New View of Microservices

We haven't measured the actual time. I would say the time learning Elixir has not been a hurdle or anyway limiting factor to the projects we are working on.

We basically switched as a company from writing servers in C#/nodejs/python to just Elixir. Did this gradually during end of last year and this spring.

Though I must mention that all of our developers were already familiar with multiple languages. And since we have multiple projects going on we can transfer knowledge easily. So YMMV.

Learning the procedural aspects of Erlang or Elixir is very easy. In that sense I agree with the previous responses. Erlang gets a lot of bad rap for the syntax. But, it is really no more difficult that any other language to learn. The syntax can easily be learned in a day. Elixir's syntax can be learned even more quickly because it looks a lot like Ruby or Python. Thus, you can certainly start write scripts in Erlang or Elixir relatively quickly. My guess is that the average, experienced developer could start writing basic scripts in an hour or two. However, those scripts would be entirely procedural in nature, unless they are already very familiar with functional programming and pattern matching.

The first hurdle in Erlang/Elixir is the functional aspects of the language and understanding the power of pattern matching. Both of these require rethinking how you build a program. But, both of these are also incredibly, incredibly worthwhile and powerful. Elixir in particular is a great medium for better understanding these concepts because it is a very approachable language. Getting over this hurdle did not happen over night for me. I rarely used recursion in Ruby or Javascript (there is no tail call optimization). On the other hand, in functional languages recursive functions are the norm. I learned to really love them with Erlang/Elixir and now it frustrates me when I can't use them elsewhere because it has become much easier for me to reason about recursive functions than loops. Overall, functional programming and pattern matching are amazing things to learn but really grokking them won't happen over night.

The next hurdle with Erlang/Elixir is understanding OTP. This is THE incredibly powerful aspect of the Erlang VM. However, it is also not an easy subject matter to approach unless you already have a strong background in distributed systems. I did not. Hence, it took me a while to compose programs that actually used the Erlang VM for what it was built for, OTP. Thus, this portion of the Erlang/Elixir learning curve felt long and slow. I was not used to spawning new processes on a whim and passing messages back and forth. Initially I would send messages only one way without realizing that the appropriate pattern is to view it in a standard server-client relationship where there should always be a request and a response. Eventually I started viewing all the little applications running inside my larger program as self-contained capsules/servers that communicated among each other. However, it took me weeks of really intense study to get comfortable with. But, once you get comfortable with OTP you have a lot of built-in power (people rarely mention Mnesia, DTS, ETS gen_server but they are awesome).

Overall, my experience with Erlang/Elixir has shown me one big thing: pick the best tool for the job and there are a lot of jobs that you don't need OTP for. When you need to build Whatsapp, you should pick Erlang/Elixir. When you want to build a simple web app that only has a couple of end points and much of the dynamism is handled on the front-end, use Go, Node, or my personal favorite Clojure. Erlang/Elixir shine in the context for which they were built. But, they are not built for everything. And, if you only want the procedural aspects of the languages, there is no reason to choose them over Go, Node, Clojure, or Scala...all of which have solid approaches to concurrency.

And what about a monolithic system executing thousands of different functions?

If your app is a simple todo list, sure, go monolithic (but you should still delegate storage to some other tool). If it is much more complex than a todo list, then it is very likely that you have many packages containing many modules developped and maintained by many programmers. And if one glitch on one side of the monolith affects a remote module and functionalities depending on it, or even breaks down the whole monolith, then you should go microservices. Or split your code base. Or do whatever is needed so the thing can still move forwards, if slowly, without breaking apart at each little step.

Seriously though, all of the problems breaking the system up will be blamed on people who already left the company, whether they deserve it or not, and the patterns that keep you in a monolith will continue on forever.

The only solution I've seen sort of work for this is to make a single binary, but create modules with extremely clear boundaries. Even so far as compiling them separately if the language is statically typed. But even that can go sideways the moment someone builds caching into the system.

I've come to appreciate why external caches are so popular, but for my money I prefer caching at the HTTP layer. You have to solve all the same problems, but you get one level of cache for free, it's easier for QA to understand, and it puts cache eviction in the hands of mature pieces of code that all implement the same spec (which might account for my previous point).

Pass by reference became de rigeur for high performance systems when we agreed that the message passing overhead represented the plurality of computation time.

But pass by reference is shared state, and as we started trying to build systems with threading and for multiple cores the ugly truth about memory coherence on modern processors came out. It was pretty bad. Java and later C had to come up with some pretty odd looking compromises to get safety without throwing away all of the speed advantages.

I guess what bugs me is not the mind changing (I do that all the time myself). It's that those without a history lesson behave as if this is a bloody revolution, and they have to pick sides. And the people who think switching solutions will magically fix all of our problems.