Docker Daemon

Docker daemon is the core service that handles all container operations. The docker CLI only acts as a client to communicate with the docker daemon.

Docker daemons are just JSON APIs

Docker daemons are just JSON APIs but exposed over a Unix socket.

The docker CLI writes JSON requests to the docker daemon socket, and the docker daemon reads these requests, processes them, and writes JSON responses back to the socket.

Listen on multiple sockets

By default, docker daemon listens on a Unix socket located at /var/run/docker.sock. See Unix Domain Sockets for more details.

But this can be changed to configured to listen on TCP sockets as well. In this case, even remote docker clients can connect to the docker daemon over the network.