Event driven microservices

I’ve got lucky I got my spot in last London GOTO conference. Theme was obviously event driven microservices and how they simplify whole architecture of complex applications. After 2 days of listening about them there was no other choice than prototype.

Most intriguing for me was the idea of performing read through event bus as well as writes. It kinda hit me as being against CQS. Couldn’t get why and how. Being in mindset of transactional storage wasn’t helping as well :P

Building event driven microservices

Requirement as simple. One service is providing data and other is requesting and processing it. And some interface to interact with. No need for web, as it’s prototype/proof of concept. Console app it is and Symofny as framework of choice as the simplest way to scaffold code. Yesterday I was thinking about getting kafka but again, I wanted to see results not caring much about technology.

If you want to do system like that in real life please don’t use PHP for that :D

Code you will find here.

So how it works?

I’ve got positively surprised by the effect. Everything was obviously done under a second. Even checking on microsecond level shown loads of time saved in comparison to HTTP.

Think this way – sending order and getting item gives you 2 HTTP calls. It’s not much but with more services interested in this topic it will only grow. And all of it will be done during main order request. So user facing system will be slowed down by every new service attached. Even if response time is about 50ms with only 4 of them it adds 200ms on top of all other processing.

When your microservices communicates with each other with events you’re getting at least three advantages I can think of right now:

  1. No HTTP, less network connections means less time wasted on the wire
  2. Events are asynchronous so if your critical path is finished you can inform end user about it without waiting for all the rest to finish
  3. If one of services in chain fails events will stay in the infrastructure. You’re not loosing any data.  Rest of system is working as normal. Error is atomic to one place. And after it’s fixed you can start processing messages from where it stopped.

Last point is illustrated in my example. When you request non existent item ItemService will fail. Fix collection adding new index and rerun it. Boom. Order gets processed like nothing happened. Just with a bit of delay.

Conclusion

If you can use this pattern it will give you a lot of freedom. Communicating with event bus of any sort will save you a lot of time and money. One thing to do is just to convince your team and company it’s the right thing to do. But it’s topic for another post ;)

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