Which one should i use? docker kill or docker stop?

Question

Will docker stop fail if processes running inside the container fail to stop?? If i use docker kill, can unsaved data inside the container be preserved. Is docker stop time consuming compared to docker kill?? I want to do a shutdown of the container but without loosing any data(without high latency to complete kill or stop process).

Answer 1

Line reference:

docker stop: Stop a running container (send SIGTERM, and then SIGKILL after grace period) [...] The main process inside the container will receive SIGTERM, and after a grace period, SIGKILL. [emphasis mine]

docker kill: Kill a running container (send SIGKILL, or specified signal) [...] The main process inside the container will be sent SIGKILL, or any signal specified with option --signal. [emphasis mine]

You can get more info from this post: https://superuser.com/questions/756999/whats-the-difference-between-docker-stop-and-docker-kill

Answer 2

Docker stop: When you issue a docker stop command a hardware signal is sent to the process inside of that container. In the case of docker stop we send a sig term message which is short for terminate signal its a message that's going to be received by the process telling it essentially to shut down on its own time.

SIGTERM is used any time that you want to stop a process inside of your container and shut the container down, and you want to give that process inside there a little bit of time to shut itself down and do a little bit of clean up.

A lot of different programming languages have the ability for you to listen for these signals inside of your code base, and as soon as you get that signal you could attempt to do a little bit of cleanup or maybe save some file or emit some message or something like that.

On the other hand the docker kill command issue is a sig kill or kills signal to the primary running process inside the container, so kill it essentially means you have to shut down right now and you do not get to do any additional work.

So ideally we always stop a container with the docker stop command in order to get the running process inside of it a little bit of time to shut itself down, otherwise if it feels like the container has locked up and it's not responding to the docker stop command then we could issue docker kill instead.

One kind of little oddity or interesting thing about docker stop, when issue docker stop to a container and if the container dose not automatically stop in 10 seconds then docker is going to automatically fall back to issuing the docker kill command.

So essentially at docker stop is us being nice but it's only got 10 seconds to actually shut down.

A good example could be ping command. sudo docker run busybox ping google.com now if you want to stop the container if you use docker stop container_id, you will see it takes 10 seconds before getting shut down because ping command dose not properly respond to a SIGTERM message. In other words the ping command doesn't really have the ability to say oh yeah I understand you want me to shut down.

So after we waited those 10 seconds eventually the kill signal was sent to it telling it hey ping you are done and shut yourself down.

But if you use docker kill container_id you are going to see that's it instantly dead.