cloud_build_config.yaml

# This file should live adjacent to the my_target directory.
# To use:
# Submit the build:
# $ gcloud builds submit --timeout=1h --config cloud_build_config.yaml . --project YOUR_PROJECT_NAME

steps:
- name: 'gcr.io/cloud-builders/docker'
  args: ['build',
          '-t', 'gcr.io/$PROJECT_ID/example-image-for-pod-operator:latest',
          'my_target']
  id: 'my-target'
images:
- 'gcr.io/$PROJECT_ID/example-image-for-pod-operator:latest'

Dockerfile

# This file belongs in the my_target directory.
# Start from a base image you like.
FROM gcr.io/google-appengine/python

# Run ordinary commands to set up the environment the way you like.
# Read more about Docker to see what else you can do here.
RUN pip install NumPy
USER root
RUN mkdir -p /var/local
COPY startup.sh /var/local
RUN chmod +x /var/local/startup.sh

# This will be the command that is run by this image by default.
CMD ["bash", "-c", "/var/local/startup.sh"]

startup.sh

# This file belongs in the my_target directory.
echo "Hello World"