Author here, thanks for sharing ! Happy to answer any questions.
I think the article outlines it, but I'm at very low scale, with custom development for every client. I mostly build mini-figmas, collaborative or not, that automate specific document pipelines on top of my software, backed by elixir+liveview (or elixir+vue+channels).
It's also the best ecosystem for indie/small team development. With a handful of well-established libraries, one can go a long way without having to reach for separate/dedicated queue/messaging systems, job or workflow orchestrations, even spinning up an ephemeral machine just to run heavy workloads is not complex. Frameworks like Ash make an entire category of server applications a matter of a few declarative modules.
I know a team using it to replace ancient massive mainframe based systems with modern distributed systems and the gist is that the language is fine, but mostly ideal for use cases that leverage the ErlangVM or BEAM stack.
The downside they run into is the ecosystem isnt there, at least a couple guys wish they had just used Kotlin/Java for library interoperability with so much existing code already built and battle tested for specific purposes.
I think that's a good point. Our largest pain point with Elixir is definitely the size of the community and the associated dearth of niche libraries. The technology behind it, though, is solid enough that once those libraries exist, things really take off. My team wrote several open source medical libraries for Elixir and we've seen it really expand into the healthcare market.
We run a large distributed cluster (currently 4 DCs spanning the US) and use hot code reload for live patches when needed and rolling deployments for our standard releases.
Hot code reloading for development (recompile-on-save) has issues, but production hot code loading for zero-downtime deployments is still a core BEAM strength and what this article focuses on.
I'm not using this to update the app itself - which is a docker container that gets updated when I push a new version. I'm simply using the BEAM's code loading capabilities to add client-specific parts to the app while it is running. They are part of the monorepo (and thus part of the app at dev time), but get stripped at build-time so they can be selectively loaded later.
Elixir removed a jankier https://www.erlang.org/doc/apps/sasl/appup.html mechanism that defined how state is upgraded or downgraded, while watching a directory and recompiling a module automatically or manually from the repl is still common
> while watching a directory and recompiling a module automatically or manually from the repl is still common
That makes it sound like the "hot" part has been removed then, and it's just basically a "live reload" rather than "hot code loading", is that right? There is no persistent state and you get a fresh one after the automatic compilation happened?
I've used utility functions in Erlang where I make changes, then compile and load all modified modules...
It's absolutely hot loading, there's persistent state, any fully qualified function calls run in the newest module. The gen_server pattern always calls into your behavior module with fully qualified calls, so those are pretty easy to get into new code at a reasonable time. If you write your own service loop, it's pretty common to call ?MODULE:loop() to enable hotloading there too.
There's footguns; hotloading is a way to make rapid changes to your system, but sometimes rapid changes isn't what's needed and sometimes the rapid change you make is to go from a partially broken system to a fully broken system. But, there's a virtuous circle when you can make production changes quickly, because you can make a small change and observe and make many follow ups in a single day. With push processes that take a long time, you end up encouraged to make a bigger change one time, otherwise you spend all day waiting for traffic to move between old and new versions, or waiting for instances to deploy, etc.
queued messages stay around in the mailboxes, so no state is lost, but don't get migrated/transformed/versioned via the appup mechanism, unless you opt back into it via libraries for it like https://github.com/ausimian/castle
Overall, it's not widely used nor pushed (blue green deployments are now very common), but it still has interesting uses.
For instance, very high availability without blue-green (using a front-end that can be hot-patched), or... musical endeavors (such as live reloading code that generates music, on the go) https://youtu.be/_VgcUatTilU?si=DDfe4FN3Nw9OzRhF&t=122
Author here, thanks for sharing ! Happy to answer any questions.
I think the article outlines it, but I'm at very low scale, with custom development for every client. I mostly build mini-figmas, collaborative or not, that automate specific document pipelines on top of my software, backed by elixir+liveview (or elixir+vue+channels).
Elixir is the best general purpose programming language for distributed systems.
It's also the best ecosystem for indie/small team development. With a handful of well-established libraries, one can go a long way without having to reach for separate/dedicated queue/messaging systems, job or workflow orchestrations, even spinning up an ephemeral machine just to run heavy workloads is not complex. Frameworks like Ash make an entire category of server applications a matter of a few declarative modules.
What makes you say that? Honestly asking.
I know a team using it to replace ancient massive mainframe based systems with modern distributed systems and the gist is that the language is fine, but mostly ideal for use cases that leverage the ErlangVM or BEAM stack.
The downside they run into is the ecosystem isnt there, at least a couple guys wish they had just used Kotlin/Java for library interoperability with so much existing code already built and battle tested for specific purposes.
I think that's a good point. Our largest pain point with Elixir is definitely the size of the community and the associated dearth of niche libraries. The technology behind it, though, is solid enough that once those libraries exist, things really take off. My team wrote several open source medical libraries for Elixir and we've seen it really expand into the healthcare market.
I thought elixir devs have cooled on the whole hot reload update or is this different?
We run a large distributed cluster (currently 4 DCs spanning the US) and use hot code reload for live patches when needed and rolling deployments for our standard releases.
Hot code reloading for development (recompile-on-save) has issues, but production hot code loading for zero-downtime deployments is still a core BEAM strength and what this article focuses on.
I'm not using this to update the app itself - which is a docker container that gets updated when I push a new version. I'm simply using the BEAM's code loading capabilities to add client-specific parts to the app while it is running. They are part of the monorepo (and thus part of the app at dev time), but get stripped at build-time so they can be selectively loaded later.
Elixir removed a jankier https://www.erlang.org/doc/apps/sasl/appup.html mechanism that defined how state is upgraded or downgraded, while watching a directory and recompiling a module automatically or manually from the repl is still common
> while watching a directory and recompiling a module automatically or manually from the repl is still common
That makes it sound like the "hot" part has been removed then, and it's just basically a "live reload" rather than "hot code loading", is that right? There is no persistent state and you get a fresh one after the automatic compilation happened?
I've used utility functions in Erlang where I make changes, then compile and load all modified modules...
It's absolutely hot loading, there's persistent state, any fully qualified function calls run in the newest module. The gen_server pattern always calls into your behavior module with fully qualified calls, so those are pretty easy to get into new code at a reasonable time. If you write your own service loop, it's pretty common to call ?MODULE:loop() to enable hotloading there too.
There's footguns; hotloading is a way to make rapid changes to your system, but sometimes rapid changes isn't what's needed and sometimes the rapid change you make is to go from a partially broken system to a fully broken system. But, there's a virtuous circle when you can make production changes quickly, because you can make a small change and observe and make many follow ups in a single day. With push processes that take a long time, you end up encouraged to make a bigger change one time, otherwise you spend all day waiting for traffic to move between old and new versions, or waiting for instances to deploy, etc.
queued messages stay around in the mailboxes, so no state is lost, but don't get migrated/transformed/versioned via the appup mechanism, unless you opt back into it via libraries for it like https://github.com/ausimian/castle
Overall, it's not widely used nor pushed (blue green deployments are now very common), but it still has interesting uses.
For instance, very high availability without blue-green (using a front-end that can be hot-patched), or... musical endeavors (such as live reloading code that generates music, on the go) https://youtu.be/_VgcUatTilU?si=DDfe4FN3Nw9OzRhF&t=122
That seems more about loading dynamic code.