[Thaxll]

Because why would you do that? Now we have tool and pipeline where testing / deploying ect .. is easy, so I'm not sure why would I risk to do hot load things.

I don't think it's useful and I think it's pretty dangerous is the first place. You have code that can run two different things, wcgw.

[Jtsummers]

Addressed in part by dmitriid and dnautics, but:

1. You can use this during development (where the tight feedback loop is very nice).

2. You can use this during deployment (after verifying that the process will work as intended, hopefully).

(1) is something you could do every day if it was your daily driver language. (2) would happen less frequently (well, as frequently as you deploy) but permit you to do partial updates without bringing the whole system down.

It's worth remembering that deploying Erlang (and Elixir) can be more like deploying with microservices or applications to an application server. You don't want to bring the whole thing down just to change out one part of the system, so you can update just the parts that have changed and need to be updated.

[dmitriid]

A very erlang demo showed upgrading code running on a telephone switch without dropping the call. That's why you want hot code loading.

[Thaxll]

Because control plane does not handle anything phone related most likely? It's like upgrading Kubernates masters, your API servers still works and are not affected.

AFAIK Erlang code does not handle any network traffic, all of that is done in C/C++.

[dmitriid]

This is the original video in its 90s glory: https://www.youtube.com/watch?v=uKfKtXYLG78

Regardless of where the call is handled, you can't just deploy a new switch in a telecom network, but you still want to upgrade them. This is where you really want hot code loading.

[yetihehe]

Real world usage case - I have a server which handles several thousand telematic devices (telemetry+actuation), split into about 20 different device types. It's small device base so doesn't require multiple servers and we can be really cheap. But requiring to disconnect all devices just to make one small change to one device driver would be painful. Now we can have uptime of over half a year and in that time we had changes/fixes to several drivers. Normally that would require scheduled downtime every week and slow us down considerably.

[dnautics]

I think (could be wrong) it's used for hot code reloading in phoenix when you're in dev mode. Make a change in your code, hit refresh in the browser, and now the relevant code deltas are applied to your http request.

[RobertKerans]

Someone correct me if I'm wrong here, but afaics dropping the ability to do it would remove a complication from the platform and wouldn't affect the vast majority of users in any way. But [afaik] it has to exist because Ericsson require that feature. Outside of their specific usecases it's doesn't seem a particularly useful feature, or one that is used in the vast majority of contemporary codebases