What is the limitation of Docker regarding running multiple processes inside a single container?

Docker by default is oriented towards running a single main process inside the container. This is because containers were originally designed as isolated environments for a single application or service. Running multiple processes inside a container complicates management, especially regarding signal handling, logging, and container shutdown.

The main limitation is that Docker tracks the state of the main process (PID 1 inside the container). If this process terminates, the container stops. Running multiple processes requires additional tools, such as init systems (supervisord, tini), to manage the lifecycle of processes inside the container.

Thus, the limitation is not technically the inability to run multiple processes, but that Docker does not provide built-in tools for managing them, which can lead to control and stability issues.