How to connect to a running container created with Docker?

There are several ways:

1. Docker attach: Connects your terminal's standard input, output, and errors to the main process of the container.

   docker attach <container_id_or_name>
   

   • Pros: Easy to use, instant connection to the main process.
   • Cons: Exiting the session (Ctrl+C) may stop the main process of the container. Not suitable for running individual commands inside the container.

2. Docker exec: Runs a new command inside a running container and attaches a terminal to it. Ideal for interactive work (shell) or executing scripts.

   docker exec -it <container_id_or_name> <command>
   

   • The -it parameter enables interactive mode (-i) and pseudo-TTY allocation (-t).
   • <command> is the command to execute inside the container, most often bash or sh.

   docker exec -it my_web_server bash  # Connects to bash inside the container
   docker exec my_db_container ps aux # Executes `ps aux` and outputs to the current terminal
   

   • Pros: Does not stop the main process of the container upon exit. Allows executing any commands inside the container. The most common method for debugging and maintenance.
   • Cons: Starts a new process inside the container.

3. SSH Server inside the container: A more complex approach that requires installing and configuring an SSH server inside the container image. Allows connecting to the container like a regular virtual machine or server via SSH protocol.

   • Pros: Standard and familiar management method. Safer for production management (with proper configuration).
   • Cons: Complicates the container image. Requires SSH server setup and key/password management. Violates the "one process per container" Docker paradigm if the main process is not SSH.

Recommendation: For most debugging and interactive work, the most suitable and safe method is docker exec -it.