As someone who worked with Erlang for a few of years I still wonder if using parallel processing in program top level is worth it or not. Because there are many ways to process data efficiently using queues, pipelines, etc and being clear on when it happens rather than a "wild west" of Erlang where you need to manage processes, links, restarts, and it's harder to focus on the business logic.
What do you mean with "process data efficiently"? You speak about performance? But the main goal of the design of Erlang is fault tolerance, not performance. You can still use queues or whatever in Erlang if you want, but having a fault-tolerant system with process tree and process supervision in other languages is a different story.
Right, I was mainly describing arguments for parallel processing which Erlang is also famous for.
In terms of being fault-tolerant I think the modern approach with (micro)services is quite similar, one can have multiple services running and communicating using something like protobuf, having restart strategies, fallbacks and so on. From my experience Erlang doesn't offer any killer features in this case, does it?
Erlang pushes kubernetes down into the language and its libraries, instead of requiring Docker images and containers, etc.
This means that the processes can be much, much more lightweight than kubernetes pods and containers. Cheaper to kill and restart. Can provide concurrency and fault tolerance at a far more granular level. Much simpler to write and deploy than Docker images. Etc. etc.
At least that's my understanding (significant work experience with kubernetes, no real production experience with Erlang/Elixir).
As an dev working in Elixir, you're right on the money. IMO, the biggest benefit you gain from that granularity is that since processes cost next to nothing to spin up and down, you can (ab)use your fault tolerance mechanism for error handling, leading to the famous "Let it crash" philosophy.
Restarting your docker image every time someone sends a malformed packet to your webserver is going to make for a trivial not even D-DOS attack. Killing the individual process that spins up to handle that particular packet/connection, though, is simply best practice.
Except you still need to run and deploy your Erlang app somewhere which might end up on Kubernetes.
Kubernetes is just better than Erlang for process managment because it does more and is completely language agnostic, imagine you can't build some part of your system in Erlang but you need the same kind of functionality what do you do?
You can make NIF, you can implement Erlang protocol to talk to the node (and I have done it). Both of those are possible but does it worth it in the end? Is it worth to have orchestration builtin into the language and locked with some particular features instead of a full-fledged devops setup?
The only argument I have is in early stages of development it might save some time.
The killer feature is that the fault-tolerant behaviour is something either implicit, builtin or bundled [Erlang/OTP] with the language, instead of something that you need to either reinvent or bolt yourself to both your own code and your dependencies code as a afterthought when things start to fail.
In Erlang the fault-tolerant behavior is not builtin either, only tools to make it. You still have to make the right supervision tree, dependencies between processes, links, making sure you handle the process termination messages correctly and many other details.
In my experience in non-Erlang setups while doing requests to other services you have to check the response status and add some code handling it, so it's not really a complete afterthought. The only difference I see here is that Erlang handles failure in a real-time way, but it also can be done using some periodic task to query important services. And implementing in outside of Erlang gives more flexibility (think of Erlang cluster size and network limitations)
Our team had worked on an Elixir app for a couple years, before splitting off game logic into Dotnet. Scaling the dotnet server was a much different beast:
- It wasn't designed to crash on failure. It uses thread pools with no supervision trees. We had to add in liveliness probes to check if it is alive. I've only had to use readiness checks for Elixir
- No REPL. With a REPL in production, we can debug things live, even try patches to see if those work. Can't do that with Dotnet. That's also something that contributes to reliability
Now, cluster size do matter. The way Erlang and BEAM was designed were for vertical scaling. You can minimize cluster size by biasing towards vertical scaling. That's what we do on our systems. There's a way to do that with Kubernetes so that we scale vertically during our daily traffic cycle.
At some point though, you start looking at partial clustering topology for BEAM, or use one of the many process registeries that are better suited for dynamic membership. (The one bitwalker wrote comes to mind).
That's wrong. Fault tolerance is basically the default. Yes you have to build a supervision tree, but unless you're writing a one-off script, you have to build it to anyways to do anything.
Well you confirming what I said - you have to build it, it's not that Erlang programs automatically never fail and always handle problem correctly as required.
>From my experience Erlang doesn't offer any killer features in this case, does it?
Yes the killer feature in this case (relative to microservices) is a sane deployment, single codebase, unified language, being able to do integration tests without a full DevOps team, etc.
I agree that Erlang has some benefits in the early stage of development or with smaller projects, but beyond that you anyway will need devops and this argument no longer holds. One example I have is whatsapp being started in Erlang by a few engineers and it was a huge success from engineering point of view, but later rewritten (I think in C++) anyways. They had their reasons but it's clear that something in Erlang was not satisfactory and fault-tolerance with distributed nature was not enough to stop it.
I'm talking about development, deployment should be automated anyways.
As a developer I think it's easier to think in terms of how to send data to hadoop, sqs queue etc for processing and read results later than keep in mind the supervision tree, messages, mailbox size, linking and so on. And the "processing" side can be as well implemented in Erlang just I don't feel Erlang's features are needed in the "top level development" and create more problems and barriers.
It is yes. When you just starting a project Erlang's approach might be favorable but once the whole infrastructure is there the difference is negligible.
