Chapter 4. Creating a fully self-contained bootc image

Procedure

1. Add the pull secret to the container build procedure to ensure that images can be pulled by running the following command:

   $ podman build --secret id=pullsecret,src=/<path/to/pull/secret>.json 

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   Specify the path to your pull secret in <path/to/pull/secret>.

2. Add the instructions to physically embed the image at build time by adding the following to your Containerfile:

   ENV IMAGE_STORAGE_DIR=/usr/lib/containers/storage
   ENV IMAGE_LIST_FILE=${IMAGE_STORAGE_DIR}/image-list.txt
   
   RUN dnf install -y microshift-release-info
   RUN --mount=type=secret,id=pullsecret,dst=/run/secrets/pull-secret.json \
       images="$(jq -r ".images[]" /usr/share/microshift/release/release-"$(uname -m)".json)" ; \
       mkdir -p "${IMAGE_STORAGE_DIR}" ; \
       for img in ${images} ; do \
           sha="$(echo "${img}" | sha256sum | awk '{print $1}')" ; \
           skopeo copy --all --preserve-digests \
               --authfile /run/secrets/pull-secret.json \
               "docker://${img}" "dir:$IMAGE_STORAGE_DIR/${sha}" ; \
           echo "${img},${sha}" >> "${IMAGE_LIST_FILE}" ; \
       done

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   When run, the Containerfile extracts the list of MicroShift container image dependencies from the microshift-release-info RPM and pulls them into a custom /usr/lib/containers/storage directory. The resulting image list file is saved at /usr/lib/containers/storage/image-list.txt.

3. Next, you must copy container images from the custom directory to the main container storage directory so that they are available to MicroShift. Add a script and a systemd service to your Containerfile to copy the embedded images from the /usr/lib/containers/storage directory to the local container storage. Copying happens at runtime before each MicroShift start. Use the following example:

   RUN cat > /usr/bin/microshift-copy-images <<EOF
   #!/bin/bash
   set -eux -o pipefail
   while IFS="," read -r img sha ; do
       skopeo copy --preserve-digests \
           "dir:${IMAGE_STORAGE_DIR}/\${sha}" \
           "containers-storage:\${img}"
   done < "${IMAGE_LIST_FILE}"
   EOF
   
   RUN chmod 755 /usr/bin/microshift-copy-images && \
       mkdir -p /usr/lib/systemd/system/microshift.service.d
   
   RUN cat > /usr/lib/systemd/system/microshift.service.d/microshift-copy-images.conf <<EOF
   [Service]
   ExecStartPre=/usr/bin/microshift-copy-images
   EOF

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Next steps

1. Build the image.
2. Test and deploy per your use case.