AWS CDK Elastic Load Balancing (V1)

Common errors

• ModuleNotFoundError: No module named 'aws_cdk.aws_elasticloadbalancingv2'

  cause Attempting to import v2 load balancer constructs (like ALB/NLB) after installing only the v1 Classic Load Balancer library.
  fix Install the correct CDK v2 library: `pip install aws-cdk.aws-elasticloadbalancingv2` or ensure you are using CDK v2.

• AttributeError: module 'aws_cdk.aws_elasticloadbalancing' has no attribute 'ApplicationLoadBalancer'

  cause Trying to instantiate an Application Load Balancer using the v1 Classic Load Balancer library.
  fix The `ApplicationLoadBalancer` construct is part of `aws_cdk.aws_elasticloadbalancingv2`. Import it from there: `from aws_cdk import aws_elasticloadbalancingv2 as elbv2`.

• TypeError: __init__() missing 1 required positional argument: 'scope'

  cause A CDK construct was instantiated without its required `scope` argument, which is typically the parent construct (e.g., `self` within a Stack).
  fix Ensure all CDK constructs are instantiated with `(self, "LogicalId", ...)` within a class extending `Construct` or `Stack`.

Warnings

• breaking AWS CDK v1 to v2 migration involves significant breaking changes across the entire CDK ecosystem. This `aws-cdk.aws-elasticloadbalancing` library is specific to CDK v1 and is not compatible with CDK v2 without a full migration of your CDK application.
  Fix: Migrate your CDK application to v2 and use the equivalent `aws-cdk.aws-elasticloadbalancingv2` or `aws-cdk.aws-ec2` constructs where applicable, following the official AWS CDK migration guide.
• gotcha This library specifically manages *Classic Load Balancers (ELBv1)*. Do not confuse it with Application Load Balancers (ALB) or Network Load Balancers (NLB), which are managed by the `aws-cdk.aws-elasticloadbalancingv2` library.
  Fix: For ALB or NLB, ensure you install and import from `aws-cdk.aws-elasticloadbalancingv2`. For Classic Load Balancers, continue using this library.
• deprecated AWS Classic Load Balancers themselves are considered a legacy service by AWS, with Application and Network Load Balancers being the recommended modern alternatives. New deployments should generally prefer ELBv2 constructs.
  Fix: Consider using `aws-cdk.aws-elasticloadbalancingv2` for new load balancer deployments, leveraging Application or Network Load Balancers for improved features and performance.

Install

• pip install aws-cdk.aws-elasticloadbalancing aws-cdk.core aws-cdk.aws-ec2 constructs Install core CDK v1, ELB, EC2 and Constructs libraries

Imports

• CfnLoadBalancer
  wrong:

  from aws_cdk.aws_elasticloadbalancingv2 import ApplicationLoadBalancer

  correct:

  from aws_cdk import aws_elasticloadbalancing as elb

  This library is for Classic Load Balancers (ELBv1). For Application or Network Load Balancers, use `aws_cdk.aws_elasticloadbalancingv2`.

Quickstart

This quickstart deploys a basic AWS Classic Load Balancer (ELBv1) within a new VPC using CDK v1. It creates an internet-facing load balancer with an HTTP listener on port 80, routing traffic to instances (not shown) on port 80. Ensure `CDK_DEFAULT_ACCOUNT` and `CDK_DEFAULT_REGION` environment variables are set.

import os
from aws_cdk import (
    App, Stack, Environment,
    aws_ec2 as ec2,
    aws_elasticloadbalancing as elb,
    CfnOutput
)
from constructs import Construct

class ElbV1Stack(Stack):
    def __init__(self, scope: Construct, id: str, **kwargs) -> None:
        super().__init__(scope, id, **kwargs)

        # Create a VPC
        vpc = ec2.Vpc(self, "MyVpc",
            max_azs=2,
            cidr="10.10.0.0/16",
            subnet_configuration=[
                ec2.SubnetConfiguration(
                    name="Public",
                    subnet_type=ec2.SubnetType.PUBLIC,
                    cidr_mask=24
                ),
                ec2.SubnetConfiguration(
                    name="Private",
                    subnet_type=ec2.SubnetType.PRIVATE_ISOLATED,
                    cidr_mask=24
                )
            ]
        )

        # Select public subnets for the Classic Load Balancer
        public_subnets = vpc.select_subnets(subnet_type=ec2.SubnetType.PUBLIC)

        # Create a Classic Load Balancer
        clb = elb.CfnLoadBalancer(self, "MyClassicLoadBalancer",
            listeners=[
                elb.CfnLoadBalancer.ListenersProperty(
                    instance_port="80",
                    instance_protocol="HTTP",
                    load_balancer_port="80",
                    protocol="HTTP"
                )
            ],
            scheme="internet-facing",
            subnets=[s.subnet_id for s in public_subnets.subnets]
            # For production, consider adding security_groups and health_check.
            # The CLB will create a default security group if none is provided.
        )

        CfnOutput(self, "LoadBalancerDNS", value=clb.get_att("DNSName").to_string())

app = App()
ElbV1Stack(app, "ElbV1ExampleStack",
    env=Environment(
        account=os.environ.get("CDK_DEFAULT_ACCOUNT"),
        region=os.environ.get("CDK_DEFAULT_REGION")
    )
)
app.synth()