Visit https://serverless-push.demo.hasura.app/ for a live demo.

• Google Cloud account with billing enabled
• Firebase Cloud Messaging (FCM) account
• Hasura GraphQL Engine (HGE) installation

Goto HGE console and create the following table:

Table name: message

Columns:

id            UUID        default: gen_random_uuid()
timestamp     Timestamp   default: now()
title         Text
body          Text        nullable
device_token  Text

Primary key: id

• Create a new project or use an existing project on Firebase Console.
• Note down the Google Cloud project name - also called PROJECT_ID.
• Open the Cloud Messaging tab of the Firebase console Settings pane and scroll to the Web configuration section.
• In the Web Push certificates tab, click Generate Key Pair. The console displays a notice that the key pair was generated, and displays the public key string and date added.
• Copy the Key Pair (we'll call it FCM_PUBLIC_KEY).
• Note down the Sender ID from top of this page (SENDER_ID);
• Also note down the Server Key (SERVER_KEY).

We'll configure HGE to send an event to a webhook trigger whenever an insert happens on the message table. The data inserted to this table contains the notification text and a unique device token. The webhook receives this data and makes an API call to Firebase to send a push notification to that unique device.

We'll deploy this webhook as a Google Cloud Function.

• Execute the command to deploy the function:

  cd cloudfunction
  gcloud beta functions deploy push-notification \
         --runtime nodejs8 --trigger-http \
         --set-env-vars="FCM_SERVER_KEY=<SERVER_KEY>"
  
• Copy URL from the output (TRIGGER_URL)

  httpsTrigger:
    url: https://us-central1-hasura-test.cloudfunctions.net/push-notification

Goto HGE console and then to the "Events" tab. Here we can add triggers which will be executed on insert/update/delete actions on tables configured.

Add a new trigger with details as follows:

Trigger name:  message_event
Schema/Table:  public/message
Operations:    Insert
Webhook URL:   <TRIGGER_URL>

Use the TRIGGER_URL from the cloudfunction deployment.

• Edit index.html, add PROJECT_ID and SENDER_ID.
• Edit index.js, add FCM_PUBLIC_KEY and Hasura GraphQL Engine url (HGE_URL)

Run any HTTP server locally and visit the URL on browser.

http-server

Note: If you're deploying to any server other than localhost, service workers will only work if the scheme is HTTPS.