Upgrade to AE 19.0 from AE 17.5

We wanted to know while upgrading from AE 17.5 to AE 19.0 , do we need separate servers. I mean weather both AE 17.x and AE 19.x components can co-exist in same server while upgrading. One of our existing Client is not planning to spend extra for infra to migrate from 17.5 to 19.0.

Any migration document or lesson learnt document on migration from 17.x to 19.x would be great to start with.