Prioritizing traffic with weighted target groups for A/B testing

Question

Pulumi · Accepted Answer

In order to prioritize traffic with weighted target groups for A/B testing using AWS, you will need to use an Application Load Balancer (ALB) that routes requests to multiple target groups with different weights. This setup enables you to control the percentage of traffic that is sent to each target group, which can be useful for A/B testing or blue/green deployments.

To define this infrastructure as code using Pulumi, you'll need to declare an ALB, at least two target groups, and configure the listener rules to distribute incoming traffic according to your desired weights. Below I'll provide a Pulumi program written in TypeScript that creates such a setup. We'll use the `aws.alb.TargetGroup` for defining the target groups and `aws.alb.ListenerRule` to apply the weighted routing rules.

The following code will guide you through setting up the infrastructure for managing A/B testing traffic flow:

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

// Define an Application Load Balancer (ALB)
const alb = new aws.lb.LoadBalancer("app-lb", {
    internal: false,
    loadBalancerType: "application",
    securityGroups: [/* Add your security group IDs here */],
    subnets: [/* Add your subnet IDs here */],
});

// Define the two target groups for A/B testing
const targetGroupA = new aws.lb.TargetGroup("target-group-a", {
    port: 80,
    protocol: "HTTP",
    vpcId: /* Provide your VPC ID here */,
});

const targetGroupB = new aws.lb.TargetGroup("target-group-b", {
    port: 80,
    protocol: "HTTP",
    vpcId: /* Provide your VPC ID here */,
});

// Define a listener for the ALB
const listener = new aws.lb.Listener("listener", {
    loadBalancerArn: alb.arn,
    port: 80,
    protocol: "HTTP",
});

// Define listener rules to route traffic based on weights
const listenerRuleA = new aws.lb.ListenerRule("listener-rule-a", {
    actions: [
        {
            type: "forward",
            targetGroupArn: targetGroupA.arn,
            // Define the weight for A target group, e.g., 20% of the traffic
            forwardWeight: 20,
        },
        {
            type: "forward",
            targetGroupArn: targetGroupB.arn,
            // Automatically set the weight for B to the remainder, e.g., 80%
        },
    ],
    listenerArn: listener.arn,
    conditions: [
        {
            pathPattern: {
                values: ["/some-path/*"], // Define the path pattern (modify according to your needs)
            },
        },
    ],
    priority: 10, // Set the rule priority
});

// Export the DNS name of the load balancer for easy access
export const albDnsName = alb.dnsName;
```

Here is what the above code does:

1. **Load Balancer (ALB)**: We create an ALB that will handle incoming requests and distribute them to target groups based on rules defined.
   
2. **Target Groups**: We define two separate target groups (`targetGroupA` and `targetGroupB`) that will handle the requests forwarded by the ALB. Each target group should include your ECS services, EC2 instances, or Lambda functions that serve the two versions of your application.

3. **Listener**: An ALB listener is created, which listens for HTTP traffic on the specified port (in this case, port 80).

4. **Listener Rules**: We use the `ListenerRule` resource to define how the ALB should route requests. Here, we specify that 20% of the traffic should be sent to `targetGroupA` and the rest to `targetGroupB`. You will adjust the weights according to your A/B testing requirements.

5. **Exports**: Finally, we export the DNS name of the ALB, which is how users will access your services.

Remember to replace the placeholders with your actual subnet IDs, security group IDs, and VPC ID. Adjust the routing conditions and weights to fit your A/B testing goals.

After deploying this Pulumi program, traffic hitting the load balancer will be distributed between `targetGroupA` and `targetGroupB` based on the weights specified in the listener rule, allowing you to carry out A/B testing with the desired amount of traffic allocated to each version of your app.