Skaffold’s integration with Google Cloud Build for remote image building is surprisingly more about managing build provenance and reproducibility than just offloading CPU-intensive Docker builds.
Let’s see it in action. Imagine you have a simple skaffold.yaml configured to use Cloud Build:
apiVersion: skaffold/v4beta10
kind: Config
build:
googleCloudBuild:
projectID: my-gcp-project-id
docker:
# You can optionally specify a custom builder image if needed
# builderImage: gcr.io/cloud-builders/docker
pipeline:
build:
artifacts:
- image: gcr.io/my-gcp-project-id/my-app
docker:
dockerfile: Dockerfile
When you run skaffold dev, Skaffold doesn’t just docker build and push. It orchestrates a sequence of events within Google Cloud Build. First, it uploads your entire build context (your application source code, Dockerfile, and any other files needed for the build) to a Cloud Storage bucket. Then, it triggers a Cloud Build job. This job pulls the specified builder image (e.g., gcr.io/cloud-builders/docker), executes the docker build command within its environment using the uploaded context, and tags the resulting image. Finally, Cloud Build pushes the image to your specified container registry (e.g., gcr.io). Skaffold then fetches the image digest and uses that for deploying to your Kubernetes cluster.
The core problem this solves is shifting the build environment from your local machine to a consistent, reproducible, and often faster cloud-based environment. This means developers don’t need powerful local machines with Docker installed and configured. More importantly, it ensures that the image built in CI/CD is the exact same image that was tested locally, eliminating the "it worked on my machine" syndrome. The build is tied to your GCP project, leveraging its IAM for authentication and its infrastructure for execution.
You control several key aspects:
projectID: This is fundamental. It tells Cloud Build which GCP project to use for the build job and where to push the resulting image.docker.builderImage: While often implicit, you can explicitly choose a different builder image if you have specific needs (e.g., a custom image with pre-installed tools).docker.dockerfile: Specifies the path to your Dockerfile relative to the build context.docker.buildArgs: You can pass arguments directly todocker buildvia this field, allowing for dynamic build-time configurations.docker.target: If your Dockerfile has multi-stage builds, you can specify which stage to build.
The mental model here is that Skaffold acts as an orchestrator, offloading the actual container image build to a managed service. It’s not just about convenience; it’s about ensuring build integrity.
What most people overlook is how Skaffold manages the build context. It doesn’t just send your Dockerfile; it packages up everything in your project directory by default, minus any files specified in a .dockerignore file, and uploads that entire archive. This ensures that any COPY or ADD commands in your Dockerfile that refer to local files will find them correctly within the Cloud Build environment.
The next concept you’ll grapple with is how to manage build secrets when using Cloud Build, especially for dependencies outside of your immediate source code.