GCP Pub/Sub

Connect Webhook Relay to Google Cloud Pub/Sub to receive messages from subscriptions (input) or publish webhook data to topics (output).

Prerequisites

• A GCP service connection with a service account that has Pub/Sub permissions
• A Pub/Sub topic and subscription in your GCP project

GCP Roles

For Pub/Sub Input (subscribe):

• roles/pubsub.subscriber — the subscription must already exist in your project

For Pub/Sub Output (publish):

• roles/pubsub.publisher

Pub/Sub Input — Receive Messages from a Subscription

Pub/Sub inputs subscribe to an existing subscription and relay messages into your Webhook Relay bucket. Messages are auto-acknowledged after successful relay. Message data and attributes are wrapped in a JSON envelope.

Configuration

The subscription must be pre-created in your GCP project before adding it as an input. Webhook Relay does not create subscriptions automatically.

Pub/Sub Output — Publish Webhooks to a Topic

Pub/Sub outputs publish incoming webhook data as messages to your Pub/Sub topic. The topic must already exist in your project. You can find them in your "Pub/Sub" section in the GCP console:

Configuration

Example: Bridge AWS SQS to GCP Pub/Sub

Route messages from an AWS SQS queue into a GCP Pub/Sub topic. This is ideal for migrating workloads across cloud providers or running multi-cloud architectures:

1. Create an AWS service connection with SQS read permissions
2. Create a GCP service connection with Pub/Sub publisher permissions
3. Create a bucket in Webhook Relay
4. Add an AWS SQS input on the bucket
5. Add a GCP Pub/Sub output on the bucket

Messages polled from SQS are automatically published to your Pub/Sub topic.

Transform Between Formats

Attach a Function to adapt the message format. For example, convert an SQS message into a structured Pub/Sub payload:

const sqsMessage = JSON.parse(r.body)

// Restructure for Pub/Sub consumers
const pubsubPayload = {
    source: "aws-sqs",
    original_message_id: sqsMessage.MessageId,
    data: sqsMessage.Body,
    bridged_at: new Date().toISOString()
}

r.setBody(JSON.stringify(pubsubPayload))

See the JSON encoding guide for more transformation examples.

Example: Pub/Sub to Any HTTPS Endpoint

Deliver Pub/Sub messages as webhooks to any API that accepts HTTPS requests. This works well for services without native GCP integration:

1. Create a GCP service connection
2. Create a bucket with a Pub/Sub input
3. Add a public destination (any HTTPS URL)

Use a Function to add authentication or transform the payload before delivery:

const message = JSON.parse(r.body)

// Forward only the message data, add auth header
r.setBody(message.data)
r.setHeader("Authorization", "Bearer " + cfg.get("API_TOKEN"))
r.setHeader("Content-Type", "application/json")

See configuration variables for how to securely store API tokens in functions.

Example: Pub/Sub to Localhost for Development

Receive Pub/Sub messages on your local machine during development — no need to deploy to GCP:

1. Create a GCP service connection
2. Create a bucket with a Pub/Sub input
3. Add an internal destination pointing to http://localhost:3000/webhook
4. Run the Webhook Relay agent locally

Messages from your Pub/Sub subscription are forwarded to your local server in real time.

Example: AWS S3 Notifications to GCP Pub/Sub

Publish S3 object notifications to a Pub/Sub topic. Useful when your processing pipeline runs on GCP but data arrives in S3:

1. Create an AWS service connection with S3 read permissions
2. Create a GCP service connection with Pub/Sub publisher permissions
3. Create a bucket with an AWS S3 input and a GCP Pub/Sub output

Optionally add a function to filter or transform the S3 event notification before publishing to Pub/Sub.