AWS ECS Services: Keeping Your Application Running 24/7

By Juan Ahumada | December 4, 2025 | Part 3 of 4 in the AWS ECS Series

What is an ECS Service?

An ECS Service is the component that ensures your application stays running. It takes a Task Definition and guarantees that a specified number of Tasks (running containers) are always up and healthy.

Why Do You Need a Service?

Without a Service, you'd have to manually:

• Start new Tasks when old ones fail
• Monitor the health of each Task
• Scale up during high traffic
• Scale down when traffic decreases
• Distribute traffic among multiple Tasks

A Service automates all of this for you, 24/7.

Key Features of ECS Services

1. Desired Count

You specify how many Tasks you want running at all times. If you say "3", the Service ensures 3 Tasks are always running.

• If a Task fails, the Service automatically starts a new one
• If you change the desired count, the Service adjusts accordingly

2. Load Balancing

Services can integrate with Application Load Balancers (ALB) or Network Load Balancers (NLB) to distribute incoming traffic across your Tasks.

3. Auto Scaling

Services can automatically adjust the number of running Tasks based on metrics like:

• CPU utilization: Scale up when containers are working hard
• Memory utilization: Scale up when memory usage is high
• Request count: Scale up when traffic increases
• Custom metrics: Scale based on your specific needs

4. Health Checks

Services constantly monitor Task health. If a Task fails a health check, it's automatically replaced. Health checks can be:

• Container health checks: Defined in the Task Definition
• Load balancer health checks: HTTP requests to verify the app responds

5. Rolling Updates

When you deploy a new version of your application, Services perform rolling updates:

1. Start a new Task with the updated Task Definition
2. Wait for the new Task to become healthy
3. Stop an old Task
4. Repeat until all Tasks are updated

This ensures zero downtime during deployments.

Service vs. Task: What's the Difference?

This is a common point of confusion, so let's clarify:

• Task: A single running instance of your containers (like one chef cooking)
• Service: The manager that ensures the right number of Tasks are always running (like the restaurant manager)

You can run Tasks without a Service (for one-time jobs), but for web applications that need to run continuously, you need a Service.

Creating Your First Service

Here's how to create a Service in the AWS Console:

1. Go to your ECS Cluster
2. Click "Create" in the Services tab
3. Select your Task Definition
4. Give your Service a name
5. Set the desired number of Tasks
6. Configure networking (VPC, subnets, security groups)
7. Optionally, configure a load balancer
8. Click "Create Service"

Common Service Configurations

For a Simple Web Application

• Desired count: 2-3 (for redundancy)
• Load balancer: Yes (ALB)
• Auto scaling: CPU-based, 2-10 Tasks

For a Background Worker

• Desired count: 1-2
• Load balancer: No (doesn't receive web traffic)
• Auto scaling: Based on queue depth

Key Concepts to Remember

• A Service ensures your application is always running
• It maintains a desired count of Tasks automatically
• Load balancing distributes traffic across Tasks
• Auto scaling adjusts capacity based on demand
• Health checks and rolling updates ensure reliability
• Services are essential for production workloads

What's Next?

Now that you understand Services, you're ready to learn about Tasks - the actual running instances of your containers. In the final article of this series, we'll explore how Tasks work, their lifecycle, and when to run Tasks directly vs. through a Service.