How do I configure an AWS Load Balancer Listener Rule?

In this guide, we’ll configure an AWS Load Balancer listener rule to help you manage traffic routing to your applications. Listener rules for an AWS load balancer allow you to direct traffic based on certain conditions, like path patterns or host headers.

The example will cover creating an AWS Load Balancer, a listener, and a listener rule. This setup is key for directing traffic to the appropriate target groups based on different conditions.

Here’s how to do it:

Create an AWS Load Balancer: This will be the entry point for all incoming traffic.
Define a Listener: This listens for connection requests from clients.
Add a Listener Rule: This rule will direct traffic to the appropriate target group based on specified conditions.

Below is the code block with comments explaining each resource.

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

// Create a VPC
const main = new aws.ec2.Vpc("main", {cidrBlock: "10.0.0.0/16"});
// Create an internet gateway for the VPC
const mainInternetGateway = new aws.ec2.InternetGateway("main", {vpcId: main.id});
// Create a subnet for the VPC
const mainSubnet = new aws.ec2.Subnet("main", {
    vpcId: main.id,
    cidrBlock: "10.0.1.0/24",
});
// Create a security group to allow HTTP traffic
const lbSg = new aws.ec2.SecurityGroup("lb_sg", {
    vpcId: main.id,
    ingress: [{
        fromPort: 80,
        toPort: 80,
        protocol: "tcp",
        cidrBlocks: ["0.0.0.0/0"],
    }],
    egress: [{
        fromPort: 0,
        toPort: 0,
        protocol: "-1",
        cidrBlocks: ["0.0.0.0/0"],
    }],
});
// Create a load balancer
const mainLoadBalancer = new aws.lb.LoadBalancer("main", {
    name: "example-lb",
    internal: false,
    loadBalancerType: "application",
    securityGroups: [lbSg.id],
    subnets: [mainSubnet.id],
});
// Create a target group
const mainTargetGroup = new aws.lb.TargetGroup("main", {
    name: "example-tg",
    port: 80,
    protocol: "HTTP",
    vpcId: main.id,
});
// Create a listener on the load balancer
const mainListener = new aws.lb.Listener("main", {
    loadBalancerArn: mainLoadBalancer.arn,
    port: 80,
    protocol: "HTTP",
    defaultActions: [{
        type: "forward",
        targetGroupArn: mainTargetGroup.arn,
    }],
});
// Create a listener rule
const mainListenerRule = new aws.lb.ListenerRule("main", {
    listenerArn: mainListener.arn,
    priority: 99,
    actions: [{
        type: "forward",
        targetGroupArn: mainTargetGroup.arn,
    }],
    conditions: [{
        pathPattern: {
            values: ["/path/*"],
        },
    }],
});
export const lbDnsName = mainLoadBalancer.dnsName;
export const listenerArn = mainListener.arn;
export const listenerRuleId = mainListenerRule.id;

Key Points:

AWS Load Balancer: Handles incoming traffic.
Listener: Listens for incoming connection requests.
Listener Rule: Directs traffic based on specific conditions like URL path patterns.

Summary:

In this guide, we configured an AWS Load Balancer listener rule to control how incoming traffic gets routed to different target groups, enhancing control over your application traffic flow.

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