KPHP is a web server

The architecture is quite usual: one master process which performs service operations, and many worker processes that handle incoming HTTP requests.

architecture

Master process duties:

  1. On start, open HTTP port, or in case of graceful restart take them from the server, which is being shut down.
  2. Manage worker processes:
    • create workers on start,
    • stop and remove workers on shutdown,
    • check workers availabilities,
    • collect worker processes stats,
    • restart hanged or dead workers.
  3. Collect server stats, aggregate stats from workers, and push everything into statsd service.
  4. Handle service queries (check option --http-port/-H), e.g. /server-status.

Worker processes do:

  1. Serve incoming HTTP requests — actually, they execute your PHP code.
  2. Write simple short log messages about incoming queries.
  3. On any warnings or errors, write corresponding messages into stderr and JSON log.

One worker can serve one request at a time. Until a request is finished, the worker doesn’t accept a new one.

Typically, you'd launch N workers on a production server, where N is a bit smaller than the number of CPU cores. Check option --workers-num/-f.
For development, 2 workers are enough.

When the server is launched from root, it switches to the user kitten, as working from root is a bad practice. You can override it by ./server -u {username} or even allow working from root by ./server -u root