An example of how to build an rootfs tgz suitable for use in concourse with `image_resource` set to `type: s3`

example-pipeline.yml

---
resources:
- name: source
  type: git
  source:
    uri: {{git-uri}}
    branch: {{git-branch}}
    private_key: {{git-private-key}}

- name: s3
  type: s3
  source:
    access_key_id: {{s3-access-key-id}}
    bucket: {{s3-bucket}}
    secret_access_key: {{s3-secret-access-key}}
    region_name: {{s3-region}}
    regexp: my-example-image-(.*).tar.gz

- name: version
  type: semver
  source:
    access_key_id: {{s3-access-key-id}}
    region_name: {{s3-region}}
    bucket: {{s3-bucket}}
    secret_access_key: {{s3-secret-access-key}}
    key: my-example-image-version
    initial_version: 0.0.0

jobs:
- name: build-image
  plan:
  - aggregate:
    - get: source
      trigger: true
    - get: version
      params: {bump: patch}
  - task: build-image
    privileged: true
    config:
      platform: linux
      inputs:
      - name: source
      - name: version
      outputs:
      - name: s3-staging
      image_resource:
        type: docker-image
        source:
          repository: concourse/docker-image-resource
      run:
        path: sh
        args:
        - -ec
        - |
          base=$(pwd)
          cidfile=/tmp/container.id

          source /opt/resource/common.sh
          start_docker

          docker build source
          image_id=$(docker images | grep -v REPOSITORY | head -n1 | awk '{print $3}')

          mkdir export-dir && cd export-dir
          mkdir rootfs

          docker run --cidfile=${cidfile} \
             -v /opt/resource/print-metadata:/tmp/print-metadata \
             --entrypoint /tmp/print-metadata  \
             ${image_id} > metadata.json
         
          docker export $(cat ${cidfile}) | tar --exclude="dev/*" -xf - -C ./rootfs/

          cd ${base}/s3-staging
          tar -czf my-example-image-$(cat ${base}/version/version).tar.gz -C ${base}/export-dir .
  - put: s3
    params: {file: s3-staging/my-example-image-*.tar.gz}
  - put: version
    params: {file: version/version}