Proposed flow for this scenario

  1. Public client
  2. Internet-facing ALB listener
  3. Listener rule and target group
  4. Private target address and port
  5. Application response
  6. Return path

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

ChoiceFits whenWatch for
Internet-facing ALB + private targetsCustomers need a public front door while workers stay privately addressed.Adding public target addresses to repair a health-check fault.
Internal ALBOnly clients with the appropriate private network access should reach the service.Expecting its private addresses to create an internet front door.
Outbound NAT or supported endpoint pathPrivate targets need separately defined outbound dependencies.Assuming inbound ALB delivery automatically supplies internet egress.

Keep inbound delivery and outbound access separate

A synthetic QuantumSketch web worker accepts customer requests on port 8080 and needs no direct public address. The internet-facing load balancer supplies the public listener. Its forwarding path reaches the worker’s private address, so adding a public IP to the worker does not follow from the inbound requirement.

The worker may still need outbound access to retrieve dependencies or call another service. That requirement has its own route, endpoint or NAT design. A successful ALB request proves neither internet egress from the worker nor administrative access to it.

Describe both network paths before adding rules

For the public IPv4 design, choose suitable public ALB subnets across Availability Zones and the intended internet-facing scheme. Inspect listener port and client access separately from target-group port and health-check path.

Restrict the target security group to the intended load-balancer source where the design supports a group reference. The load-balancer rules must also permit its required target and health-check traffic. Network ACLs are an additional stateless boundary, so account for requests and replies rather than copying a single inbound rule.

A running target can remain unusable

Registration, process listening and health are separate states. An instance that is running can listen on the wrong port, reject the health path or fail the network check. Inspect the selected listener action and target group before assuming the frontend routes to the worker you expected.

In a real deployment, compare target reason codes with application logs and network evidence. A health endpoint should indicate the readiness required for routing without turning every transient noncritical dependency fault into complete loss of service. Passing it still does not prove every customer transaction succeeds.

Run an intentional fault and a narrow repair

Build the selected IPv4 VPC/subnet/ALB/target workflow in the console. Start with a known target port, inspect the registration and local health result, then remove the modeled target access or introduce a health failure. Predict which path should fail before running the diagnostic.

Repair that boundary while keeping the worker privately addressed, then inspect the return to health. The console exercises selected metadata and network decisions; it does not start a web server, send live packets, negotiate HTTPS or prove all current ALB routing features.

Keep a small evidence table during the drill: listener selected, target selected, target state and first failing network decision. Change one setting at a time and preserve the result. That prevents a broad collection of new rules from concealing which boundary actually caused the failure or leaving unnecessary exposure after recovery.

The changed requirement

Question: QuantumSketch can serve requests through the ALB, but its private worker cannot download a dependency. Should you open the worker’s inbound port to the internet? No. That changes the wrong direction. Inspect its outbound dependency path, authorization and the dependency’s availability.

Budget for the load balancer, application capacity, transfer and any supporting outbound network components with current regional pricing. The network experiment below illustrates route and rule logic, not a real throughput test. Private addressing narrows exposure; it does not replace application authentication or authorization.

Practice the supported console workflow

SimAWS · ShahriarLabs

Predict it. Test it. Change one thing.

Local educational model. No account or cloud charges. Nothing is deployed to AWS.

Path and controls
WorkerPrivate route → NAT → Public routeInternetReply is checked separately. Client/return address: 203.0.113.10; modeled port: 49152.

sim.shahriarlabs.com · Free to explore

Sources and scope

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

How we review explanations