Azure Event Hubs Docs

Geo-Disaster Recovery with Azure Event Hubs

Ensuring business continuity in the face of potential regional outages is critical for event-driven architectures. Azure Event Hubs provides robust mechanisms for implementing geo-disaster recovery (Geo-DR), allowing you to maintain your event ingestion and processing capabilities even when a primary region becomes unavailable.

How Geo-DR Works

Azure Event Hubs Geo-DR is implemented using a partnership between two Event Hubs namespaces: a primary namespace and a secondary namespace. These namespaces are located in different Azure regions. The Geo-DR feature automatically asynchronously replicates data from the primary namespace to the secondary namespace.

Key Components:

• Primary Namespace: The active Event Hubs namespace where your applications write events.
• Secondary Namespace: A passive Event Hubs namespace in a different region. It receives replicated data from the primary.
• Replication: Event Hubs asynchronously copies incoming events from the primary to the secondary namespace. This ensures that your data is available in a separate geographic location.
• Failover: In case of a disaster affecting the primary region, you can manually initiate a failover to the secondary namespace. This involves updating your applications to point to the secondary namespace.

Configuring Geo-DR

Configuring Geo-DR involves establishing a namespace pairing. This can be done through the Azure portal, Azure CLI, or Azure SDKs.

Steps in Azure Portal:

1. Navigate to your primary Event Hubs namespace.
2. In the left-hand menu, under "Settings", select "Geo-Disaster Recovery".
3. Click on "Pair with another namespace".
4. Select your desired secondary region and create a new Event Hubs namespace there, or select an existing one. Ensure it has the same configuration (partitions, retention, etc.) as the primary.
5. Initiate the pairing process. Replication will begin automatically once the pairing is established.

Failover Process

A failover is typically a manual process initiated by an operator when a disaster is detected. It involves redirecting your event producers and consumers to the secondary namespace.

Manual Failover Steps:

1. Stop Producers: Halt all event producers writing to the primary namespace.
2. Stop Consumers: Stop all event consumers reading from the primary namespace.
3. Initiate Failover: In the Azure portal (under Geo-Disaster Recovery for the primary namespace), select "Failover". This action makes the secondary namespace the primary.
4. Update Connection Strings: Update your application configurations to use the connection strings for the now-primary (formerly secondary) namespace.
5. Start Consumers: Restart your event consumers, now pointing to the new primary namespace.
6. Start Producers: Restart your event producers, also pointing to the new primary namespace.

Important Note: Data written to the primary namespace after the failover initiation but before producers are fully updated might not be replicated to the old primary namespace if it's being rebuilt or decommissioned.

Benefits of Geo-DR

• High Availability: Minimizes downtime during regional outages.
• Data Durability: Ensures your event data is available even if the primary region is lost.
• Business Continuity: Maintains critical event processing workflows.
• Simplified Management: Azure handles the asynchronous replication.

Considerations

• Asynchronous Replication: Geo-DR uses asynchronous replication, meaning there's a slight lag between an event arriving at the primary and being available at the secondary. This lag is typically minimal but can vary based on network conditions and load.
• Manual Failover: The failover process is manual. Automated failover solutions might require additional custom development or third-party tools.
• Cost: Running two Event Hubs namespaces incurs additional costs.
• Namespace Configuration: Ensure that the secondary namespace is configured identically to the primary (e.g., number of partitions) to avoid issues during failover.

Implementing Geo-Disaster Recovery is a vital step in building resilient and fault-tolerant event-driven solutions on Azure Event Hubs.