Chapter 20. Working with containers using Buildah

Procedure

1. Create a working container based on the registry.access.redhat.com/ubi8/ubi image and save the name of the container to the mycontainer variable:

   # mycontainer=$(buildah from localhost/myecho)
   
   # echo $mycontainer
   myecho-working-container

2. Mount the myecho-working-container container and save the mount point path to the mymount variable:

   # mymount=$(buildah mount $mycontainer)
   
   # echo $mymount
   /var/lib/containers/storage/overlay/c1709df40031dda7c49e93575d9c8eebcaa5d8129033a58e5b6a95019684cc25/merged

3. Modify the myecho script and make it executable:

   # echo 'echo "We modified this container."' >> $mymount/usr/local/bin/myecho
   # chmod +x $mymount/usr/local/bin/myecho

4. Create the myecho2 image from the myecho-working-container container:

   # buildah commit $mycontainer containers-storage:myecho2

Verification

1. List all images in local storage:

   # buildah images
   REPOSITORY                                  TAG      IMAGE ID       CREATED          SIZE
   docker.io/library/myecho2                   latest   4547d2c3e436   4 minutes ago    234 MB
   localhost/myecho                            latest   b28cd00741b3   56 minutes ago   234 MB

2. Run the myecho2 container based on the docker.io/library/myecho2 image:

   # podman run --name=myecho2 docker.io/library/myecho2
   This container works!
   We even modified it.

Procedure

1. Create a script named newecho and make it executable:

   # cat newecho
   echo "I changed this container"
   # chmod 755 newecho

2. Create a new working container:

   # buildah from myecho:latest
   myecho-working-container-2

3. Copy the newecho script to /usr/local/bin directory inside the container:

   # buildah copy myecho-working-container-2 newecho /usr/local/bin

4. Change the configuration to use the newecho script as the new entrypoint:

   # buildah config --entrypoint "/bin/sh -c /usr/local/bin/newecho" myecho-working-container-2

5. Optional: Run the myecho-working-container-2 container whixh triggers the newecho script to be executed:

   # buildah run myecho-working-container-2 -- sh -c '/usr/local/bin/newecho'
   I changed this container

6. Commit the myecho-working-container-2 container to a new image called mynewecho:

   # buildah commit myecho-working-container-2 containers-storage:mynewecho

Procedure

1. Create the local registry on your machine:

   # podman run -d -p 5000:5000 registry:2

2. Push the myecho:latest image to the localhost registry:

   #  buildah push --tls-verify=false myecho:latest localhost:5000/myecho:latest
   Getting image source signatures
   Copying blob sha256:e4efd0...
   ...
   Writing manifest to image destination
   Storing signatures

Verification

1. List all images in the localhost repository:

   # curl http://localhost:5000/v2/_catalog
   {"repositories":["myecho2]}
   
   
   # curl http://localhost:5000/v2/myecho2/tags/list
   {"name":"myecho","tags":["latest"]}

2. Inspect the docker://localhost:5000/myecho:latest image:

   # skopeo inspect --tls-verify=false docker://localhost:5000/myecho:latest | less
   {
       "Name": "localhost:5000/myecho",
       "Digest": "sha256:8999ff6050...",
       "RepoTags": [
           "latest"
       ],
       "Created": "2021-06-28T14:44:05.919583964Z",
       "DockerVersion": "",
       "Labels": {
           "architecture": "x86_64",
           "authoritative-source-url": "registry.redhat.io",
       ...
   }

3. Pull the localhost:5000/myecho image:

   # podman pull --tls-verify=false localhost:5000/myecho2
   # podman run localhost:5000/myecho2
   This container works!

Procedure

1. Push the docker.io/library/myecho:latest to your Docker Hub. Replace username and password with your Docker Hub credentials:

   # buildah push --creds username:password \
     docker.io/library/myecho:latest docker://testaccountXX/myecho:latest

Procedure

1. List all containers:

   # buildah containers
   CONTAINER ID  BUILDER  IMAGE ID     IMAGE NAME                       CONTAINER NAME
   05387e29ab93     *     c37e14066ac7 docker.io/library/myecho:latest  myecho-working-container

2. Remove the myecho-working-container container:

   # buildah rm myecho-working-container
   05387e29ab93151cf52e9c85c573f3e8ab64af1592b1ff9315db8a10a77d7c22