Using an existing load balancer with ApplicationLoadBalancedEc2Service

[vishal-scg]

I am using the below code to use an existing ALB but getting some errors .

`import aws_cdk as cdk
from aws_cdk import aws_ecs as ecs
from aws_cdk import aws_ec2 as ec2
from aws_cdk import aws_ecs_patterns as ecs_patterns
from aws_cdk import aws_autoscaling as autoscaling
from aws_cdk import aws_elasticloadbalancingv2 as elb

class EcsCdkStack(cdk.Stack):

def __init__(self, scope: cdk.App, construct_id: str, **kwargs) -> None:
    
    super().__init__(scope, construct_id, **kwargs)
    
    # Create task_definition
    task_definition = ecs.Ec2TaskDefinition(self, "llmcdkdef")
    container = task_definition.add_container(id="llmcontainer",
        image=ecs.ContainerImage.from_registry(""),
        environment= {
            "BIND": "0.0.0.0:8000",
            "LOG_LEVEL" : "DEBUG",
            "MODEL_NAME" : "distilbert-base-uncased",
            "THREADS" : "1" ,
            "TIMEOUT" : "60",
            "WORKERS" : "4"   
        },
        logging=ecs.LogDrivers.aws_logs(stream_prefix="llmcdk"),
        memory_reservation_mib=3072,
        port_mappings= [ecs.PortMapping(container_port=8000, name="llmport8000")]
        
    )        
    
    # Import existing VPC
    existing_vpc = ec2.Vpc.from_lookup(self, "existing_vpc", vpc_id="")
    
    # Using Existing Security group id
    existing_security_group_id = ""
    existing_security_group = ec2.SecurityGroup.from_security_group_id(self, "ExistingSecurityGroup", existing_security_group_id)
    
    # Filter public subnets from the existing VPC
    public_subnets = [subnet for subnet in existing_vpc.public_subnets]
    cluster = ecs.Cluster(self, id="cluster", cluster_name="ecs_testing_cluster", vpc=existing_vpc)
    ebs_volume = autoscaling.BlockDevice(device_name="/dev/xvda", volume=autoscaling.BlockDeviceVolume.ebs(30))
    auto_scaling_group = autoscaling.AutoScalingGroup(self, "ASG",                                               
                                                    vpc=existing_vpc,
                                                    instance_type=ec2.InstanceType("t2.medium"),
                                                    machine_image=ecs.EcsOptimizedImage.amazon_linux2(),
                                                    min_capacity=1,
                                                    max_capacity=2,
                                                    block_devices=[ebs_volume], 
                                                    vpc_subnets= ec2.SubnetSelection(subnets=public_subnets),
                                                    security_group=existing_security_group,
                                                    key_name=""
                                                    
                                                )
                                                    
    capacity_provider = ecs.AsgCapacityProvider(self, "AsgCapacityProvider",
        auto_scaling_group=auto_scaling_group,
        instance_warmup_period=120,
        enable_managed_termination_protection= False
        
    )
    cluster.add_asg_capacity_provider(capacity_provider)        
    existing_alb = elb.ApplicationLoadBalancer.from_application_load_balancer_attributes(
        self, "MyExistingALB",
        security_group_id="sg-09a8f94cc420a7a00",
        load_balancer_arn="arn:aws:elasticloadbalancing:ap-south-1:005935583639:loadbalancer/app/practicewitheve/f22fa9e1f7146f48"
    )
    service = ecs_patterns.ApplicationLoadBalancedEc2Service(self, "MyService",
        cluster=cluster,
        task_definition=task_definition,
        desired_count=1,
        placement_strategies=[ecs.PlacementStrategy.spread_across_instances()],
        load_balancer=existing_alb,
        #load_balancer_name="cdkloadbalancer",
        #protocol= elb.ApplicationProtocol.HTTPS,
        #redirect_http=True,
        min_healthy_percent=100,
        max_healthy_percent=200,
        record_type= ecs_patterns.ApplicationLoadBalancedServiceRecordType.NONE,
        health_check_grace_period=cdk.Duration.seconds(60)
    )
    
    target_group = elb.ApplicationTargetGroup(
        self, 
        id="MyTargetGroup",
        target_group_name="cdkllm",
        vpc=existing_vpc,
        port=80,
        protocol=elb.ApplicationProtocol.HTTP,
        deregistration_delay=10,
        health_check=elb.HealthCheck(
            healthy_threshold_count=2,
            interval=cdk.Duration.seconds(10),
            path="/docs",
            unhealthy_threshold_count=2
        ),
        target_type= elb.TargetType.INSTANCE
    )
    
    service.listener.add_target_groups(target_groups=[target_group])
    target_group.add_target(service)
    
    service.listener.add_action(
        id="llmaction",
        action=elb.ListenerAction.forward(target_groups=[target_group]),
        conditions=[
            elb.ListenerCondition.host_headers(["recommendation.practicewitheve.ai"])
        ],
        priority=1
        
    )
    `

Error

Traceback (most recent call last): File "/Users/vishal/Documents/hello-cdk/app.py", line 9, in <module> EcsCdkStack(app, "EcsCdkStack", File "/opt/homebrew/Caskroom/miniforge/base/envs/cdk/lib/python3.9/site-packages/jsii/_runtime.py", line 118, in __call__ inst = super(JSIIMeta, cast(JSIIMeta, cls)).__call__(*args, **kwargs) File "/Users/vishal/Documents/hello-cdk/hello_cdk/hello_cdk_stack.py", line 88, in __init__ service = ecs_patterns.ApplicationLoadBalancedEc2Service(self, "MyService", File "/opt/homebrew/Caskroom/miniforge/base/envs/cdk/lib/python3.9/site-packages/jsii/_runtime.py", line 118, in __call__ inst = super(JSIIMeta, cast(JSIIMeta, cls)).__call__(*args, **kwargs) File "/opt/homebrew/Caskroom/miniforge/base/envs/cdk/lib/python3.9/site-packages/aws_cdk/aws_ecs_patterns/__init__.py", line 7282, in __init__ jsii.create(self.__class__, self, [scope, id, props]) File "/opt/homebrew/Caskroom/miniforge/base/envs/cdk/lib/python3.9/site-packages/jsii/_kernel/__init__.py", line 334, in create response = self.provider.create( File "/opt/homebrew/Caskroom/miniforge/base/envs/cdk/lib/python3.9/site-packages/jsii/_kernel/providers/process.py", line 365, in create return self._process.send(request, CreateResponse) File "/opt/homebrew/Caskroom/miniforge/base/envs/cdk/lib/python3.9/site-packages/jsii/_kernel/providers/process.py", line 342, in send raise RuntimeError(resp.error) from JavaScriptError(resp.stack) RuntimeError: Can only call addTargets() when using a constructed Load Balancer or an imported Load Balancer with specified vpc; construct a new TargetGroup and use addTargetGroup