Deploy a new image from Google Cloud Container Builder to Kubernetes, by storing GKE credentials in GCS.

gcb-kubernetes.yaml

steps:
- name: 'gcr.io/cloud-builders/npm'
  args: ['install']
- name: 'gcr.io/cloud-builders/npm'
  args: ['test']
- name: 'gcr.io/cloud-builders/docker'
  args: ["build", "-t", "gcr.io/$PROJECT_ID/frontend:$REVISION_ID", "."]
- name: 'gcr.io/cloud-builders/docker'
  args: ["push", "gcr.io/$PROJECT_ID/frontend:$REVISION_ID"]
- name: 'gcr.io/cloud-builders/gcloud'
  entrypoint: 'bash'
  args:
  - '-c'
  - |
    gcloud components install kubectl
    gsutil cp gs://container-kubernetes-key/kubeconfig .
    export KUBECONFIG=kubeconfig
    kubectl set image deployment/frontend frontend=gcr.io/$PROJECT_ID/frontend:$REVISION_ID

How do you actually get the kubeconfig file into the cloud storage? / how do you create that file so the script is able to connect to the k8s cluster?

gsutil cp ~/.kube/config gs://container-kubernetes-key/kubeconfig

You don't need this magic anymore: https://github.com/GoogleCloudPlatform/cloud-builders/blob/master/kubectl/examples/pods-list/cloudbuild.yaml

I took an "upside-down" approach to this problem and made this tool: https://github.com/dminkovsky/kube-cloud-build/

Also, do take a look at http://github.com/weaveworks/flux, it offers a more decoupled approach with where you install a git reconciliation operator into your cluster, and it picks up new images from the registry, makes changes in git and then applies new config to the cluster.
We blogged a lot about our approach too, see e.g. https://www.weave.works/blog/gitops-high-velocity-cicd-for-kubernetes.

I keep hitting this error:

Step #2: ERROR: (gcloud.container.clusters.get-credentials) ResponseError: code=403, message=Required "container.clusters.get" permission for "projects/buildanything-io/zones/us-central1-a/clusters/cluster-3".
Finished Step #2
ERROR
ERROR: build step 2 "gcr.io/cloud-builders/kubectl" failed: exit status 1

What shall I do?

@Philmod I am facing below issue which is similar to the above one.

The connection to the server localhost:8080 was refused - did you specify the right host or port?
ERROR: (gcloud.container.clusters.get-credentials) ResponseError: code=403, message=Required "container.clusters.get" permission for "projects/PROJECT/zones/ZONE/clusters/CLUSTER_NAME".
Fetching cluster endpoint and auth data.
All components are up to date.

Already have image (with digest): gcr.io/cloud-builders/gcloud

When you get Required "BLABLABLABLA" permission .... message, go into IAM -> Roles -> Create role [ROLE_NAME] -> add container.clusters.get and/or whatever other permissions you need in order to get it done, and assign that role (IAM -> Add) to the Cloud Builder service account ..........@cloudbuild.gserviceaccount.com

Secondly, it works with:

- id: kubectl-set-image
  name: gcr.io/cloud-builders/kubectl
  args: ['set', 'image', 'deployment/[DEPLOYMENT_NAME]', '[IMAGE_NAME]=gcr.io/$PROJECT_ID/[IMAGE_NAME]:$TAG_NAME']
  env:
  - 'CLOUDSDK_COMPUTE_ZONE=[ZONE]'
  - 'CLOUDSDK_CONTAINER_CLUSTER=[CLUSTER]'

The previous comment worked for me! Thanks for that.