a container for the times application that forwards port 8080 from the container to the host. Attach the container to the cities network.

      [student@workstation ~]$ podman run --name times-app \
      --network cities -p 8080:8080 -d \
      registry.ocp4.example.com:8443/redhattraining/podman-info-times:v0.1
      ...output omitted...
      256...ee0

   2. Inspect the times-app container to find its private IP within the Podman network and copy the IP address.

      [student@workstation ~]$ podman inspect times-app \
      -f '{{.NetworkSettings.Networks.cities.IPAddress}}'
      10.89.1.2

      Note

      If the name of the network includes characters such as a dash (-), then the preceding command will not work. To retrieve the IP address of the container attached to such a network, you must use alternative methods to limit the output of the podman inspect command. For example, the grep or jq tools can search or parse the output, respectively.

   3. Use the private IP address to make a request to the /times API endpoint from another container. Run the curl command inside a ubi-minimal container to fetch the current time for Bangkok, which has the code BKK. Attach the container to the cities network.

      Replace IP_ADDRESS with the IP address from the previous step.

      [student@workstation ~]$ podman run --rm --network cities \
      registry.ocp4.example.com:8443/ubi8/ubi-minimal:8.5 \
      curl -s http://IP_ADDRESS:8080/times/BKK && echo
      2022-06-28T19:59:55.241Z

      Note

      Without providing arguments, the echo command prints a new line character, which improves the output formatting.

   4. Use the DNS name to make a request to the /times API endpoint from another container.

      [student@workstation ~]$ podman run --rm --network cities \
      registry.ocp4.example.com:8443/ubi8/ubi-minimal:8.5 \
      curl -s http://times-app:8080/times/BKK && echo
      2022-06-28T20:04:37.241Z

      Note that times-app is used as the hostname instead of the IP address.

4. Start and test the cities application attached to the cities network.

   1. Create a container called cities-app and start the application on port 8090. Attach the container to the cities network.

      Set the TIMES_APP_URL environment variable to the URL of the times application. Notice that the URL uses the name of the times-app container.

      [student@workstation ~]$ podman run --name cities-app \
      --network cities -p 8090:8090 -d \
      -e TIMES_APP_URL=http://times-app:8080/times \
      registry.ocp4.example.com:8443/redhattraining/podman-info-cities:v0.1
      ...output omitted...
      dcc...1fd

   2. Fetch the city information of Madrid by using the MAD city code.

      [student@workstation ~]$ curl -s http://localhost:8090/cities/MAD | jq
      {
        "name": "Madrid",
        "time": "2022-06-01T12:34:56.123Z",
        "population": 3223000,
        "country":"Spain"
      }

      Note

      Passing the output of the curl command to the jq command provides better formatting of the JSON response compared to viewing the raw output.

   3. Fetch the city information of San Diego by using the SAN city code.

      [student@workstation ~]$ curl -s http://localhost:8090/cities/SAN | jq
      {
        "name": "San Diego",
        "time": "2022-06-01T12:34:56.123Z",
        "population": 1415000,
        "country": "United States of America"
      }