Elixir releases are a subset of distillery that’s correct. Currently there’s a bunch of overlap in functionality, as distillery basically had/has to do all the stuff elixir releases do. Especially as it’s still used for elixir <1.9 projects. Distillery also does more than elixir core releases. Most notably is the support for hot code updates in distillery.

As for when to use which: If you’re on elixir 1.9 (possibly without distillery already) I’d use core releases unless you need features only distillery provides. I’ve also heard people in slack note that elixir releases seem smaller than distillery ones, but I cannot confirm that, but might be worth looking into if file size is a concern.

I’d not try to mix them, as they are similar, but also very different: e.g. the cli in bin/ is completely different. Instead of changing distillery though I’d rather hope that distillery’s functionality will over time be extracted in (possibly smaller, more purpose build) new libraries, which hook into core releases using the :steps configuration available. I’m not sure how well this is possible for e.g. hot updates, but I’d expect adding things like build hooks or custom cli commands should be possible this way.

You want one or another, I think. I was sort of forced to switch to 1.9 releases because stumbled upon bugs with distillery + erlang + elixir in most recent versons. Which is a recurring pattern, and something to expect from external library.

Elixir releases are now internal part of Elixir, which means the chances are they won’t break as much on updating as distillery did. There’s absolutely no blame on distillery side, it’s just that carrying about multiple Elixir versions is obviously more difficult than carrying about one single current Elixir version. So the code base is in several places overcomplicated / bug prone because of that requirement, I suppose.

I was pleasantly surprised with the migration. I am very happy with how runtime config is handled. I kind of miss deploy hooks not being there but easy to work around, and probably for the best.

So in the long run, I think Elixir releases are the way to go for pretty much everyone. I suspect there’ll be a way to extend them with tools built on top of them, rather than distillery soon, so if you need some of the missing functionality you’ll be able to add it this way.