alt Hacker News> If you communicate with one another you are serializing and deserializing a shared type.
Yes, this is absolutely correct. The objects you send over the wire are part of an API which forms a contract the server implementing the API is expected to provide. If the API changes in a way which is backwards compatible, this will break things.
> That shared type will break at the communication channels if you do not simultaneously deploy the two services.
This is only true if you change the shared type in a way which is not backwards compatible. One of the major tenets of services is that you must not introduce backwards incompatible changes. If you want to make a fundamental change, the process isn't "change APIv1 to APIv2", it's "deploy APIv2 alongside APIv1, mark APIv1 as deprecated, migrate clients to APIv2, remove APIv1 when there's no usage."
This may seem arduous, but the reality is that most monoliths already deal with this limitation! Don't believe me? Think about a typical n-tier architecture with a backend that talks to a database; how do you do a naive, simple rename of a database column in e.g. MySQL in a zero-downtime manner? You can't. You need to have some strategy for dealing with the backwards incompatibility which exists when your code and your database do not match. The strategy might be a simple add new column->migrate code->remove old column, including some thought on how to deal with data added in the interim. It might be to use views. It might be some insane strategy of duplicating the full stack, using change data capture to catch changes and flipping a switch.[0] It doesn't really matter, the point is that even within a monolith, you have two separate services, a database and a backend server, and you cannot deploy them truly simultaneously, so you need to have some strategy for dealing with that; or more generally, you need to be conscious of breaking API changes, in exactly the same way you would with independent services.
> The logical outcome of this is virtually identical to a distributed monolith.
Having seen the logical outcome of this at AWS, Hootsuite, Splunk, among others: no this isn't true at all really. e.g. The RDS team operated services independently of the EC2 team, despite calling out to EC2 in the backend; in no way was it a distributed monolith.
[0] I have seen this done. It was as crazy as it sounds.
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>This is only true if you change the shared type in a way which is not backwards compatible. One of the major tenets of services is that you must not introduce backwards incompatible changes. If you want to make a fundamental change, the process isn't "change APIv1 to APIv2", it's "deploy APIv2 alongside APIv1, mark APIv1 as deprecated, migrate clients to APIv2, remove APIv1 when there's no usage."
Agreed and this is a negative. Backwards compatibility is a restriction made to deal with something fundamentally broken.
Additionally eventually in any system of services you will have to make a breaking change. Backwards compatibility is a behavioral comping mechanism to deal with a fundamental issue of microservices.
>This may seem arduous, but the reality is that most monoliths already deal with this limitation! Don't believe me? Think about a typical n-tier architecture with a backend that talks to a database; how do you do a naive, simple rename of a database column in e.g. MySQL in a zero-downtime manner? You can't. You need to have some strategy for dealing with the backwards incompatibility.
I believe you and am already aware. It's a limitation that exists intrinsically so it exists because you have No choice. A database and a monolith needs to exist as separate services. The thing I'm addressing here is the microservices and monolith debate. If you choose microservices, you are CHOOSING for this additional problem to exist. If you choose monolith, then within that monolith you are CHOOSING for those problems to not exist.
I am saying regardless of the other issues with either architecture, this one is an invariant in the sense that for this specific thing, monolith is categorically better.
>Having seen the logical outcome of this at AWS, Hootsuite, Splunk, among others: no this isn't true at all really. e.g. The RDS team operated services independently of the EC2 team, despite calling out to EC2 in the backend; in no way was it a distributed monolith.
No you're categorically wrong. If they did this in ANY of the companies you worked at then they are Living with this issue. What I'm saying here isn't an opinion. It is a theorem based consequence that will occur IF all the axioms are satisfied: namely >2 services that communicate with each other and ARE not deployed simultaneously. This is logic.
The only way errors or issues never happened with any of the teams you worked with is if the services they were building NEVER needed to make a breaking change to the communication channel, or they never needed to communicate. Neither of these scenarios is practical.
Managing two services is very different than managing 140. And databases have a lot of tooling, support, and documentation around migrations.