CODEWITHSUNDEEP
dockerdocker-composedockerfile
trentjones21
trentjones21

Reputation: 571

How do you kill a docker containers default command without killing the entire container?

I am running a docker container which contains a node server. I want to attach to the container, kill the running server, and restart it (for development). However, when I kill the node server it kills the entire container (presumably because I am killing the process the container was started with).

Is this possible? This answer helped, but it doesn't explain how to kill the container's default process without killing the container (if possible).

If what I am trying to do isn't possible, what is the best way around this problem? Adding command: bash -c "while true; do echo 'Hit CTRL+C'; sleep 1; done" to each image in my docker-compose, as suggested in the comments of the linked answer, doesn't seem like the ideal solution, since it forces me to attach to my containers after they are up and run the command manually.

Upvotes: 4

Views: 4444

Answers (2)

TJ Zimmerman
TJ Zimmerman

Reputation: 3484

This is by design by Docker. Each container is supposed to be a stateless instance of a service. If that service is interrupted, the container is destroyed. If that service is requested/started, it is created. If you're using an orchestration platform like k8s, swarm, mesos, cattle, etc at least.

There are applications that exist to represent PID 1 rather than the service itself. But this goes against the design philosophy of microservices and containers. Here is an example of an init system that can run as PID 1 instead and allow you to kill and spawn processes within your container at will: https://github.com/Yelp/dumb-init

Why do you want to reboot the node server? To apply changes from a config file or something? If so, you're looking for a solution in the wrong direction. You should instead define a persistent volume so that when the container respawns the service would reread said config file.

https://docs.docker.com/engine/admin/volumes/volumes/

Upvotes: 5

BMitch
BMitch

Reputation: 263549

If you need to restart the process that's running the container, then simply run a:

docker restart $container_name_or_id

Exec'ing into a container shouldn't be needed for normal operations, consider that a debugging tool.

Rather than changing the script that gets run to automatically restart, I'd move that out to the docker engine so it's visible if your container is crashing:

docker run --restart=unless-stopped ...

When a container is run with the above option, docker will restart it for you, unless you intentionally run a docker stop on the container.

As for why killing pid 1 in the container shuts it down, it's the same as killing pid 1 on a linux server. If you kill init/systemd, the box will go down. Inside the namespace of the container, similar rules apply and cannot be changed.

Upvotes: 6

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