Setting up read replicas for database scaling.

Question

Pulumi · Accepted Answer

Creating read replicas is an effective way to scale out the ability to handle read queries on a database system. When you create a read replica, you are effectively setting up a copy of your primary database that will handle read operations. This can help offset the load on the primary database, potentially improving performance and availability.

In this tutorial, we will use Pulumi with TypeScript to set up read replicas in AWS using the `aws.rds.Instance` resource. AWS RDS (Relational Database Service) supports read replicas for MySQL, PostgreSQL, MariaDB, Oracle, and SQL Server. Here we will look at an example for MySQL, but the process is similar for other engines.

To create read replicas using Pulumi, you will typically do the following:

1. Set up a primary RDS database instance.
2. Create one or more read replica instances and configure them to replicate from the primary instance.

Here is a program that sets up a primary MySQL RDS instance and a single read replica. Before running this program, make sure you have AWS credentials configured for your Pulumi environment.

```typescript
import * as pulumi from "@pulumi/pulumi";
import * as aws from "@pulumi/aws";

// Create a primary RDS instance
const primaryDb = new aws.rds.Instance("primary-db", {
    instanceClass: "db.t3.micro",
    allocatedStorage: 20, // GB
    engine: "mysql",
    engineVersion: "8.0.20",
    username: "admin",
    password: "somesecurepassword", // Replace with a more secure password
    dbSubnetGroupName: "my-db-subnet-group", // Ensure this subnet group is created
    vpcSecurityGroupIds: ["sg-xxxxxxxx"], // Replace with your VPC security group ID
    skipFinalSnapshot: true,
});

// Create a read replica
const readReplica = new aws.rds.Instance("read-replica", {
    instanceClass: "db.t3.micro",
    allocatedStorage: 20, // Should be the same or larger than the primary
    engine: "mysql",
    engineVersion: "8.0.20",
    username: "admin",
    password: "somesecurepassword", // Keep the credentials same as primary (or use Secrets Manager)
    dbSubnetGroupName: "my-db-subnet-group", // Ensure this subnet group is created
    vpcSecurityGroupIds: ["sg-xxxxxxxx"], // Replace with your VPC security group ID
    skipFinalSnapshot: true,
    replicateSourceDb: primaryDb.id, // This links the replica to the primary instance
});

// Export the address and port of the read replica
export const replicaAddress = readReplica.address;
export const replicaPort = readReplica.port;
```

In this program, the `aws.rds.Instance` resource creates an RDS instance. The properties you provide determine the size, engine, and other configurations of the instance. For the read replica, the key property is `replicateSourceDb`, which establishes its link to the primary RDS instance, signifying that it should act as a replica of the referenced primary.

Keep in mind that there are other configurations and best practices that you should follow, such as setting up backups, monitoring, and using AWS Secrets Manager for password storage. Also, managing the allocation of resources and overall database security should be carefully considered.

This is a simplified example for illustrative purposes. You will need to adjust your configuration to fit your needs, such as the instance class for production workloads, allocated storage, and other engine-specific settings.

If your primary database is very write-heavy or if you need to distribute your read replicas across different geographical regions for latency or compliance reasons, AWS RDS supports these configurations as well.

Finally, you should be aware of the costs associated with running multiple RDS instances. AWS charges for read replicas in addition to the primary instance, so make sure you account for these costs in your budget.