One of the main benefits of decoupling a monolithic application is getting the freedom to release, scale and manage different components separately. Each team becomes empowered to define their own practices, procedures and policies that are appropriate to their business requirements.
Have a mission-critical component that needs 5 9s reliability (auth or billing)? Great, release that carefully over multiple days with canarying across failure zones. Working on an experimental API for a new mobile app? Awesome, ship every commit.
The common quote "if you have four groups working on a compiler, you’ll get a four-pass compiler" clearly has architecture following from organizational structure.
I think your original comment was unclear, if not misstated. I had read the "like" in "[a]rchitect your microservices like your org chart" as something like "to resemble", and the rest of the comment seems to follow just fine. Other readings seem possible but I don't see one that gives the sense you want without what feels like some serious contortion.
In any case, no worries, we're clearly on the same page now - just trying to figure out what went wrong.
Similarly, if you run a website that does batch processing of images for example, the image processor application would be a microservice since that would scale independent of website load. It could be that you would need to process 100 or even 1000 images for each user, on average, and it doesn't make sense to scale your whole application when a bulk of the application processing is for image processing.
When deployment and coordination become an issue, that is when _deployment_ needs to get split up. But given our current RPC mechanisms, deployment and invocation are over-coupled so we have to consciously make these decisions when they could be made by the runtime.
In either case, the best time to do it would be when you feel the increased speed and agility is outweighed by the added overhead. The speed and agility comes from small teams being able to operate mostly independently.
There are of course a ton of exceptions to this. For example, if you're using AWS Lambda or Google cloud functions, they do a lot of that 25% for you, as long as you're willing to do it their way, so now you have an incentive to go microservices sooner. Also, going microservices will probably allow you to scale up faster if you've done it right. So if you expect a huge spike in traffic, that's a good time to go microservices.
There is lots of good material on the pros and cons of microservices, but when to actually make the switch, or if you should start out at microservices, is a very situation specific question and relies on a lot of external factors.
The best I can say is look at the pros and cons and figure out what that costs or gains you in your particular situation.
I would say, don't use Microservices unless you have 100 or more employees.
You will learn about how to model complex domain models and how to decompose them into Aggregate's. The Aggregate is the key to where to create new microservices, as each aggregate should only contain domain objects that relate to itself.
Payments is a great example of an Aggregate.
#anecdata
The other heuristic to follow is how your company is organized. If you have a separate team working on a major feature then perhaps that could be its own service so they can own the full-stack.
Otherwise, stick to the monolith for the best results.
- independent deployment of this service
- independent scaling of this service
- independent implementation stack for this service
- security - minimize privilege escalation and access to infrastructure
- scalability - different workloads need different metrics to scale(CPU bounds vs connection bound)
- dependencies - why burden devs with all dependencies especially some that are more difficult to setup dev environments for
- service per backend dbs/etc (overlaps with the above)
- domain - can place domain specific skills on a team