ECS with ALB integration in AWS - Step-by-Step Execution

Process Flow - ECS with ALB integration

Create ECS Cluster

↓

Define Task with Container

↓

Create ALB (Application Load Balancer)

↓

Create Target Group for ALB

↓

Configure ALB Listener to Forward to Target Group

↓

Create ECS Service with ALB Integration

↓

ECS Service Registers Tasks to Target Group

↓

ALB Routes Incoming Traffic to ECS Tasks

↓

Users Access Service via ALB

This flow shows how ECS tasks are connected to an Application Load Balancer to route user traffic to running containers.

Execution Sample

AWS

1. Create ECS Cluster
2. Define Task with container image and port
3. Create ALB and Target Group
4. Set ALB Listener to forward to Target Group
5. Create ECS Service linked to ALB Target Group

This sequence sets up ECS with ALB to route traffic to container tasks.

Process Table

Step	Action	Resource Created/Updated	State Change	Result
1	Create ECS Cluster	ECS Cluster	Cluster active	Ready to run tasks
2	Define Task Definition	Task Definition	Task registered	Container image and port set
3	Create ALB	Application Load Balancer	ALB active	Listening for traffic
4	Create Target Group	Target Group	Target group active	Ready to register targets
5	Configure ALB Listener	ALB Listener	Listener active	Forwards to Target Group
6	Create ECS Service with ALB integration	ECS Service	Service active	Tasks launched and registered to Target Group
7	Tasks register to Target Group	Target Group	Targets healthy	Ready to receive traffic
8	ALB routes traffic	ALB	Traffic forwarded	Users access containers via ALB
9	Exit	N/A	N/A	Setup complete, service accessible

💡 All resources created and ECS tasks registered to ALB target group; traffic routing active

Status Tracker

Resource	Initial	After Creation	After Configuration	Final State
ECS Cluster	None	Created	Active	Active
Task Definition	None	Defined	Registered	Registered
ALB	None	Created	Listener Configured	Active with Listener
Target Group	None	Created	Targets Registered	Healthy Targets
ECS Service	None	Created	Tasks Running	Active with Tasks
Tasks	None	Launched	Registered to Target Group	Healthy and Serving

Key Moments - 3 Insights

Why do ECS tasks need to register with the ALB target group?

Because the ALB uses the target group to know where to send incoming traffic. Without registration, the ALB cannot route requests to the running containers. See execution_table step 7.

What happens if the ALB listener is not configured to forward to the target group?

The ALB will not know where to send traffic, so requests will fail. Listener configuration is essential to connect ALB to ECS tasks. See execution_table step 5.

Can ECS tasks run without an ALB?

Yes, but without an ALB, you must manage task IPs and ports manually. ALB simplifies routing and load balancing. This is why ALB integration is common. See overall concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table at step 6. What is the state of the ECS Service after creation?

A Service active with tasks launched and registered

B Service created but no tasks running

C Service inactive

D Service deleted

💡 Hint

Refer to execution_table row with Step 6 under 'State Change' and 'Result'

At which step does the ALB start forwarding traffic to ECS tasks?

A Step 4

B Step 8

C Step 5

D Step 2

💡 Hint

Check execution_table for when traffic forwarding is active

If the target group is not healthy, what will happen to user traffic?

A Traffic will be routed normally

B ALB will create new tasks automatically

C Traffic will fail to reach ECS tasks

D ECS service will stop

💡 Hint

See variable_tracker row for Target Group final state and execution_table step 7

Concept Snapshot

ECS with ALB integration:
- Create ECS Cluster and Task Definition
- Create ALB and Target Group
- Configure ALB Listener to forward to Target Group
- Create ECS Service linked to ALB Target Group
- ECS tasks register to Target Group
- ALB routes user traffic to running containers

Full Transcript

This visual execution shows how to connect AWS ECS with an Application Load Balancer (ALB). First, an ECS cluster is created to run containers. Then, a task definition specifies the container image and port. An ALB is created to handle incoming traffic. A target group is made for the ALB to send traffic to ECS tasks. The ALB listener is configured to forward requests to this target group. An ECS service is created that launches tasks and registers them with the target group. Once tasks are healthy and registered, the ALB routes user traffic to these containers. This setup allows users to access containerized applications through the ALB, which balances load and manages traffic routing automatically.

Practice

1. What is the main purpose of integrating an Application Load Balancer (ALB) with Amazon ECS?

easy

A. To distribute incoming web traffic evenly across multiple container tasks

B. To store container images securely

C. To monitor CPU usage of ECS tasks

D. To create virtual private clouds automatically

Solution

1. Step 1: Understand ALB role in ECS

   ALB is designed to balance incoming traffic to multiple targets, such as ECS tasks, to ensure reliability and scalability.

2. Step 2: Identify the correct purpose

   Among the options, only distributing web traffic evenly matches ALB's function in ECS.

3. Final Answer:

   To distribute incoming web traffic evenly across multiple container tasks -> Option A

4. Quick Check:

   ALB balances traffic = C [OK]

Hint: ALB balances traffic to containers, not stores or monitors [OK]

Common Mistakes:

• Confusing ALB with container image storage
• Thinking ALB monitors CPU usage
• Assuming ALB creates VPCs

2. Which ECS launch type and network mode combination is recommended for simple networking and security when using ALB?

easy

A. EC2 launch type with none network mode

B. EC2 launch type with bridge network mode

C. Fargate launch type with host network mode

D. Fargate launch type with awsvpc network mode

Solution

1. Step 1: Recall recommended ECS and network mode

   Fargate with awsvpc mode provides each task with its own network interface, simplifying networking and security.

2. Step 2: Match options to recommendation

   Only Fargate launch type with awsvpc network mode matches the recommended combination for ALB integration.

3. Final Answer:

   Fargate launch type with awsvpc network mode -> Option D

4. Quick Check:

   Fargate + awsvpc = A [OK]

Hint: Fargate + awsvpc = simple networking with ALB [OK]

Common Mistakes:

• Choosing EC2 launch type instead of Fargate
• Using bridge or host network modes with Fargate
• Selecting none network mode which disables networking

3. Given this ECS service configuration snippet, what will happen when the ALB receives HTTP requests?

{
  "loadBalancers": [{
    "targetGroupArn": "arn:aws:elasticloadbalancing:...",
    "containerName": "webapp",
    "containerPort": 80
  }],
  "launchType": "FARGATE",
  "networkConfiguration": {
    "awsvpcConfiguration": {
      "subnets": ["subnet-12345"],
      "assignPublicIp": "ENABLED"
    }
  }
}

medium

A. ALB forwards requests to the webapp container on port 80 in each task

B. ALB blocks all HTTP requests due to missing security group

C. ALB forwards requests to port 443 by default

D. ALB cannot route because containerPort is missing

Solution

1. Step 1: Analyze load balancer target settings

   The ALB targets the container named "webapp" on port 80, so it will forward HTTP requests there.

2. Step 2: Check network configuration

   Fargate with awsvpc and public IP enabled allows tasks to receive traffic from ALB.

3. Final Answer:

   ALB forwards requests to the webapp container on port 80 in each task -> Option A

4. Quick Check:

   ALB targets container port 80 = B [OK]

Hint: ALB forwards to specified containerPort, not default 443 [OK]

Common Mistakes:

• Assuming ALB blocks traffic without explicit security group mention
• Thinking ALB defaults to port 443
• Missing containerPort causes routing failure

4. You deployed an ECS service with ALB integration but the ALB shows no healthy targets. What is the most likely cause?

medium

A. The ECS cluster has no EC2 instances running

B. The ALB listener is missing a rule for HTTPS traffic

C. The ECS tasks are not registering with the target group due to incorrect container port mapping

D. The ALB is in a different AWS region than the ECS service

Solution

1. Step 1: Understand why ALB shows no healthy targets

   ALB health checks fail if ECS tasks do not register correctly, often due to wrong container port mapping.

2. Step 2: Evaluate other options

   Listener rules missing HTTPS won't cause no healthy targets; ECS Fargate doesn't need EC2 instances; ALB and ECS must be in same region, but this is less common cause.

3. Final Answer:

   The ECS tasks are not registering with the target group due to incorrect container port mapping -> Option C

4. Quick Check:

   Incorrect port mapping blocks target registration = A [OK]

Hint: Check container port matches target group port for healthy targets [OK]

Common Mistakes:

• Assuming missing HTTPS rule causes no healthy targets
• Thinking ECS Fargate needs EC2 instances
• Ignoring region mismatch issues

5. You want to deploy a highly available ECS service behind an ALB that automatically scales with traffic. Which combination of settings ensures this best practice?

hard

A. Use EC2 launch type with none mode, ALB with health checks disabled, and ECS service with fixed task count

B. Use Fargate launch type with awsvpc mode, ALB with target group health checks, and ECS service auto scaling

C. Use Fargate launch type with host mode, ALB with fixed target group size, and no ECS scaling

D. Use EC2 launch type with bridge mode, ALB without health checks, and manual ECS task scaling

Solution

1. Step 1: Identify best ECS launch and network mode for availability

   Fargate with awsvpc mode simplifies networking and security, ideal for high availability.

2. Step 2: Confirm ALB and ECS scaling features

   ALB target group health checks ensure traffic only goes to healthy tasks; ECS service auto scaling adjusts task count with traffic.

3. Step 3: Evaluate other options

   Other options lack health checks or auto scaling, reducing availability and scalability.

4. Final Answer:

   Use Fargate launch type with awsvpc mode, ALB with target group health checks, and ECS service auto scaling -> Option B

5. Quick Check:

   Fargate + awsvpc + ALB health checks + auto scaling = D [OK]

Hint: Combine Fargate, awsvpc, ALB health checks, and auto scaling [OK]

Common Mistakes:

• Skipping ALB health checks
• Using manual scaling instead of auto scaling
• Choosing EC2 with bridge or none network modes