I don't really understand. If I have a database, and a service is talking to it, it can open a transaction. If I then want to talk to other services, and rollback that transaction based on what happens with those, I can do that.
Microservices changes nothing about this. If you want to remove transactions by splitting up your logic such that it operates in terms of sequences or something, you can do that, but that's just a choice like any other.
Well... don't do that? This is where microservices comes in. In a SOA architecture nothing really tells you when it's a good idea to split things up. Microservices is a methodology to help you avoid this exact situation.
You'd have the same problem in a monolith if you have two different modules working on the same db.
Assume you have two tables A and B on the same DB. They are sort of seen as unrelated. Suddenly a feature request requires that A and B are mutated together consistently.
If it is in one service you just use a common DB transaction and get it done.
If it is in one microservice for A and one microservice for B then you have to somehow implement this transaction yourself. This is possible but more work.
OK imagine that you have two different modules that manage transactions to a database. Now suddenly you need there to be consistent mutations between those functions.
Do you see my point? Microservices do nothing here - you have run into antipatterns that are universal, and that microservice architecture addresses explicitly as an antipattern.
I do not see your point. Sometimes consistent mutations between modules is wanted. Monoliths lets you do it. Perhaps you discovered your module boundaries were wrong, you create a supermodule to encaspulate both to coordinate the joint transaction and then split up later a different way and so on.
Module boundaries are refactorable.
Importantly, what if the alternatives you end up with achieve the same things with microservices end up causing a ball of mud of services, reimplementing transaction logic that belong in your DB in your homegrown network protocols?
You seem to say that some things are not possible with microservices and therefore this leads to cleaner code. My retort is that the kind of things one sometimes come up with as workarounds to make things still work for microservices are so complex that the cure is worse than the disease you wanted to cure in the first place.
Why are microservices not refactorable? This is the same exact issue in both cases. You designed something for a use case, the use case changed, now your old design isn't working. So maybe you merge those two services, or merge those two modules, or whatever else you want to do.
> reimplementing transaction logic that belong in your DB in your homegrown network protocols
Don't do that? I mean, again, this issue of "I wrote something the wrong way and now I have to fix that" is not any better or worse in microservices.
> My retort is that the kind of things one sometimes come up with as workarounds to make things still work for microservices
That doesn't sound like microservices. In fact, even the idea of having a database shared across services doesn't sound like microservices - it's an explicit antipattern. So it sounds like a bad SOA design. The point of microservices is to take SOA and add patterns and guidance to avoid the issues you're talking about.
Microservices gets owned by different teams, teams get cemented, politics get in the way of refactoring. Game over.
Sure, if you are a single team working on 10 microservices you can probably refactor with abandon without spending 70% of your working days in meetings talking about migrations and trying to sync strategies...
You may have experiences that that microservices are as easy to refactor as monoliths; in my experience it is orders of magnitude harder...
I think there is a bit of a "No true scotsman" fallacy at play here. You see something you do not like then it is "not microservices done properly".
How about state all the things you don't like about monoliths , then I say "that is not monoliths done properly", "don't do that" for each one?
I think both monoliths and microservices can lead to good code or balls of mud depending on the organization and developers involved.
Real question isn't whether "microservices done right" is better. The question is: does a Decision to do microservices reduce the chances of a ball of mud, when that Decision is then implemented by imperfect developers in an imperfect organization?
PS I always meant that each microservice had their own DB above, we agree on that and I never dreamt otherwise.
What I was getting at is that when you go distributed, sometimes quite complex patterns must be applied to compensate.
You may say the architecture is then "better", but on what metric? It is certainly more work up front -- so you start out in the negative and to become better the system and organization need at least to get to a certain scale, you need to save in the hours you invested to come out ahead.
In many scenarios the cost in developer-months needed up front is just as important as other factors in evaluating the best architecture. E.g. a scrappy startup simply should not do it IMO. Corporations..... perhaps;but I have seen it gone badly. (I guess it is just not "done right" then? See above.)
PS I think microservices excel in making people FEEL productive (doing work that is not directly benefiting the company).
I have personal experience with the same product built twice, once as a monolith by a small team that worked really well and once as lots of services.
The featureset and development speed is about the same, but the many-services requires 10x as many people.
However by splitting into many services everyone feels productive doing auxiliary and incidental work. Only those of us who worked on the first system are able to see that the total output of the company is the same but 10x as expensive.
> Microservices gets owned by different teams, teams get cemented, politics get in the way of refactoring. Game over.
I don't understand how microservices make this worse in any way. Modules get owned by different teams all the time.
> You may have experiences that that microservices are as easy to refactor as monoliths; in my experience it is orders of magnitude harder...
Yes, I have said before that I believe merging is fundamentally simpler than splitting. If we're just talking about merging a module vs a service, I don't believe either is harder than the other - I mean... nothing about microservices prevents you from using modules, and indeed I would highly recommend it.
> I think there is a bit of a "No true scotsman" fallacy at play here. You see something you do not like then it is "not microservices done properly".
For sure, and that's a failing of microservices. People think microservices means "SOA", or "write a lot of services". If you want to criticize SOA or whatever, sure, the argument of "don't do that" goes away.
> How about state all the things you don't like about monoliths , then I say "that is not monoliths done properly", "don't do that" for each one?
I probably could state a bunch of things that are pretty fundamental, but I don't think it's important - I don't know that I've actually said anywhere that microservices are better than monoliths, what I've instead said are the benefits of microservices that I see, which others have taken to mean that I somehow think monoliths or modules are bad.
> You may say the architecture is then "better"
I honestly don't think I've said that anywhere, or even made a judgment anywhere.
I think I can summarize, again, what I've said.
1. Network boundaries provide a physical layer that enforces isolation of state and the use of message passing
2. Isolation of state makes scaling a system easier
3. Isolation of capabilities makes securing a system easier
4. SOA inherently leverages the network boundary
5. Microservice Architecture is similar to SOA but with a bunch of patterns, guidance, and concepts that you leverage in your design
What I've received in response is a hodgepodge of:
1. "Modules can isolate state" - only true in some languages, and even then there's no physical barrier enforcing it, you're relying on developers to maintain that isolation.
2. "But what if you do anti-patterns that microservices tell you not to" - ok, that's why microservice architecture has books and documentation about what not to do. If you do those things, I'm not going to blame you, it's a failing of all methodologies when users have a hard time understanding them.
But so far the anti-patterns mentioned aren't really compelling or specific to microservices. You wrote code to satisfy a domain, the domain changed, now you need to change that code so that it satisfies the new domain. That happens all the time, merging services isn't any harder than merging modules.
3. General misunderstandings about state, security, etc.
> What I was getting at is that when you go distributed,
I'm not really convinced that "distributed" is the right word here. People talk about distributed systems being complex, and I think they're confused - what's complex is consensus, but splitting one service from another service shouldn't impact consensus, and the fact that they're now located on two different assets does not necessarily make things more complex.
Those services may be more complex, if your application was quite trivial - a totally stateless system with no external connections, for example. I see no reason to rewrite 'grep' as a microservice, and I would never recommend that.
Those services may now be more error-prone because you have things like dns, tcp, etc involved. If you don't want to make that tradeoff, that's OK, you could be right in that case. Again, no need to make all software be microservices.
(Going to respond to your other message here)
> PS I think microservices excel in making people FEEL productive (doing work that is not directly benefiting the company).
Maybe, I don't really know. It isn't my experience, but that's just me. Most developers seem to be pretty bad at their jobs so I imagine that all sorts of issues can be experienced. Certainly the idea of rewriting a monolith as a microservice seems like a red flag unless there were very specific needs.
Microservices changes nothing about this. If you want to remove transactions by splitting up your logic such that it operates in terms of sequences or something, you can do that, but that's just a choice like any other.