When using umbrella projects, adding a new Phoenix app may require a way of routing traffic from one HTTP(S) port to the different applications. This post explains the trade-offs of multiple solutions to that problem and what's the best one in their opinion
Elixir/Phoenix feels like Rails back in 2008 when we built one of the largest Rails app. It will take time for the community to develop.
That being said, my company has been using Elixir/Phoenix for three years and while many times there isn't a library for Elixir, often times there is already a stable Erlang library we can use.
We have also changed our habit from looking for third-party libraries to either building our own module which we discovered they are fairly easier to build than we thought, or coming up with alternate solutions that built on top of the powerful Elixir/Erlang technology (e.g. OTP).
Our company has been using Phoenix/Elixir since day 1. Most of our engineers have experience using Rails and they are productive in less than a few days.
The Elixir community is strong and once a while when we have questions, we are able to get a quick answer from the community.
After building products from scratch using Rails (on LinkedIn mobile), Go, and Elixir, which each product has served over tens of millions of people, I am very pleased with the decision using Elixir which we spent the less time in scaling.