openssh-server doesn't start in Docker container

I am having a weird problem.

I am not able to ssh to docker container having ip address 172.17.0.61.

I am getting following error:

$ ssh 172.17.0.61
ssh: connect to host 172.17.0.61 port 22: Connection refused

My Dockerfile does contain openssh-server installation step:

RUN apt-get -y install curl runit openssh-server

And also step to start ssh:

RUN service ssh start

What could be the issue?

When I enter into container using nsenter and start ssh service then I am able to ssh. But while creating container ssh-server doesn't seems to start.

What should I do?