Amazon Elastic Load Balancing V2 Construct Library

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The @aws-cdk/aws-elasticloadbalancingv2 package provides constructs for configuring application and network load balancers.

For more information, see the AWS documentation for Application Load Balancers and Network Load Balancers.

Defining an Application Load Balancer

You define an application load balancer by creating an instance of ApplicationLoadBalancer, adding a Listener to the load balancer and adding Targets to the Listener:

import ec2 = require('@aws-cdk/aws-ec2');
import elbv2 = require('@aws-cdk/aws-elasticloadbalancingv2');
import autoscaling = require('@aws-cdk/aws-autoscaling');

// ...

const vpc = new ec2.Vpc(...);

// Create the load balancer in a VPC. 'internetFacing' is 'false'
// by default, which creates an internal load balancer.
const lb = new elbv2.ApplicationLoadBalancer(this, 'LB', {
    vpc,
    internetFacing: true
});

// Add a listener and open up the load balancer's security group
// to the world. 'open' is the default, set this to 'false'
// and use `listener.connections` if you want to be selective
// about who can access the listener.
const listener = lb.addListener('Listener', {
    port: 80,
    open: true,
});

// Create an AutoScaling group and add it as a load balancing
// target to the listener.
const asg = new autoscaling.AutoScalingGroup(...);
listener.addTargets('ApplicationFleet', {
    port: 8080,
    targets: [asg]
});

The security groups of the load balancer and the target are automatically updated to allow the network traffic.

Use the addFixedResponse() method to add fixed response rules on the listener:

listener.addFixedResponse('Fixed', {
    pathPattern: '/ok',
    contentType: elbv2.ContentType.TEXT_PLAIN,
    messageBody: 'OK',
    statusCode: '200'
});

Conditions

It's possible to route traffic to targets based on conditions in the incoming HTTP request. Path- and host-based conditions are supported. For example, the following will route requests to the indicated AutoScalingGroup only if the requested host in the request is example.com:

listener.addTargets('Example.Com Fleet', {
    priority: 10,
    hostHeader: 'example.com',
    port: 8080,
    targets: [asg]
});

priority is a required field when you add targets with conditions. The lowest number wins.

Every listener must have at least one target without conditions.

Defining a Network Load Balancer

Network Load Balancers are defined in a similar way to Application Load Balancers:

import ec2 = require('@aws-cdk/aws-ec2');
import elbv2 = require('@aws-cdk/aws-elasticloadbalancingv2');
import autoscaling = require('@aws-cdk/aws-autoscaling');

// Create the load balancer in a VPC. 'internetFacing' is 'false'
// by default, which creates an internal load balancer.
const lb = new elbv2.NetworkLoadBalancer(this, 'LB', {
    vpc,
    internetFacing: true
});

// Add a listener on a particular port.
const listener = lb.addListener('Listener', {
    port: 443,
});

// Add targets on a particular port.
listener.addTargets('AppFleet', {
    port: 443,
    targets: [asg]
});

One thing to keep in mind is that network load balancers do not have security groups, and no automatic security group configuration is done for you. You will have to configure the security groups of the target yourself to allow traffic by clients and/or load balancer instances, depending on your target types. See Target Groups for your Network Load Balancers and Register targets with your Target Group for more information.

Targets and Target Groups

Application and Network Load Balancers organize load balancing targets in Target Groups. If you add your balancing targets (such as AutoScalingGroups, ECS services or individual instances) to your listener directly, the appropriate TargetGroup will be automatically created for you.

If you need more control over the Target Groups created, create an instance of ApplicationTargetGroup or NetworkTargetGroup, add the members you desire, and add it to the listener by calling addTargetGroups instead of addTargets.

addTargets() will always return the Target Group it just created for you:

const group = listener.addTargets('AppFleet', {
    port: 443,
    targets: [asg1],
});

group.addTarget(asg2);

Using Lambda Targets

To use a Lambda Function as a target, use the integration class in the @aws-cdk/aws-elasticloadbalancingv2-targets package:

import lambda = require('@aws-cdk/aws-lambda');
import elbv2 = require('@aws-cdk/aws-elasticloadbalancingv2');
import targets = require('@aws-cdk/aws-elasticloadbalancingv2-targets');

const lambdaFunction = new lambda.Function(...);
const lb = new elbv2.ApplicationLoadBalancer(...);

const listener = lb.addListener('Listener', { port: 80 });
listener.addTargets('Targets', {
    targets: [new targets.LambdaTarget(lambdaFunction)]
});

Only a single Lambda function can be added to a single listener rule.

Configuring Health Checks

Health checks are configured upon creation of a target group:

listener.addTargets('AppFleet', {
    port: 8080,
    targets: [asg],
    healthCheck: {
        path: '/ping',
        interval: cdk.Duration.minutes(1),
    }
});

The health check can also be configured after creation by calling configureHealthCheck() on the created object.

No attempts are made to configure security groups for the port you're configuring a health check for, but if the health check is on the same port you're routing traffic to, the security group already allows the traffic. If not, you will have to configure the security groups appropriately:

listener.addTargets('AppFleet', {
    port: 8080,
    targets: [asg],
    healthCheck: {
        port: 8088,
    }
});

listener.connections.allowFrom(lb, ec2.Port.tcp(8088));

Using a Load Balancer from a different Stack

If you want to put your Load Balancer and the Targets it is load balancing to in different stacks, you may not be able to use the convenience methods loadBalancer.addListener() and listener.addTargets().

The reason is that these methods will create resources in the same Stack as the object they're called on, which may lead to cyclic references between stacks. Instead, you will have to create an ApplicationListener in the target stack, or an empty TargetGroup in the load balancer stack that you attach your service to.

For an example of the alternatives while load balancing to an ECS service, see the ecs/cross-stack-load-balancer example.

Protocol for Load Balancer Targets

Constructs that want to be a load balancer target should implement IApplicationLoadBalancerTarget and/or INetworkLoadBalancerTarget, and provide an implementation for the function attachToXxxTargetGroup(), which can call functions on the load balancer and should return metadata about the load balancing target:

public attachToApplicationTargetGroup(targetGroup: ApplicationTargetGroup): LoadBalancerTargetProps {
    targetGroup.registerConnectable(...);
    return {
        targetType: TargetType.Instance | TargetType.Ip
        targetJson: { id: ..., port: ... },
    };
}

targetType should be one of Instance or Ip. If the target can be directly added to the target group, targetJson should contain the id of the target (either instance ID or IP address depending on the type) and optionally a port or availabilityZone override.

Application load balancer targets can call registerConnectable() on the target group to register themselves for addition to the load balancer's security group rules.

If your load balancer target requires that the TargetGroup has been associated with a LoadBalancer before registration can happen (such as is the case for ECS Services for example), take a resource dependency on targetGroup.loadBalancerDependency() as follows:

// Make sure that the listener has been created, and so the TargetGroup
// has been associated with the LoadBalancer, before 'resource' is created.
resourced.addDependency(targetGroup.loadBalancerDependency());