This Elixir app contains samples for working with Google Cloud Pub/Sub.

Installation

First, clone this repository:

git clone https://github.com/mcrumm/cloud_pubsub_samples.git
cd cloud_pubsub_samples

Next, install and compile the app:

mix do deps.get, compile

Now you're ready to setup your Google Cloud Project!

Getting Started

Create your Google Cloud Project

First, you need to create a Google Cloud Project and a Service Account with the proper permissions for managing Cloud Pub/Sub resources.

The Broadway project on HexDocs has a great tutorial for Google Cloud Project setup.

You can skip the steps about creating a topic and subscription, but be sure to create your Service Account, bind it with the proper permissions, and create a credentials file for authentication.

Configure Application Credentials

With credentials in hand, we can configure our environment to authenticate with Google. By default, this app will look for credentials in the GOOGLE_APPLICATION_CREDENTIALS System environment variable. Be sure to set the absolute path to your credentials file:

export GOOGLE_APPLICATION_CREDENTIALS="/path/to/my/credentials.json"

Create Resources

To use Google Cloud Pub/Sub, we need a topic and a subscription. Messages are published to topics and received by subscriptions.

Create a topic:

mix publisher.create test-topic
Created topic projects/test-project/topics/test-topic

And a subscription for the topic:

mix subscriber.create test-topic test-subscription
Created subscription projects/test-project/subscriptions/test-subscription

The Google Cloud Project is derived from the application credentials.

Start listening for messages

Start a subscriber for the subscription we just created:

mix subscriber.start test-subscription
Listening for messages on projects/test-project/subscriptions/test-subscription - Press Ctrl+C to exit

Publish messages

Open a new tab. Don't forget to export your application credentials.

Publish some messages to the topic:

mix publisher.publish test-topic
Published message 1
Published message 2
Published message 3
Published message 4
Published message 5
Published message 6
Published message 7
Published message 8
Published message 9
Published message 10

Switch back to the subscriber tab. You should see output similar to:

Received message from Cloud Pub/Sub:
  Message ID: 757042663206915
  Publish Time: 2019-09-22 19:16:25.183Z
  Attributes:
    nil

  The message data:
    "Message number 1"

Received message from Cloud Pub/Sub:
  ...

Commands

The following commands are made available as Mix tasks:

mix publisher.create           # Creates a Cloud Pub/Sub topic
mix publisher.delete           # Deletes a Cloud Pub/Sub topic
mix publisher.list             # Lists Cloud Pub/Sub topics for the current project
mix publisher.publish          # Publishes messages to a Cloud Pub/Sub topic
mix subscriber.create          # Creates a subscription for a Cloud Pub/Sub topic
mix subscriber.delete          # Deletes a subscription for a Cloud Pub/Sub topic
mix subscriber.list_in_project # Lists Cloud Pub/Sub subscriptions for the current project
mix subscriber.list_in_topic   # Lists Cloud Pub/Sub subscriptions for a topic
mix subscriber.start           # Listens for messages on a Cloud Pub/Sub subscription

To learn more about a given command and its arguments, run:

mix help <command>

Documentation

You can build the documentation for this project by running the docs command:

MIX_ENV=docs mix docs

The generated docs will be available at docs/index.html.