Why do people create virtualenv in a docker container?

You can build a container with Dockerfile in a few seconds. Then why do people need to install a virtual enviroment inside the docker container?

It’s like a “virtual machine” in a virtual machine ?

Answer

I am working with virtualenvs in Docker and I think there are several reasons:

1. you may want to isolate your app from system’s python packages
2. you may want to run a custom version of python but still keep the system’s packages untouched
3. you may need fine grain control on the packages installed for a specific app
4. you may need to run multiple apps with different requirements

I think these are all reasonably good reasons to add a little pip install virtualenv at the end of the installation! :)