Understanding Nginx’s Three Process Types: Master, Worker, and Cache

Master Process

The master process starts when Nginx launches and handles communication with the outside world as well as managing internal processes.

Main responsibilities

Read and validate configuration files.

Create, bind, and close sockets.

Generate, manage, and terminate worker processes according to configuration.

Receive commands such as restart, upgrade, or shutdown.

Perform seamless reloads and upgrades without service interruption, and roll back on failure.

Open log files and acquire file descriptors.

Worker Process

Generated by the master process, the number of worker processes is defined in the configuration and they live for the entire lifetime of the master.

Main responsibilities

Accept incoming requests.

Pass requests through various functional modules for filtering.

Perform I/O operations to obtain response data.

Communicate with backend servers and receive processed results.

Cache data, access cache indexes, query and retrieve cached content.

Send the final response back to the client.

Receive commands from the master process such as restart, upgrade, or shutdown.

Cache Process

There are two types of cache processes.

Cache index rebuilding process

Created by the master process after Nginx starts; it exits automatically once the cache metadata reconstruction is complete. It scans the cache directory structure and builds an in‑memory index database.

Cache index management process

Exists for the entire lifetime of the master process and is responsible for determining whether cached metadata has expired after updates.