Creating a Multi-Tenant Event Bus with Cloud Pub/Sub

 Creating a Multi-Tenant Event Bus using Google Cloud Pub/Sub involves designing a system where multiple tenants (clients, customers, or applications) can send and receive messages through a shared event infrastructure, while maintaining data isolation, access control, and scalability.

Here’s a step-by-step guide to designing and implementing a multi-tenant event bus using Cloud Pub/Sub:

🔷 1. Understand the Multi-Tenant Requirements

Before implementation, clarify:

Isolation needs: Do tenants need hard or soft isolation?

Security: Who can publish/subscribe to which topics?

Message filtering: Will tenants receive only specific messages?

Scalability: How many tenants and message volume are expected?

Cost control: How will you track or limit usage per tenant?

🔷 2. Design Patterns

You have a few design options for tenant isolation:

Option A: Per-Tenant Topic and Subscription

Pros: Strong isolation.

Cons: Hard to scale with a large number of tenants.

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projects/your-project/topics/tenant-A-topic

projects/your-project/subscriptions/tenant-A-sub

Option B: Shared Topic, Filtered Subscriptions

Use message attributes to identify tenant.

Apply subscription filters to route only relevant messages.

Recommended for scalability.

Example:

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{

  "data": "Base64 encoded payload",

  "attributes": {

    "tenant_id": "tenant-123"

  }

}

Then apply a filter on subscription:

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attributes.tenant_id = "tenant-123"

🔷 3. Implement the Event Bus

Step 1: Create Shared Topics

Use the Google Cloud SDK:

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gcloud pubsub topics create shared-events

Step 2: Create Subscriptions with Filters

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gcloud pubsub subscriptions create tenant-123-sub \

  --topic=shared-events \

  --message-filter='attributes.tenant_id="tenant-123"'

Step 3: Publish Messages

Using SDKs or APIs, include tenant-specific attributes:

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from google.cloud import pubsub_v1

publisher = pubsub_v1.PublisherClient()

topic_path = publisher.topic_path("your-project", "shared-events")

future = publisher.publish(

    topic_path,

    b"Hello World",

    tenant_id="tenant-123"

)

🔷 4. Authentication and Access Control

Use IAM policies to:

Allow only certain service accounts to publish or subscribe.

Grant per-tenant permissions for reading from their subscription.

Example IAM binding:

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gcloud pubsub subscriptions add-iam-policy-binding tenant-123-sub \

  --member="serviceAccount:tenant-123@your-project.iam.gserviceaccount.com" \

  --role="roles/pubsub.subscriber"

🔷 5. Monitoring, Logging, and Billing

Use Cloud Monitoring and Cloud Logging to audit usage.

Enable Cloud Pub/Sub metrics to monitor message volume per tenant.

Use labels and Cloud Billing export to track tenant costs.

🔷 6. Advanced Tips

Dead Letter Topics: Configure for handling failed message deliveries.

Push Subscriptions: Use for near real-time processing.

Ordering: Enable message ordering if needed (per tenant key).

Retry Policies: Customize backoff strategies per subscription.

✅ Example Use Case Summary

Feature Configuration

Topic shared-events

Tenants Identified via attributes.tenant_id

Subscription One per tenant with filter

Access Control IAM roles per tenant subscription

Monitoring Cloud Monitoring with metrics per subscription

Scalability Easily supports hundreds or thousands of tenants

Learn Google Cloud Data Engineering Course

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