Comment by majormajor | Hacker News Reader

Comment by majormajor | Hacker News Reader

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When I've used a monorepo, that was one of the explicit goals.

Avoiding "here's my new library version, go see if it breaks your shit" was the goal - you make a change, you run the tests, you see if the whole company's code can still build or not. Having fully-separate projects in directories in the monorepo using published dependencies was considered an antipattern (though it was very hard to keep some teams from doing that).

The disadvantages of the resulting monorepo weren't "this directories are so big to keep checked out when I'm just working on one specific project" it was "our old build times and build tools are dying under the strain and even trying to move to a 'monorepo friendly' build tool might be an intractable problem because our dependency graph has become such a mess of spaghetti."

A monorepo that was done well from the start so you don't have the slow-spaghetti-build problem from months or years of "oh it's easy to depend directly on this full other module, let's just do that" sounds very appealing. We just didn't pull it off in practice, and this project would ... maybe... help in the early stages by letting people have more restricted checkouts? But only if you already know what you're doing anyway.

You seem to mix two different goals here. Atomic commits across everything surely is a feature of a monorepo which a manyrepo setup cannot replicate. However, the "test whole company's code" could also be achieve with a central package manager and many repos. That is what Amazon does: http://beza1e1.tuxen.de/amazon_manyrepo_builds.html

Yeah, there's two different aspects in there (though without the full-blown testing making broad atomic commits isn't super attractive to me anyway. ;) )

Amazon's Brazil system doesn't sound like it does the "test the whole company's code" aspect in the same way.

> If you create a package at Amazon, you specify an interface version like "1.1". As long as changes are backwards-compatible, the interface version is not changed. When Brazil builds a package, it appends an additional number to turn it into a build version like "1.1.3847523". You can only specify dependencies on interface versions.

So if I'm working on a non-backwards-compatible version, my users aren't going to pull it down immediately in the build (if I properly call it version 1.2.x), so the build won't show which of them it broke.

Even if you depend on the latest version instead of pinning to a major version, how would I force a company-wide build of everything that depended on me using my not-yet-landed branch? I can run those tests in a monorepo on my branch directly, I don't see how I'd do it in a manyrepo setup without a very specific set of "every project in the company specifies its dependencies as depending on specific, easily-overrideable, commit SHA versions."

Actually to do that, one was is to just make 1.1 as 1.0 in a test branch to do the test build and build it against everything. There are other ways to do this as well, depends on what you're doing.

But it's important to note amazon doesn't monorepo like you are used to thinking, so it is actually on everyone to take the updates on the schedule they've set via automation or if it's an emergency via ticketing / policy. You are merely seeing if it's going to work, the automation does the rest, possibly over weeks.

And I am simplifying things here to make it easier to understand. Understanding brazil from not using it, is about as difficult as understanding git rebase coming from CVS, eg there are concepts you didn't even knew existed that you have to understand how to use to operate at large scale.

The basic problem with trying to solve the problems with versioned releases with monorepos is that the code in the repo and the code in production are not the same. If you change your service’s API, just updating all of the other clients of your service in the repo is not sufficient to skirt the problem of different clients expecting different APIs.

Re the tooling issue, I’ve frankly never seen it solved. I presume Google’s done it, because they’re a bit messianic about the whole thing, but outside of them, I suspect all monorepo implementations fit into the “Communism” model of working great in theory.

> If you change your service’s API, just updating all of the other clients of your service in the repo is not sufficient to skirt the problem of different clients expecting different APIs.

Most Google APIs are written in protobuf, which is backwards compatible over the wire. This makes most changes painless, although caveat emptor as things can still get messy as they do in the real world. With something like a Java interface, it doesn't really matter if those APIs change because all the code is built and released together at HEAD.

Backwards compatible from a parsing-this-message-won't-blow-up standpoint but not necessarily from a semantic meaning-of-each-field standpoint if your devs are ... clever ... enough. ;)

That discipline to commit to an API and meaning for each field and not keep tinkering with it in messy ways is an under-valued and under-evangelized aspect.

> With something like a Java interface, it doesn't really matter if those APIs change because all the code is built and released together at HEAD.

Right, this is the thing that winds up following from the monorepo - the monorepo problem goes away if we just release everything, the whole fuckin’ system, into production every time we make any update to master. If that’s your system, hats off to you, I’m not nearly that good of an engineer.

It's actually easier, in many ways -- if you can manage to release continuously. It forces you to stage your code incrementally and you should be able to roll back things easily if you see breakage.

If your services are backwards compatible to talk to each other, then you don't need to release instantly. Making breaking changes is tricky, but you don't need to release everything.

I don't understand the problem. Code structure that listens to dev/prod mode can handle the different APIs. Branches to mark prod vs. dev.

Can you give a more concrete example of the problem? I don't think I'm understanding.

The pitch I often hear with monorepos is “When you change your service/library/whatever, you can simultaneously change all of the clients of that library/service/whatever in one PR”. The problem is a PR is not a release - just because the code in the repo is up to date doesn’t mean the code in production is. So, for example, if your service changes to require an extra parameter in the API, sure, you can update all of the clients of that API to provide that extra parameter, but that still requires them to be built & released as well - just updating the code doesn’t actually fix the deploy/release coordination problem.

Short version, you’re right, coordinating releases with feature flags, branches, etc. solves this problem, but it solves the problem in a multi-repo world too, and a monorepo doesn’t obviate the need for those solutions as many of its proponents seem to suggest.

There are probably legitimate uses for monorepos, but an awful lot of people seem to position them as a silver bullet that lets developers stop having to worry about coordination in a multi-service world, and that’s just not how it works out.

I agree that it doesn't improve things at the service interface level. What I have found is that I often have several internal libraries, and a monorepo ensures that I know if a change to my library breaks another service because they're all in one build. Keeping things consistent across services is very useful in my experience.

The issue comes if you are communicating between different binaries (for example, RPC requests or message handlers). Just because you can change the code atomically doesn't mean you can deploy the client and server atomically.

As someone pointed out though, proto mitigates a lot of this.

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