ECS, ALB and API Gateway

Create ECS Cluster and Application Load Balancer

1. Access the VSCode Workspace
   • Create a new directory named cdk-workshop-02
   • Enter cdk-workshop-02
   • Init new python CDK project

2. Go to file cdk-workshop-02/cdk_workshop_02_stack.py, import these libraries

from aws_cdk import (
  Stack,
  aws_ecs as ecs,
  aws_ecs_patterns as ecsp,
  aws_apigateway as apigateway
)
from constructs import Construct

3. In cdk-workshop-02/cdk_workshop_02_stack.py, declare a ECS cluster together with Application Load Balancer in the __init__() function

      # Declare a Load Balancer Fargate 
      lb_fargate_service = ecsp.ApplicationLoadBalancedFargateService(
				self, 
				"Workshop02-MyWebServer",
        task_image_options=ecsp.ApplicationLoadBalancedTaskImageOptions(
            image=ecs.ContainerImage.from_registry("nginxdemos/hello")
        ),
        public_load_balancer=True,
        desired_count=3
      )

ecsp.ApplicationLoadBalancedFargateService will create the following resources:

• A new VPC with default configuration (subnet, Internet Gateway, RouteTable, EIP, Nat Gateway, …)
• A ECS cluster in the newly created VPC, running on Fargate
• An ECS Task defined by the nginxdemos/hello image from Dockerhub
• A ECS container group initiated from the ECS Task, with the number of instances is 3
• A Application Load Balancer fronting the ECS cluster
• Needed roles and security groups

Configure API Gateway

4. Declare an API Gateway

# Define API Gateway
api = apigateway.RestApi(self, "ProxyToLBECS")

5. Configure API Gateway resource to point to the DNS of the Application Load Balancer

# Get the DNS value of the Application Load Balancer 
lb = lb_fargate_service.load_balancer
lb_dns = lb_fargate_service.load_balancer.load_balancer_dns_name

# Add resource and method for proxy request
proxy = api.root.add_resource("ecs")
proxy.add_method("GET", apigateway.HttpIntegration(f"http://{lb_dns}"))

You can read more about the methods and properties of ApplicationLoadBalancedFargateService at the official CDK documentation of AWS (Python)

6. Check the code in cdk-workshop-02/cdk_workshop_02_stack.py

from aws_cdk import (
    Stack,
    aws_ecs as ecs,
    aws_ecs_patterns as ecsp,
    aws_apigateway as apigateway
)
from constructs import Construct

class CdkWorkshop02Stack(Stack):

    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)
        
        # Declare a Load Balancer Fargate 
        lb_fargate_service = ecsp.ApplicationLoadBalancedFargateService(
          self, 
          "Workshop02-MyWebServer",
          task_image_options=ecsp.ApplicationLoadBalancedTaskImageOptions(
              image=ecs.ContainerImage.from_registry("nginxdemos/hello")),
          public_load_balancer=True,
          desired_count=3
        )
        
        # Define API Gateway
        api = apigateway.RestApi(self, "ProxyToLBECS")
        
        # Get the DNS value of the Application Load Balancer 
        lb = lb_fargate_service.load_balancer
        lb_dns = lb_fargate_service.load_balancer.load_balancer_dns_name
        
        # Add resource and method for proxy request
        proxy = api.root.add_resource("ecs")
        proxy.add_method("GET", apigateway.HttpIntegration(f"http://{lb_dns}"))

Setup virtual environment for python

Before we deploy, we must

• Setup a virtual environment in cdk-workshop-02 directory, because our EC2 instance has 2 versions of python, we have to isolate them to make sure there aren’t conflicts between python’s packages.
• Install packages in requirements.txt

1. Install virtualenv
   • Back to /home/ec2-user

pip3.9 install virtualenv

8. Change directory back to cdk-workshop-02
   • Setup a virtual environment in venv
   • Active virtual environment in to venv/bin/activate

virtualenv venv
source venv/bin/activate

9. Install all required packages in requirements.txt

pip install -r requirements.txt

Deploy

10. Verify the resources that would be created by running

cdk diff

11. Before we deploy this stack, we have to boostrap our environment

cdk boostrap

12. Then we deploy the stack

cdk deploy

Choose y to continue

13. Finish and test result

Access the link to the API Gateway (ProxyToLBECSEndpoint), add the path /ecs. You will be able to access the webserver deployed in ECS.

To verify that the ALB works properly, hit refresh a couple of times, and you will see the target of the website change. In the previous section, we set the parameter desired_count=3, so there will be 3 containers being deployed in parallel behind the ALB. You will notice the change in the field Server address between the refreshes.

If you have reached this state, congratulations on finishing the first part of the CDK basic 2 Workshop. In the next section, we will use CDK to deploy a Lambda function behind an API Gateway resource.