Setup service on ECS for login application

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Prerequisites

• Image pushed to ECR (copy its image URI).
• An ECS cluster (here, a production cluster).
• Appropriate VPC, subnets, and security groups configured for the ALB and ECS tasks.
• Port 5000 used by the Flask application.

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1. Create the Task Definition

1. Open the AWS Console and navigate to ECS.
2. Click Task Definitions → Create new task definition.
3. Give the task definition a descriptive name.
4. Scroll down to add a container:
   • Paste the image URI you copied from ECR into the container image field.
   • Add a port mapping: container port 5000.
   • Leave other settings at their defaults unless you need resource limits or environment variables.
5. Click Create.

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2. Create the Service from the Cluster

1. Go to Clusters and select your production cluster.
2. Click Create to create a new service.
3. Select the task definition you created for the login app.
4. Give the service a name such as login-app-microservice.

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3. Configure Load Balancing (Application Load Balancer)

• Under Load balancing, choose Application Load Balancer (ALB).
• You can select an existing load balancer or create a new one:
  • If creating new, give the ALB a name and set the idle timeout to 30 seconds.
  • Configure a listener for port 5000 and map it to the target group used by the ECS service.
• Ensure the target group uses the correct port (5000) and a health check path that your app responds to (e.g., / or /health).

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4. Wait for Deployment and Verify Health

• After creating the service, ECS launches tasks and registers them with the ALB target group.
• Wait until the service deployment becomes STABLE and the tasks report as healthy.
• If the deployment fails or stays unhealthy, check:
  • ECS service events for error messages.
  • Task logs in CloudWatch (or the container logs).
  • ALB target group health check results.
  • Security groups: ensure ALB can reach container port 5000 and the ALB has an inbound rule for the client port you will use.

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5. Validate the Application

1. In the ECS service page, click View Load Balancer for this service.
2. Copy the Load Balancer DNS name.
3. Open a browser and visit: http://<LOAD_BALANCER_DNS>:5000 (wrap the DNS placeholder in backticks as shown).

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Common ECS/ALB settings (recommended)

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Troubleshooting checklist

• Subnet selection error: ensure ALB subnets are public or reachable.
• ALB target health failing: check health check path and container response.
• No response in browser: verify security group inbound rules and that ALB is listening on the expected port.
• Task keeps restarting: inspect container logs for exceptions and verify environment variables, database connectivity, and required secrets.

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6. Fix the Flask redirect issue

from flask import Flask, redirect

app = Flask(__name__)

@app.route('/product')
def product():
    # Original (hardcoded external IP):
    # return redirect("http://35.156.49.246:5000/welcomepage")
    # Recommended: use a relative path (keeps redirects within the same host/load balancer)
    return redirect('/welcomepage')

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Next steps and best practices

• Use environment variables for service URLs and external endpoints rather than hard-coded values.
• Configure health checks that match actual application endpoints and response times.
• Centralize logs in CloudWatch and set up alerts for unhealthy targets or repeated task restarts.
• Consider using HTTPS with a certificate on the ALB for secure traffic.
• For production, consider placing tasks in private subnets and using the ALB in public subnets only.

• Amazon ECS documentation
• Amazon ECR documentation
• ALB documentation and target groups
• Flask documentation