Message Broker: Goals and (De)Motivations

Recently, I read a twitter rant that described message brokers as poor combination load balancer, database, and service discovery tools. It hit me hard since I’d just spent a week diving into writing my own message broker. While I had my dislikes of brokers, I think they are handy tools. The tweeter stated that many of these things should be built into the services. The goal of which to keep the heavy work out of the center of the system. Message brokers doing the opposite when used as a central bus.

Having this description of the problem space is turning out to be nice. It gives me some different framing for the various parts of the message broker I’ll be building and the underlying needs. It also pointed out a heavy flaw that message brokers as a central bus can cause trouble in some systems. While that twitter rant dismayed me at first, I now feel even more energized in building this tool.

This framing of load balancer, database, and service discovery reminds me to go read up on that tech as well. Sourcing papers for those problems while looking into queuing related things. I can acknowledge and make sure these subproblems get solved well enough for my intended scale. That will be a key part of my design going forward, keeping my decisions favoring small to medium scale. I’ve seen message brokers work well in those scenarios and want to make an even better one of those.

This doesn’t mean one couldn’t use the broker in a larger scale operation. But, I’m architecting it to encourage deliberate clustering beyond medium scale. Clustering acknowledges the fact that there are usually groups of services that are able to meet a work request without speaking outside of their group except for one or two edges. What I hope to discover as part of the development process is how to encourage this. Whether documenting and creating examples will be enough, or if I’ll need more core features.

I think keeping the message broker light weight will be instrumental in encouraging clustering. If the message broker is heavy, folks wouldn’t want to run too many instances. If it requires a lot of tuning to be useful, folks will want to only tune it once as a central bus. Side note: as I typed this I realized this is why Redis is so good.

Among the lofty design and architecture goals I want to mention my motivations and put the goals in perspective. This project’s main goal is to be a learning project. I want to better understand the internals of message buses. Most green field backend projects will be utilizing a message bus and smaller services. Understanding the internals of the message bus and keeping them in mind will let me design better services.

I also want to build a complex, performance focused, realistic piece of software in Rust. I find the language fun to work with and writing my own thread orchestration that is safe is delightful. As I build up the basics in the broker and client, I’m learning a lot of practical Rust skills. Like many others writing and coding in Rust in their free time, I’m hoping this will help encourage more jobs writing Rust. If I’m lucky enough, I’ll get to secure one of those jobs.

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