Actor Model Programming: Building Resilient Distributed Systems (with Hugh McKee)

The actor model is a popular approach to building scalable software systems. And isn’t hard to understand when you’re just reading about the beginner’s examples. But how do you architect a complex design using the actor model? Which patterns work well? How do you think through it?
Joining me to take us through it is Hugh McKee. Hugh’s a total actor-model fan, and a Developer Advocate for Lightbend (the company that created the popular actor framework Akka). He takes us from his definition of actors to the designs he’s worked on, the patterns he’s found most useful, and the interesting meeting-point between actor-based designs and event-based ones.

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[rightscript]

Hey Kris & Hugh, very nice! I've been purchasing books on the Actor Model. Checked out your book link and surprised by the gift. Big heart to you both ;)

[MattRockwell-fm]

Oh my. Spent 15 years as Tandem/NonSop Systems Programmer (TAL). What is old is “almost” new again. Super episode.

[AdrianBoyko]

You need to get one of the Pony language guys to talk about Pony’s approach. It’s probably the purest example of the Actor paradigm and is also notable for its use of reference capabilities which allow safe sharing of mutable data between actors.

[alihammadshah]

This interviewer is great. Such good questions.

[devsuvara]

I use event streaming and actors in one project. In many ways, I find the event streaming method to be conceptually easier to understand. It just fits nicely with the idea of a single pipe on information being handled sequentially.

Yet, in some cases, the procedural flow of an actor is actually a better and clearer approach.

Both have a place. The best outcome is having a system is modular and easy enough to change with out breaking. :)

[tqwewe]

Absolutely loved this video! It resonates deeply with my recent work. I just developed a basic event log database that appends data in 256 MB segments and allows services to subscribe to new events. It's everything I need and incredibly fast. I'm using it alongside an actor library I built to design my startup, which is being developed with event sourcing.

[osman]

I ALWAYS thought Actor Model is way better that microservices so I am so glad and expert just said the same :)

[rivotuksammel]

Amazing! Crazy that it only has 10k views.

[JH-pero]

I've become convinced that actors solve a localized problem of organizational boundaries and responsibilities, but they don't solve the scaling, which is still primarily subject to Conway's Law - the purpose of moving around all that data is mostly because of human factors. When you scale you end up in a position of configuring actor behavior; the configuration becomes the program, and if the program does not employ a central coordination method like a pipeline, graph or constraint solver(e.g. flow-based programming) you end up with problems managing buffers and queues and synchronizations. When Hugh describes a tree structure emerging, it's natural and unsurprising because memory hierarchies would dictate that kind of algorithm. When he describes event streams being logged centrally, it reflects the need for coordination. As well, because you're using a configuration mechanism and not the tooling of a general-purpose programming language, you end up with the bug classes associated with extension programming.

Log-structuring is the new deal that is interesting, and we can do it now since we can throw a lot of compute at stuff. The overall shape of what he suggests - AI agents with learned behavior communicating over event logs - starts to sound conspicuously like blockchain, minus the financialized emphasis. When you take away the self-interested human trader and install an AI with different reward functions it's more reasonable to find the broad applications.

[tanuj]

Its a very informative conversion
I have one question on actor model
Let asy I have a order system which I have designed using Actor state machine
My order system also need to expose data to customer or UI about total orders and there status
So how do we add the Query capabilities in this Actor model

[LewisCampbellTech]

20:23 I swear the more I get into computing, the more everything seems to come back to 1) the Actor Model and 2) Event Sourcing.

[britneyshamk]

Would love to see an interview someone from Holochain. They are building an agent-centric blockchain alternative and their approach to infrastructure is similar to the nature-inspired actor-event foundations that Hugh speaks on.

Ugh, software development is getting so much more interesting!

[Moousaka]

Are there any articles or example code written about these "reduction trees"? Nothing shows up on my searches. Cheers!

[AdrianBoyko]

Most of the complexities in this discussion result from distributing actors across multiple machines on a network, which I guess is Akka’s thing (as well as Erlang’s). But if you’re trying to develop a program that will run efficiently on a single multicore machine, then something like Pony is much less convoluted and a better starting point to learn actor oriented programming.

[WillEhrendreich]

awesome episode, this was very informative and helpful. thanks!

[jakobbebop]

are the subtitles AI-generated? At 45:06 or so, they say "the item potency", which should be "idempotency"...

[ArunJayapal]

Does actor pattern make sense for a language like javascript/nodejs. Apart from the asynchronity the queues offer what else is there? Threads are out of the window. Love to hear some thoughts on this?

[stolenlaptop]

I always called this style of programming managers but have used it on occasion.

[aelon]

You might enjoy taking a dive into Temporal.

There are two things that stuck out to me from this conversation.

1. Emergence. I enjoyed emergence when dealing with AI in games. However in a business setting, more often than not you want to know that very specific outcomes will happen, even if eventually.

2. Designing state machines . With temporal you could start thinking about it replacing state machines. However state machines are not what we want to achieve, it's a tool to achieve it. With temporal you focus on what you want to achieve.

Let me know if you find this s interesting!

Cheers

[afailable]

Do you have to search the whole tree for a leaf that has given stock to the request id before you can continue with processing the request?

How do you guarantee idempotency without visiting all the leaves?

The trunk knows what the overall count is, but how do you verify the request isn't duplicate?