Channels: Mock sink server #4409
Description
User story
We need a configurable test target that simulates real-world sink behaviours so we can test the proxy under realistic conditions during development and in CI.
Details
A Plug app or standalone script that can be started locally and configured to simulate various sink responses: delays, status codes, auth rejection, timeouts, large response bodies, and mixed behaviour patterns. Reusable for ongoing development and CI.
Implementation notes
Dependencies: None — can be built independently.
Blocks: #4410 (K6 load tests)
Release notes
N/A — internal test tooling.
User acceptance criteria
- Configurable response delay (0-30s)
- Configurable response status codes (200, 4xx, 5xx)
- Configurable response body size (up to several MB)
- Auth rejection mode (returns 401/403)
- Timeout mode (never responds)
- Mixed behaviour mode (e.g., 80% fast 200s, 20% slow 503s)
- Can be started locally with a single command