Registering a Fargate service ELB target with correct port using CDK? - aws-fargate

Question

I'm trying to add a fargate service as an Application Load Balancer target but it keeps getting the wrong container port. The task definition has two containers: an app on port 8080 and an nginx reverse proxy on port 443. When I try to wire these together via the CDK the target registration always gets port 8080. I can't seem to find a method or set of props that lets me tell the CDK which container's port to use. Or maybe I am and it's ignoring it? What am I missing?
Here's a trimmed down example construct:
export class CdkFargateElbStack extends cdk.Stack {
constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
super(scope, id, props);
const vpc = new ec2.Vpc(this, 'Vpc', { maxAzs: 2 });
const cluster = new ecs.Cluster(this, 'Cluster', {
vpc: vpc,
});
const taskDef = new FargateTaskDefinition(this, 'TaskDefinition');
const appContainer = new ContainerDefinition(this, 'AppContainer', {
image: ContainerImage.fromRegistry(APP_IMAGE),
taskDefinition: taskDef,
});
appContainer.addPortMappings({
hostPort: 8080,
containerPort: 8080
});
const proxyContainer = new ContainerDefinition(this, 'ProxyContainer', {
image: ContainerImage.fromRegistry(PROXY_IMAGE),
taskDefinition: taskDef,
})
proxyContainer.addPortMappings({
hostPort: 443,
containerPort: 443,
});
const service = new FargateService(this, 'Service', {
cluster: cluster,
taskDefinition: taskDef,
assignPublicIp: true,
desiredCount: 1,
vpcSubnets: vpc.selectSubnets({
subnetType: ec2.SubnetType.PUBLIC,
}),
});
const alb = new elb.ApplicationLoadBalancer(this, 'LoadBalancer', {
vpc: vpc,
internetFacing: true,
ipAddressType: elb.IpAddressType.IPV4,
vpcSubnets: vpc.selectSubnets({
subnetType: ec2.SubnetType.PUBLIC,
})
});
const tg = new ApplicationTargetGroup(this, 'TargetGroup', {
protocol: elb.ApplicationProtocol.HTTPS,
port: 443,
vpc: vpc,
targetType: elb.TargetType.IP,
targets: [ service ],
});
const listener = alb.addListener('Listener', {
protocol: elb.ApplicationProtocol.HTTPS,
port: 443,
certificateArns: [ CERTIFICATE_ARN ],
defaultTargetGroups: [tg]
});
const rule = new ApplicationListenerRule(this, 'rule', {
listener,
priority: 1,
pathPattern: '*',
targetGroups: [ tg ],
});
}
}
Here's the resulting target registrations. I need the port here to be 443.

Answer 1

According to the documentation from ecs.FargateService.loadBalancerTarget, the container which will be selected as the ALB target is the first essential container from the task definition.
To use other containers create a service reference like this:
const sTarget = service.loadBalancerTarget({
containerName: 'MyContainer',
containerPort: 1234
}));
Then add sTarget to the targetGroup services.