Build a small TA-Lib container image

To make a small enough container image is a complicated job, especially Python.
We can use multi-stage build process and virtualenv to reduce the overhead from the build and pip install.
However, some Python libraries use the runtime C library, we have to overcome this issue; otherwise the package won’t work.
I will take TA-Lib as an example to show how to get everything done correctly.

Here is an example, and there are 5 points should be aware:

1. Choose a small enough base image; nevertheless, avoid using alpine. The reason is explained by this article: https://pythonspeed.com/articles/alpine-docker-python/
2. Multi-stage is a good idea to reduce the overhead of building processes. In addition, applying virtualenv makes things much more easily. Therefore, install all Python packages into /opt/venv.
3. Now, we can try to build TA-Lib from the source. You have to specify the installation path to /opt/venv as well while configure.
4. Because we moved the default library path to /opt/venv, we need assign the global option or the build option to pip to let it know the library path.
5. Finally, remember to provide the LD_LIRARY_PATH to let python know where are the shared libraries.

Following the above procedure, the image size will be around 250MB. This is pretty small.