Building a Simple Service Gateway With Amazon ECS Gateway

Long-running operations should usually be handled asynchronously rather than keeping an HTTP request open for an unpredictable amount of time.

Handle Service Failures

Backend services will occasionally fail.

A gateway should return controlled responses rather than exposing internal errors directly.

For example:

Gateway
   |
   v
Order Service
   |
   X
Unavailable
   |
   v
Gateway
   |
   v
503 Service Unavailable

Do not expose:

• Internal hostnames

• Stack traces

• Database errors

• Internal configuration

• Sensitive request information

The client should receive an appropriate public error response.

Avoid Retry Storms

Retries can make service failures worse.

For example:

Client
   |
   v
Gateway
   |
   +-- Request 1 -> Service fails
   +-- Retry -> Service fails
   +-- Retry -> Service fails

If thousands of requests behave this way, a recovering service can become overloaded.

Use retries carefully and consider:

• Limited retry counts

• Backoff

• Jitter

• Retry only safe operations

• Circuit-breaking strategies where appropriate

Do not automatically retry every HTTP request.

Add Request Correlation

Distributed systems are difficult to troubleshoot without request identifiers.

A gateway can assign or propagate a correlation ID:

Request
  |
  v
Gateway
  |
  | Correlation ID: abc-123
  v
Order Service
  |
  | abc-123
  v
Database / Logs

Then logs from different services can be connected to the same request.

For example:

gateway.log
request_id=abc-123 route=/api/orders

order-service.log
request_id=abc-123 order_id=1001

payment-service.log
request_id=abc-123 payment_id=5001

This becomes extremely useful when diagnosing production failures.

Validate Health Checks

The gateway needs a reliable way to determine whether backend services are available.

A health endpoint might look like:

GET /health

The service can return:

{
  "status": "healthy"
}

Health checks should be designed carefully.

A health check that performs expensive database operations every few seconds can create its own operational problem.

Separate basic process health from deeper dependency health when appropriate.

Protect Against Large Requests

The gateway is a useful place to enforce request limits.

For example:

Maximum request body: 5 MB
Maximum header size: defined limit
Request timeout: defined limit

These limits should reflect actual application requirements.

Do not set extremely large limits simply to avoid request failures.

Large requests can increase memory usage and make denial-of-service conditions easier to trigger.

Centralize Observability

A gateway sees traffic across multiple services, making it useful for centralized observability.

Track:

• Request count

• Response status

• Request latency

• Backend latency

• Timeout count

• Retry count

• Authentication failures

• Route-specific error rates

For example:

/api/orders
Requests: 100,000
5xx errors: 0.8%
p95 latency: 220 ms

/api/payments
Requests: 50,000
5xx errors: 1.2%
p95 latency: 410 ms

These metrics can help identify which service is causing problems.

Avoid Turning the Gateway Into a Monolith

A gateway can become difficult to maintain if business logic is continuously added to it.

Avoid putting logic such as:

Calculate order discount
Validate payment rules
Calculate inventory allocation
Generate invoices

inside the gateway.

Instead:

Gateway
   |
   +-- Routing
   +-- Authentication
   +-- Request controls
   +-- Observability
   |
   v
Business Service
   |
   +-- Business logic

This keeps service ownership clear.

Common Mistakes

Hard-Coding Task IP Addresses

ECS tasks can change during deployments and scaling.

Use service discovery and stable service endpoints instead.

Exposing Every ECS Service Publicly

A gateway should normally provide the controlled external entry point while backend services remain appropriately isolated.

Trusting Client Identity Headers

Never treat arbitrary client-provided identity headers as authenticated information.

Retrying Every Failed Request

Retries can increase load during an outage.

Use limited retries with appropriate conditions.

Putting Business Logic in the Gateway

Keep business rules inside the service that owns them.

Using Unlimited Timeouts

A slow backend can consume gateway resources if requests are allowed to remain open indefinitely.

Ignoring Correlation IDs

Without request tracing, distributed troubleshooting becomes significantly harder.

Troubleshooting Common Problems

Gateway Cannot Reach an ECS Service

Check:

• Network configuration

• Security groups

• Service discovery

• Target health

• Listener configuration

• Port mappings

• Container port

• Application binding address

A container listening only on localhost may not be reachable from another service.

For example, the application should generally listen on an appropriate network interface inside the container rather than only on the loopback interface.

Requests Return 404

Check:

• Gateway route

• Request path

• HTTP method

• Service path

• Route precedence

A gateway route can be correct while the backend expects a different path.

Requests Return 503

Check:

• Backend task health

• Service discovery

• Network connectivity

• Container availability

• Timeouts

• Load balancing configuration

A 503 from the gateway does not necessarily mean the application itself is broken. The gateway may simply be unable to reach a healthy backend.

Gateway Returns 504

A 504 commonly indicates that the gateway waited for a backend response and timed out.

Check:

• Backend processing time

• Database latency

• Network latency

• Gateway timeout

• Service timeout

• External dependencies

Do not simply increase the timeout without identifying why the service is slow.

Best Practices

Keep the Gateway Small

Use the gateway for communication concerns rather than application business rules.

Use Private Service Networking

Expose only the endpoints that actually need public access.

Define Explicit Routes

Keep routing rules predictable and easy to review.

Use Correlation IDs

Make request tracing consistent across services.

Apply Timeouts

Every network boundary should have a reasonable timeout.

Handle Failures Gracefully

Return controlled responses and avoid exposing internal details.

Protect the Gateway

Authentication, authorization, request limits, TLS, and monitoring should be part of the gateway design.

Design for Scaling

Do not depend on fixed task addresses or static service counts.

Advantages of an ECS Service Gateway

A gateway can provide:

• A single application entry point

• Better service isolation

• Centralized routing

• Easier client integration

• Consistent authentication handling

• Centralized observability

• Better control over backend exposure

• Easier service scaling

It can also simplify future changes because clients do not need to know the internal structure of the ECS environment.

Disadvantages and Considerations

A gateway also introduces another infrastructure component.

You need to consider:

• Additional configuration

• Gateway availability

• Monitoring

• Network latency

• Security management

• Routing complexity

• Operational cost

A poorly designed gateway can become a bottleneck or single point of failure.

For this reason, the gateway itself should be deployed with appropriate availability and scaling.

When a Simple Gateway Is a Good Fit

A service gateway is useful when:

• Multiple ECS services need a controlled entry point

• Clients should not know internal service locations

• Authentication and routing need centralization

• Services are expected to scale independently

• The architecture benefits from centralized observability

For a very small application with one backend service, adding a gateway may provide little benefit.

Summary

A service gateway can provide a clean communication boundary for applications running multiple services on Amazon ECS.

The basic architecture is straightforward: clients communicate with the gateway, and the gateway routes requests to the appropriate ECS services. The more important work is designing the operational and security boundaries around that routing layer.

Keep backend services appropriately private, use service discovery instead of hard-coded task addresses, define explicit routes, configure timeouts, handle failures carefully, and use correlation IDs for distributed troubleshooting.

Authentication can be centralized at the gateway, but backend services should still enforce authorization for sensitive operations.

Most importantly, keep business logic out of the gateway. A good gateway should make service communication easier without becoming another application monolith.