> create a very large in memory read-only pd dataframe and then put a flask interface to operations on that dataframe using gunicorn and expose as an API. [...]

May I ask what you consider large memory - MByte, GByte, TByte? The simplest solution is to store it as a blob on a SSD, and read it via simple file IO or put it into a DB. But I assume this was too slow, so it would be interesting to go into more details.

In the end you can do shared memory with multiprocessing in Python, which - I have to admit - requires some setup and bookkeeping work.