[majidazimi]

Consider for some reason (either technical or political), this company decides to migrate their web socket servers to Akka/Rust/Go/NodeJS. Integrating these new servers into their core cluster is going to be deadly painful. They rely heavily on Erlang/OTP internal clustering. This is not even considered as a challenge in distributed systems but still really painful to implement because of their design decision. This is what they did wrong. Clustering and message routing part of the application should be technology agnostic.

[jlouis]

It isn't that hard. I have code which lets an OCaml program speak the Erlang distribution protocol. It can more or less stand-in for an Erlang node in the distribution layer. Writing the same for another language shouldn't be that hard: the protocol spoken is a simple prefix-protocol which can be parsed with LL(1) from the head plus an atom cache that is easy to maintain.

That said, good Erlang architectures definitely knows when you should fan out and use a common layer for distribution. At $work we have a Kafka cluster for some event handling simply because it is the right tool for the job, and because it makes it easier to interface other programs on top of it.

In my experience, the distribution features are best used as orchestration however. Your distribution layer is Erlang, and then you use other languages for "leaves" in the architecture. If the right library is present in e.g., Go, then by all means use it. Erlang easily speaks protobuf for instance.

[brightball]

That depends what you're going for. Moving web sockets elsewhere are pretty simple regardless of whether you're using Erlang/OTP or not because it's a frontal layer. If you do that all you are doing is creating another layer to hold connections that needs to relay to the rest of the application. The application behind it still has the responsibility to receive and relay everything from those web sockets, determine what message goes to who, etc.

You can move it out just the same as you can elsewhere, you just add an unnecessary layer of complexity and lose a lot of the capabilities already built into the language. It boils down to a simple question of, what would be the purpose behind that decision? What improvement would you get from deciding to move any of that elsewhere? Do you gain speed at the cost of complexity?

Clustering is a non-trivial problem. It can't happen naturally in any language that includes mutable data without explicit oversight and thus most of the needed tooling can't be built into the system and guaranteed to work everywhere. As soon as some part of the system goes from "send message, get response" to "send message, change variable referenced in memory on this machine, get response" you break your ability to naturally cluster.

That leads to a dependency in central relay points for things like setting up web sockets and then having code behind them communicate. The code behind them in whatever language is usually going to be talking to other central relay points like load balancers or pub sub databases rather than directly to other specific servers.

As soon as you have central relay points, they become something else that you have to monitor and scale even if they are very high volume.

There's nothing wrong with this approach and it will certainly work but if you want to avoid that and build a distributed system in another language, you've got to invest a lot in other areas.

[majidazimi]

> Moving web sockets elsewhere are pretty simple regardless of whether you're using Erlang/OTP or not because it's a frontal layer.

It is supposed to be easy. But they are not using language agnostic messaging. Instead they rely on Erlang distribution protocol. This is what makes it difficult to integrate.

> what would be the purpose behind that decision?

1. To achieve composability. I can replace one web socket server with a C++ implementation to see if I can handle 10 million connections per server. If I fucked it up return back to Erlang implementation otherwise fuck BEAM. I'm moving to native code. The beauty of it is that I can do it one step at a time. Even I can implement web socket layer in multiple languages and experiment all possible options in production and no one even notices it.

2. I don't have to pay for 20 Erlang guys who are mostly senior devs. Get 5 of them to write the core and the rest of the team NodeJS guys.

[mononcqc]

You're acting like the distribution and serialization formats of Erlang are not open or documented.

If you're going for your C++ layer, try https://github.com/saleyn/eixx for example.