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ECS Service Discovery

5 minutes 5 Questions

Amazon ECS Service Discovery provides a mechanism for ECS services to locate and communicate with each other using DNS names. Instead of using hard-coded IP addresses, which can change as tasks scale, you can use service discovery to map a friendly DNS name to a service's tasks. AWS Cloud Map creat…

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AWS Certified Solutions Architect - ECS Service Discovery Example Questions

Test your knowledge of ECS Service Discovery

Question 1

You are deploying microservices on Amazon ECS. You need a managed, ECS-native service discovery solution that automatically registers and deregisters tasks as they start and stop, provides DNS-based discovery within the VPC, and optionally supports API-based lookups for service attributes. Which AWS service should you choose?

Correct Answer: AWS Cloud Map

AWS Cloud Map is the AWS-managed service discovery solution that natively integrates with Amazon ECS. When enabled on an ECS service, tasks are automatically registered and deregistered in a service registry backed by Cloud Map. It provides DNS-based discovery within your VPC (using Route 53 records that it manages) and optional API-based discovery (DiscoverInstances) with attributes for advanced use cases. In contrast, a Route 53 Private Hosted Zone alone is DNS-only and requires custom automation for lifecycle registration; “Amazon ECS Service Registry” is not a standalone AWS product; and an Auto Scaling group with target tracking is for scaling instances, not service discovery.

Question 2

You run multiple microservices on Amazon ECS in a private VPC. The services must discover and call each other using private DNS names that automatically update as tasks scale in and out, without exposing endpoints to the internet or provisioning a separate load balancer for each service. What is the best way to implement service discovery?

Correct Answer: Use ECS service discovery integrated with AWS Cloud Map (Route 53 private DNS) to register and resolve backend service endpoints

ECS integrates natively with AWS Cloud Map to provide DNS-based service discovery. When enabled, each ECS service registers its tasks in a Cloud Map namespace backed by Route 53 private hosted zones. Clients resolve a stable private DNS name that automatically reflects scaling events and task replacements, returning A/SRV records for healthy endpoints within the VPC. This meets the requirement for internal, private, dynamic discovery without exposing services publicly or standing up a separate load balancer for each service. VPC peering only provides network connectivity and does not offer discovery. Elastic Load Balancing gives a single DNS name per load balancer and is not a general-purpose service discovery mechanism, and using one load balancer per service is unnecessary overhead given the requirement. Deploying all services in a single ECS task is an anti-pattern that removes independent scaling and does not solve discovery.

Question 3

You have a containerized web application running in AWS ECS. You need to direct incoming traffic to the appropriate ECS service. What should you use?

Correct Answer: Application Load Balancer

For directing incoming traffic to the appropriate ECS service, you should use an Application Load Balancer. It supports path-based routing and can route requests to multiple services based on the request path. Other options like Classic Load Balancer and Network Load Balancer are not the best choices for containerized web applications, AppConfig is for managing app settings, API Gateway is for creating, maintaining, and securing APIs, and Cloud Map is for service discovery.

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