Cloud Pub/Sub provides reliable, many-to-many, asynchronous messaging between applications. Publisher applications can send messages to a topic, and other applications can subscribe to that topic to receive the messages.
- Follow the instructions in "Hello, World!" for Ruby on App Engine to set up your environment and project, and to understand how App Engine Ruby apps are structured.
- Write down and save your project ID, because you will need it to run the sample application described in this document.
Cloning the sample app
Copy the sample apps to your local machine, and navigate to the
git clone https://github.com/GoogleCloudPlatform/ruby-docs-samples cd ruby-docs-samples/appengine/pubsub
Creating a topic and subscription
Create a topic and subscription, which includes specifying the endpoint to which the Pub/Sub server should send requests:
gcloud pubsub topics create YOUR_TOPIC_NAME gcloud pubsub subscriptions create YOUR_SUBSCRIPTION_NAME \ --topic YOUR_TOPIC_NAME \ --push-endpoint \ https://YOUR_PROJECT_ID.appspot.com/pubsub/push?token=YOUR_TOKEN \ --ack-deadline 10
YOUR_TOKEN with a secret random token. The push endpoint uses this
to verify requests.
Setting environment variables
app.yaml file to set the environment variables for your project ID,
topic, and verification token:
env_variables: PUBSUB_TOPIC: <your-topic-name> # This token is used to verify that requests originate from your # application. It can be any sufficiently random string. PUBSUB_VERIFICATION_TOKEN: <your-token>
The sample app uses the Google Cloud Client Libraries.
The sample app uses the values you set in the
app.yaml file to configure
environment variables. The push request handler uses these values to confirm
that the request came from Pub/Sub and originated from a trusted source:
topic = pubsub.topic ENV["PUBSUB_TOPIC"] PUBSUB_VERIFICATION_TOKEN = ENV["PUBSUB_VERIFICATION_TOKEN"]
The sample app maintains a global list to store messages received by this instance:
# List of all messages received by this instance messages = 
This method receives pushed messages and adds them to the
post "/pubsub/push" do halt 400 if params[:token] != PUBSUB_VERIFICATION_TOKEN message = JSON.parse request.body.read payload = Base64.decode64 message["message"]["data"] messages.push payload end
This method interacts with the App Engine web app to publish new messages and display received messages:
get "/" do @messages = messages slim :index end post "/publish" do topic.publish params[:payload] redirect "/", 303 end
Running the sample locally
When running locally, you can use the Cloud SDK to provide authentication
to use Google Cloud APIs. Assuming you set up your environment as described in
Prerequisites, you have already run the
gcloud init command,
which provides this authentication.
Then set environment variables before starting your application:
export GOOGLE_CLOUD_PROJECT=[your-project-id] export PUBSUB_VERIFICATION_TOKEN=[your-verification-token] export PUBSUB_TOPIC=[your-topic] bundle exec ruby app.rb -p 8080
Simulating push notifications
The application can send messages locally, but it is not able to receive push
messages locally. You can, however, simulate a push message by making an HTTP
request to the local push notification endpoint. The sample includes the file
You can use
httpie to send an HTTP
curl -i --data @sample_message.json "localhost:8080/pubsub/push?token=[your-token]"
http POST ":8080/pubsub/push?token=[your-token]" < sample_message.json
HTTP/1.1 200 OK Content-Type: text/html;charset=utf-8 Content-Length: 13 X-Xss-Protection: 1; mode=block X-Content-Type-Options: nosniff X-Frame-Options: SAMEORIGIN Server: WEBrick/1.3.1 (Ruby/2.3.0/2015-12-25) Date: Wed, 20 Apr 2016 20:56:23 GMT Connection: Keep-Alive Hello, World!
After the request completes, you can refresh
localhost:8080 and see the
message in the list of received messages.
Running on App Engine
To deploy the demo app to App Engine by using the
tool, you run the following command from the directory where your
gcloud app deploy
You can now access the application at
You can use the form to submit messages, but there's no guarantee of which
instance of your application will receive the notification. You can send
multiple messages and refresh the page to see the received message.