Continuous Development

When developing on Kubernetes, it can be time-consuming to manually run commands to build new images, push images to a container registry, update Kubernetes manifests, and deploy new manifests to the cluster with each source-code change.

Skaffold is a tool that can be used to ease this process. Skaffold will automate the process of building, pushing and deploying new images based on changes to the source-code.

Skaffold requires minimal setup as the tool has no cluster-side components, and will automatically detect the configuration to use.

Installing Skaffold

The Skaffold CLI can be installed by downloading and installing the latest release. Instructions can be found in the Skaffold documentation:

curl -Lo skaffold https://storage.googleapis.com/skaffold/releases/v2.0.1/skaffold-linux-amd64 && \
sudo install skaffold /usr/local/bin/

Getting started with Skaffold

Note

Skaffold will use the active KUBECONFIG to authenticate to the Kubernetes cluster.

If you haven't done so already, clone the user demo:

git clone https://github.com/elastisys/welkin/
cd welkin/user-demo

Initialize Skaffold

skaffold init

This command will scan the current project for images to build and Kubernetes manifests to deploy. For each image that Skaffold finds you will be prompted to specify how to build them, or if they are not built by the current project.

The first image Skaffold finds is busybox, however this image is not built from this project, so choose: None (image not built from these sources)

The second image Skaffold finds is the user-demo image and this image is built from the Dockerfile.

Skaffold then asks for which resources we want to create Kubernetes resources, but as the image already has a Helm Chart this can be skipped by pressing enter.

Skaffold will then create the skaffold.yaml file containing our configuration. Skaffold will also automatically detect the Helm Chart that deploys the user-demo image.

The skaffold.yaml must then be configured to use the correct domain and project for the image (More info). You need push access to this repository (Optionally add a hostname to access the application).

build:
  artifacts:
- - image: i-didnt-read-the-docs/welkin-user-demo
+ - image: <DOMAIN>/<REGISTRY_PROJECT>/welkin-user-demo
    docker:
      dockerfile: Dockerfile
...
  valuesFiles:
  - deploy/welkin-user-demo/values.yaml
  version: 0.1.0
+ setValues:
+   image.repository: <DOMAIN>/<REGISTRY_PROJECT>/welkin-user-demo
+   ingress.hostname: demo.<DOMAIN>     # (Optional)

If the repository is private, a pull secret must be created to use it in Kubernetes, see Configure an Image Pull Secret.

Developing

To start developing using Skaffold run:

skaffold dev

When you run skaffold dev, Skaffold will first build, and deploy all of the artifacts specified in skaffold.yaml. Skaffold will then begin monitoring all source file dependencies for all artifacts specified in the project and rebuild the associated artifacts and redeploy the new changes to your cluster as changes are made to these source files. So any changes made to the source-files will automatically be updated in the cluster.

When starting skaffold dev, the logs of the deployed artifacts will automatically be directed to the console, which makes it easy to debug the application in the cluster.

If ingress.hostname was configured previously the application can be accessed from there directly. Otherwise the flag --port-forward can be added to the command, and Skaffold will automatically forward the ports on the application to the local workstation:

skaffold dev --port-forward

Application updates

When the application has been built and deployed to the cluster Skaffold shows which URL to access, shows the logs of the application, and starts listening for changes in the source-files.

When visiting the URL to the application or the port-forwarded URL the following output can be seen:

{ "hostname": "welkin-user-demo-dd9c58979-rm9rv", "version": "0.0.1" }

If you inside the routes/index.js file add the following:

...
res.send({
  hostname: os.hostname(),
  version: process.env.npm_package_version,
+ hello: "world"
});
...

And then save the file, Skaffold will automatically detect the change, build a new image, and deploy the new image to the cluster. After the deployment has stabilized, when visiting the same URL, the output is now:

{ "hostname": "welkin-user-demo-54bbdcf6fc-gthsc", "version": "0.0.1", "hello": "world" }

Configuration updates

To see the amount of pods, run (inside another terminal):

$ kubectl get pods
NAME                              READY   STATUS    RESTARTS   AGE
welkin-user-demo-7645db4f5c-h4xks   1/1     Running   0          45s
welkin-user-demo-7645db4f5c-svqfs   1/1     Running   0          35s

There are two pods running. To change this, edit the file deploy/welkin-user-demo/values.yaml:

- replicaCount: 2
+ replicaCount: 1

And save the file, this will also trigger Skaffold to update the deployment. Because the modification only impacts the Kubernetes configuration, the application image does not need to be rebuilt, and a new Helm revision may be deployed right away.

Once the deployments have stabilized the amount of pods can be inspected again:

$ kubectl get pods
NAME                              READY   STATUS    RESTARTS   AGE
welkin-user-demo-7645db4f5c-svqfs   1/1     Running   0          4m45s

Clean-up

To stop Skaffold ctrl + c can be used and will trigger Skaffold to stop listening for changes and clean-up the deployed artifacts from the cluster.

The clean-up can also be triggered by running:

skaffold delete

Advanced

• Skaffold supports multiple different builder, such as Dockerfile, Bazel, Buildpacks or others (More Info).

• Skaffold supports copying files to the running containers which will avoid rebuilding of containers when not needed (More Info).

Further Reading

• Skaffold Documentation