API Gateway vs ALB: choose the request boundary before the backend

Proposed flow for this scenario

1. 1Client request
2. 2Chosen API or listener boundary
3. 3Route and integration or target group
4. 4Backend permission and health
5. 5Application response

This flow describes a design to evaluate. The local experiment explores one stated mechanism. Its scope appears with the controls; the proposed services are not provisioned.

Decision checkpoints

Start with the contract, not the compute label

LetX needs a small job-submission API returning an operation ID. QuantumSketch serves a long-lived web application from container tasks. List the route, authorization, request transformation, deployment and operational requirements for each before choosing a front door.

“Lambda means API Gateway, containers mean ALB” is an incomplete rule. Real ALB supports Lambda targets, and API Gateway offers supported private integration paths to load balancers. Those capabilities do not mean every combination is suitable or that this console implements them.

Name the API Gateway product

HTTP APIs and REST APIs differ. Features such as API keys, per-client throttling and request validation belong in a product-specific comparison, not a generic API Gateway checklist. Check the current AWS feature matrix for the chosen API type and required integration.

For this simulator, the supported API is an HTTP API with selected Lambda proxy routing and deployment snapshots. A local request diagnostic checks route selection and invocation permission. It does not provide a public endpoint, real authorization, a REST API, VPC Link or an actual network request.

ALB makes target health a visible boundary

An ALB listener selects a rule and forwards to a target group. The useful diagnostic distinguishes an unmatched intended route, missing registration, unhealthy targets, a blocked network path and an application response. Customer authorization remains an application or explicitly configured listener responsibility.

The local ALB exercise models selected HTTP routing and health decisions. Read its scope before assuming HTTPS, authentication, arbitrary target types or advanced rules. A running EC2 instance is not automatically registered, listening on the target port or passing the configured health path.

Compare operational failures through the consoles

In the LetX HTTP API exercise, configure a Lambda integration without its modeled invoke permission, inspect the failed integration request, repair the permission and repeat it. The backend may exist while the front door is still unable to invoke it.

In the ALB exercise, inspect the chosen listener action and target group, then break the target path or health behavior and recheck. These are different failure categories. Increasing desired capacity cannot fix a shared wrong port, health path or permission relationship.

Cost and the changed requirement

Question: LetX introduces per-customer API keys and request validation. Should you assume the existing HTTP API has those features? No. Revisit the product feature requirements and alternatives. Separately, an API key should not be confused with a complete end-user authorization system.

Estimate request volumes, payloads, transfer, connection patterns and supporting backend costs using current pricing. A request-based charge and a capacity-oriented load-balancer bill cannot be ranked without workload inputs. The network experiment below illustrates a path decision, not a throughput or billing benchmark.

Practice the supported console workflow

• Trace an HTTP API Lambda integration

  Uses simulated resources stored on this device. No website account or AWS credentials required.

  Explore ↗

• Inspect listeners and target groups

  Uses simulated resources stored on this device. No website account or AWS credentials required.

  Explore ↗

• Inspect function invocation results

  Uses simulated resources stored on this device. No website account or AWS credentials required.

  Explore ↗

Sources and scope

Reviewed against these official references. The model’s supported scope appears alongside its controls.

• AWS: HTTP API versus REST API feature matrix
• AWS: Application Load Balancer components and targets