[AlphaWeaver]

People may "prefer" simply replacing containers, but as some siblings mention, some applications might require more reliability guarantees.

Erlang was originally designed for implementing telephony protocols, where interrupted phone calls were not an acceptable side effect of application updates.

[AnotherGoodName]

FWIW as soon as you start using containers you should be able to handle those containers spinning up/down. Pretty much the whole point of containers. At which point you don’t need to bother with code hot swapping since you already have a mechanism for newer containers to spin up while older ones spin down.

The sibling post “that’s how they update without downtime” is super naive. It is absolutely not how they do it.

[Muromec]

That's kinda what erlang does, just on a different level. Your docker and your load balancer are both inside your app.

[simoncion]

If we to wedge how Erlang does hot code swapping into a container metaphor, then to get what Erlang does, you'd need to have a container per function call.

Given that it would be absurdly wasteful to use OS processes in containers to clone Erlang's code reload system, AnotherGoodName might take ten minute to watch Erlang: The Movie to get a better sense of the capabilities of that system. The movie is available from many places, including archive.org.

[Muromec]

>If we to wedge how Erlang does hot code swapping into a container metaphor, then to get what Erlang does, you'd need to have a container per function call.

You have a container that responds to HTPP requests sitting behind a load balancer, then you spawn a new container and tell load balancer to redirect calls to the new one. From the point of view of whoever is calling the load balancer you have hot swapping. You may even separate containers into logical groups and call it microservices architecture. Or you can define a process as something having qualified name and a mailbox and is sending messages to other processes.

Now reasonable people may disagree about what's wasteful, but the market seems to tolerate places where adding a checkbox to a form is a half a year process involving five different departments and the market can't be wrong.

[simoncion]

Sure, you can shut down and restart your entire application. You could do that back in 1990 without containers, too.

The thing is that Erlang does hot reload at a per-function (or -according to Hebert- sometimes more-fine-grained) level, so nuking the entire program and paying the cost to start it up again is not at all the same thing as -say- using a not-absurdly-priced AWS Lambda [0] or similar to get per-function hot reloading.

By the way, have you read "A Pipeline Made of Airbags"? If not, you should give it a read: <https://ferd.ca/a-pipeline-made-of-airbags.html>. It might be old news to you, maybe, but maybe not.

[0] Good luck finding one, though.

[Muromec]

I didn't read that one before, but I share the sentiment. We can't have cool things and it was all dumbed down, so the worst case become a default mode of operation. This didn't happen specifically with hot reload in erlang, it happens all the time at all levels.