Add GCP pubsub docs (#446)

howto/setup-pub-sub-message-broker/README.md

@@ -46,3 +46,4 @@ kubectl apply -f pubsub.yaml
 - [Setup NATS](./setup-nats.md)
 - [Setup Azure Service bus](./setup-azure-servicebus.md)
 - [Setup RabbitMQ](./setup-rabbitmq.md)
+- [Setup GCP Pubsub](./setup-gcp.md)

howto/setup-pub-sub-message-broker/setup-gcp.md

@@ -0,0 +1,72 @@
+# Setup GCP Pubsub
+
+Follow the instructions [here](https://cloud.google.com/pubsub/docs/quickstart-console) on setting up Google Cloud Pub/Sub system.
+
+## Create a Dapr component
+
+The next step is to create a Dapr component for Google Cloud Pub/Sub
+
+Create the following YAML file named `messagebus.yaml`:
+
+```yml
+apiVersion: dapr.io/v1alpha1
+kind: Component
+metadata:
+  name: <NAME>
+spec:
+  type: pubsub.gcp.pubsub
+  metadata:
+  - name: topic
+    value: <TOPIC_NAME>
+  - name: type
+    value: service_account
+  - name: project_id
+    value: <PROJECT_ID> # replace
+  - name: private_key_id
+    value: <PRIVATE_KEY_ID> #replace
+  - name: client_email
+    value: <CLIENT_EMAIL> #replace
+  - name: client_id
+    value: <CLIENT_ID> # replace
+  - name: auth_uri
+    value: https://accounts.google.com/o/oauth2/auth
+  - name: token_uri
+    value: https://oauth2.googleapis.com/token
+  - name: auth_provider_x509_cert_url
+    value: https://www.googleapis.com/oauth2/v1/certs
+  - name: client_x509_cert_url
+    value: https://www.googleapis.com/robot/v1/metadata/x509/<PROJECT_NAME>.iam.gserviceaccount.com
+  - name: private_key
+    value: <PRIVATE_KEY> # replace x509 cert here
+  - name: disableEntityManagement
+    value: <REPLACE-WITH-DISABLE-ENTITY-MANAGEMENT> # Optional. Default: false. When set to true, topics and subscriptions do not get created automatically.
+```
+
+- `topic` is the Pub/Sub topic name.
+- `type` is the GCP credentials type.
+- `project_id` is the GCP project id.
+- `private_key_id` is the GCP private key id.
+- `client_email` is the GCP client email.
+- `client_id` is the GCP client id.
+- `auth_uri` is Google account OAuth endpoint.
+- `token_uri` is Google account token uri.
+- `auth_provider_x509_cert_url` is the GCP credentials cert url.
+- `client_x509_cert_url` is the GCP credentials project x509 cert url.
+- `private_key` is the GCP credentials private key.
+- `disableEntityManagement`  Optional. Default: false. When set to true, topics and subscriptions do not get created automatically.
+
+The above example uses secrets as plain strings. It is recommended to use a secret store for the secrets as described [here](../../concepts/secrets/README.md)
+
+## Apply the configuration
+
+### In Kubernetes
+
+To apply the Google Cloud pub/sub to Kubernetes, use the `kubectl` CLI:
+
+```bash
+kubectl apply -f messagebus.yaml
+```
+
+### Running locally
+
+The Dapr CLI will automatically create a directory named `components` in your current working directory. To use Cloud Pubsub, replace the contents of `messagebus.yaml` file with the contents of yaml above.