add support for gcr registries

README.md

@@ -2,7 +2,7 @@
 
 A thin shim-wrapper around the official [Google Kaniko](https://cloud.google.com/blog/products/gcp/introducing-kaniko-build-container-images-in-kubernetes-and-google-container-builder-even-without-root-access) Docker image to make it behave like the [Drone Docker plugin](http://plugins.drone.io/drone-plugins/drone-docker/).
 
-Example .drone.yml for Drone 1.0
+Example .drone.yml for Drone 1.0 (pushing to Docker Hub):
 
 ```yaml
 kind: pipeline
@@ -25,6 +25,23 @@ steps:
       from_secret: docker-password
 ```
 
+Pushing to GCR:
+
+```yaml
+kind: pipeline
+name: default
+
+steps:
+- name: publish
+  image: banzaicloud/drone-kaniko
+  settings:
+    repo: gcr.io/example.com/example-project
+    tags: ${DRONE_COMMIT_SHA}
+    cache: true
+    google_application_credentials:
+      from_secret: google-application-credentials
+```
+
 ## Test that it can build
 
 ```bash
@@ -58,8 +75,14 @@ docker run -v $PWD:/cache gcr.io/kaniko-project/warmer:latest --verbosity=debug
 ```
 
 
-Run the builder on the host network to be able to access the registry and the local disk cache:
+Run the builder (on the host network to be able to access the registry, if any specified) with mounting the local disk cache, this example pushes to Docker Hub:
 
 ```bash
 docker run --net=host -it --rm -w /src -v $PWD:/cache -v $PWD:/src -e PLUGIN_USERNAME=${DOCKER_USERNAME} -e PLUGIN_PASSWORD=${DOCKER_PASSWORD} -e PLUGIN_REPO=banzaicloud/drone-kaniko-test -e PLUGIN_TAGS=test -e PLUGIN_DOCKERFILE=Dockerfile.test -e PLUGIN_CACHE=true banzaicloud/drone-kaniko
 ```
+
+The very same example just pushing to GCR instead of Docker Hub:
+
+```bash
+docker run --net=host -it --rm -w /src -v $PWD:/cache -v $PWD:/src -e PLUGIN_REPO=gcr.io/banzaicloud/drone-kaniko-test -e PLUGIN_TAGS=test -e PLUGIN_DOCKERFILE=Dockerfile.test -e PLUGIN_CACHE=true -e PLUGIN_GOOGLE_APPLICATION_CREDENTIALS="$(<$HOME/google-application-credentials.json)" banzaicloud/drone-kaniko
+```

plugin.sh

@@ -4,11 +4,12 @@ set -euo pipefail
 
 export PATH=$PATH:/kaniko/
 
-DOCKER_AUTH=`echo -n "${PLUGIN_USERNAME}:${PLUGIN_PASSWORD}" | base64 | tr -d "\n"`
+if [ "${PLUGIN_USERNAME:-}" ] || [ "${PLUGIN_PASSWORD:-}" ]; then
+    DOCKER_AUTH=`echo -n "${PLUGIN_USERNAME}:${PLUGIN_PASSWORD}" | base64 | tr -d "\n"`
 
-REGISTRY=${PLUGIN_REGISTRY:-https://index.docker.io/v1/}
+    REGISTRY=${PLUGIN_REGISTRY:-https://index.docker.io/v1/}
 
-cat > /kaniko/.docker/config.json <<DOCKERJSON
+    cat > /kaniko/.docker/config.json <<DOCKERJSON
 {
     "auths": {
         "${REGISTRY}": {
@@ -17,6 +18,12 @@ cat > /kaniko/.docker/config.json <<DOCKERJSON
     }
 }
 DOCKERJSON
+fi
+
+if [ "${PLUGIN_GOOGLE_APPLICATION_CREDENTIALS:-}" ];then
+    echo "${PLUGIN_GOOGLE_APPLICATION_CREDENTIALS}" > /kaniko/gcr.json
+    export GOOGLE_APPLICATION_CREDENTIALS=/kaniko/gcr.json
+fi
 
 DOCKERFILE=${PLUGIN_DOCKERFILE:-Dockerfile}
 CONTEXT=${PLUGIN_CONTEXT:-$PWD}