I've used docker run -it to launch containers interactively and docker run -d to start them in background. These two options seemed exclusive. However, now I've noticed that docker run -dit (or docker run -itd) is quite common. So what is the difference? When -it is really needed together with -d?
Yes, sometimes, it's necessary to include -it even you -d
When the ENTRYPOINT is bash or sh
docker run -d ubuntu:14.04 will immediately stop, cause bash can't find any pseudo terminal to be allocated. You have to specify -it so that bash or sh can be allocated to a pseudo terminal.
docker run -dit ubuntu:14.04
If you want to use nano or vim with any container in the future, you have to specify -it when the image starts. Otherwise you'll get error. For example,
docker run --name mongodb -d mongo
docker exec -it mongodb bash
apt-get update
apt-get install nano
nano somefile
It will throw an error
Error opening terminal: unknown.