Learning term
Host rule — Reverse proxies and routing
Host rule decides from host or path which router handles a request. This card shows its role in “Reverse proxies and routing” and a safe diagnostic path.
Orientation
Host rule decides from host or path which router handles a request. At this level, separate purpose, input, and visible result. Place Host rule within Reverse proxies and routing before changing settings or files.
Practical use
Test the exact Host header and path when the default site answers instead of the intended service. Start in a sandbox with neutral examples. Record the expected state, make one controlled change, and compare status output, application behavior, and logs.
Technical understanding
Host rule decides from host or path which router handles a request. Technically, Host rule connects through interfaces, configuration, state, or dependencies. Trace data from input to output and check versions, permissions, networking, storage, and resources separately.
Operations and debugging
Test the exact Host header and path when the default site answers instead of the intended service. In production-like operations, use measurable signals, least privilege, reproducible configuration, and a documented rollback. Preserve evidence, isolate the cause, and verify the correction with the same test.
Exercise
Try it safely
Test the exact Host header and path when the default site answers instead of the intended service. Open an isolated test environment and run “curl -I -H "Host: app.example.com" http://127.0.0.1”. Write down the expected output first, do not alter production data, and record one safe next diagnostic step.
curl -I -H "Host: app.example.com" http://127.0.0.1Quick check
Can you explain the purpose, observable state, and most common failure source of Host rule — Reverse proxies and routing in one sentence each? Which evidence would you preserve before changing anything, and which repeated test would prove that the correction actually worked?