feat(elbv2): honor preserve_host_header parameter

[jvdsande]

Summary

Hello!
This PR updates the ELBv2 service to honor the preserve_host_header parameter.

It propagates the load balancer's ARN through the ElbV2DataPlane instance in order to retrieve the current value of routing.http.preserve_host_header.enabled in executeForward/proxyRequest

Type of change

• Bug fix (fix:)
• New feature (feat:)
• Breaking change (feat!: or fix!:)
• Docs / chore

AWS Compatibility

Change tested with a simple echo server running on ECS behind an ALB.

Stack deployed through terraform with hashicorp/aws 6.57.1.

Without the patch/with preserve_host_header=false:

curl \                                               
  -H 'Host: example.com' \
  http://localhost:8088/
{"host":"172.17.0.3:8080"}

With the patch + preserve_host_header=true:

curl \
  -H 'Host: example.com' \
  http://localhost:8088/
{"host":"example.com"}

Checklist

• ./mvnw test passes locally
• New or updated integration test added
• Commit messages follow Conventional Commits

[github-actions]

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[greptile-apps]

Greptile Summary

The PR adds support for the ELBv2 routing.http.preserve_host_header.enabled attribute and verifies both its default and enabled behavior.

• Propagates the listener and load-balancer identity through forward-action processing.
• Reads the current load-balancer attribute for each forwarded request.
• Preserves the inbound Host header when enabled and otherwise continues using the target authority.
• Adds an end-to-end integration test covering runtime attribute changes.

Confidence Score: 5/5

The PR appears safe to merge, with the new host-header behavior covered through the real ELBv2 data-plane path.

The listener resolves its owning load balancer, each forward reads the current attribute value, and the integration test confirms both disabled and enabled behavior without exposing a concrete regression.

Important Files Changed

Filename	Overview
src/main/java/io/github/hectorvent/floci/services/elbv2/ElbV2DataPlane.java	Propagates listener ownership into forwarding and conditionally retains the inbound Host header based on the live load-balancer attribute.
src/test/java/io/github/hectorvent/floci/services/elbv2/ElbV2PreserveHostHeaderIntegrationTest.java	Adds an integration test proving default target-host forwarding and immediate client-host preservation after enabling the attribute.

Sequence Diagram

sequenceDiagram
    participant Client
    participant DataPlane as ELBv2 Data Plane
    participant Service as ELBv2 Service
    participant Backend
    Client->>DataPlane: Request with original Host
    DataPlane->>Service: Read load-balancer attributes
    Service-->>DataPlane: preserve_host_header value
    alt Preservation enabled
        DataPlane->>Backend: Forward with original Host
    else Preservation disabled
        DataPlane->>Backend: Forward with target Host
    end
    Backend-->>DataPlane: Response
    DataPlane-->>Client: Proxied response

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