How to Create a Read Replica in Cloud SQL on GCP

To create a read replica in Cloud SQL, use the gcloud sql instances create command with the --master-instance-name flag pointing to the primary instance. This sets up a read-only copy that replicates data from the primary database automatically.

Syntax

Use the gcloud sql instances create command with these key parts:

• INSTANCE_NAME: The name for your new read replica.
• --master-instance-name=PRIMARY_INSTANCE: The name of the primary Cloud SQL instance to replicate.
• --region=REGION: The region where the replica will be created.

This command creates a read-only replica that syncs data from the primary instance.

bash

gcloud sql instances create INSTANCE_NAME \
  --master-instance-name=PRIMARY_INSTANCE \
  --region=REGION

Example

This example creates a read replica named my-read-replica in the us-central1 region, replicating from the primary instance my-primary-instance.

bash

gcloud sql instances create my-read-replica \
  --master-instance-name=my-primary-instance \
  --region=us-central1

Output

Created [https://sqladmin.googleapis.com/sql/v1beta4/projects/PROJECT_ID/instances/my-read-replica].

Common Pitfalls

Common mistakes when creating read replicas include:

• Not specifying the --master-instance-name, which causes the replica creation to fail.
• Choosing a region different from the primary without considering latency and cost.
• Trying to create a read replica for unsupported database versions or instance types.
• Not enabling binary logging on the primary instance, which is required for replication.

Always check that the primary instance has binary logging enabled and that the replica is compatible.

bash

## Wrong: Missing master-instance-name

gcloud sql instances create my-read-replica --region=us-central1

## Right: Include master-instance-name

gcloud sql instances create my-read-replica --master-instance-name=my-primary-instance --region=us-central1

Quick Reference

Tips for creating Cloud SQL read replicas:

• Use gcloud sql instances create with --master-instance-name.
• Ensure the primary instance has binary logging enabled.
• Choose the replica region wisely for performance and cost.
• Read replicas are read-only and help scale read traffic.

Key Takeaways

Use the gcloud command with --master-instance-name to create a read replica.

The primary instance must have binary logging enabled for replication.

Read replicas are read-only copies that improve read scalability.

Choose the replica region carefully to balance latency and cost.

Always verify compatibility between primary and replica instance types.