How do I attach an instance to an application target group?

❓ General Issue

The Question

Hi, I’d like to create an application load balancer that has a listener pointing to a target group with a single instance target.

Not sure if I took the right approach at the first place (cannot find any relevant doc), but now I just can’t move on and I’m afraid I discovered a bug in CDK.

Environment

• CDK CLI Version: 1.18.0 (build bc924bc)
• Module Version: ?
• OS: Kubuntu 18.04
• Language: Python

Other information

This is my code:

from aws_cdk import (
    core,
    aws_ec2,
    aws_elasticloadbalancingv2,
)

class WebsiteStack(core.Stack):

    def __init__(self, scope: core.Construct, id: str, **kwargs) -> None:
        super().__init__(scope, id, **kwargs)

        self.vpc = aws_ec2.Vpc.from_lookup(self, 'default_vpc', is_default=True)

        self.sg_ssh = aws_ec2.SecurityGroup(
            self,
            'ssh',
            vpc=self.vpc,
            description="Allow SSH from anywhere",
            security_group_name="SSH from anywhere"
        )
        self.sg_ssh.add_ingress_rule(aws_ec2.Peer.any_ipv4(), aws_ec2.Port.tcp(22))

        ami = aws_ec2.LookupMachineImage(
            name="ubuntu/images/hvm-ssd/ubuntu-bionic-18.04-amd64-server-*",
            owners=["099720109477"],
        )

        ec2 = aws_ec2.Instance(
            self,
            'website',
            instance_type=aws_ec2.InstanceType('t3a.micro'),
            machine_image=ami,
            vpc=self.vpc,
            security_group=self.sg_ssh,
        )

        tg = aws_elasticloadbalancingv2.ApplicationTargetGroup(
            self,
            'website-target-group',
            protocol=aws_elasticloadbalancingv2.ApplicationProtocol.HTTP,
            port=80,
            vpc=self.vpc,
            # target_type=aws_elasticloadbalancingv2.TargetType.INSTANCE,
            # targets=[ec2],  # FIXME
        )
        tg.add_target(ec2)  # FIXME

Running either cdk diff or cdk deploy with one of the “FIXME” - commented line uncommented leads to the following error:

$ cdk diff
jsii.errors.JavaScriptError:
  TypeError: target.attachToApplicationTargetGroup is not a function
      at ApplicationTargetGroup.addTarget (/tmp/jsii-kernel-Tq3fWv/node_modules/@aws-cdk/aws-elasticloadbalancingv2/lib/alb/application-target-group.js:52:35)
      at _wrapSandboxCode (/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7582:51)
      at Kernel._wrapSandboxCode (/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_embedded/jsii/jsii-runtime.js:8205:19)
      at ret._ensureSync (/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7582:25)
      at Kernel._ensureSync (/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_embedded/jsii/jsii-runtime.js:8178:20)
      at Kernel.invoke (/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7581:26)
      at KernelHost.processRequest (/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7293:28)
      at KernelHost.run (/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7233:14)
      at Immediate.setImmediate [as _onImmediate] (/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7236:37)
      at runCallback (timers.js:705:18)
      at tryOnImmediate (timers.js:676:5)
      at processImmediate (timers.js:658:5)

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "app.py", line 11, in <module>
    'account': '483******425',
  File "/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_runtime.py", line 66, in __call__
    inst = super().__call__(*args, **kwargs)
  File "/home/my/cdktest/website/website_stack.py", line 84, in __init__
    tg.add_target(ec2)  # FIXME
  File "/home/my/cdktest/.env/lib/python3.6/site-packages/aws_cdk/aws_elasticloadbalancingv2/__init__.py", line 8168, in add_target
    return jsii.invoke(self, "addTarget", [*targets])
  File "/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_kernel/__init__.py", line 107, in wrapped
    return _recursize_dereference(kernel, fn(kernel, *args, **kwargs))
  File "/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_kernel/__init__.py", line 282, in invoke
    args=_make_reference_for_native(self, args),
  File "/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_kernel/providers/process.py", line 348, in invoke
    return self._process.send(request, InvokeResponse)
  File "/home/my/cdktest/.env/lib/python3.6/site-packages/jsii/_kernel/providers/process.py", line 318, in send
    raise JSIIError(resp.error) from JavaScriptError(resp.stack)
jsii.errors.JSIIError: target.attachToApplicationTargetGroup is not a function
Subprocess exited with error 1

[rahejaps]

@porn, Thank you. I was able get some help from the gitter forum. I modified the listener code as follows.

from aws_cdk import aws_elasticloadbalancingv2_targets as targets

     listener.add_targets(
           'ec2_instance', 
           port=3130, 
           targets=[targets.InstanceIdTarget(
               instance_id=ec2a,
               port=3130
               ),
            targets.InstanceIdTarget(
               instance_id=ec2b,
               port=3130)]
         )

[porn]

Hi @rahejaps,

I don’t have any code that is being used, but by the time I raised this bug, i was experimenting with various infra-as-code toolkits. You can check this one out, maybe it’ll be helpful: https://gitlab.com/ikar/infrastructure-as-code/-/blob/master/cdk-py/website/website_stack.py