[trb]

I've experienced both, and I prefer the mono repo.

Our challenges with multiple repos mostly revolved around builds and orchestration. We had to apply all build/deploy changes to all repos, and that increased the chance of doing some small thing wrong. Finding what exactly is wrong with one repo that should be the same as all the others was like one of those "find the differences" pictures. Really annoying.

This is more microservices than multi repo related, but making sure all the different services are released in sync was hard and annoying and often caused issues. Eg a specific API was updated and released but the for a consumer had to be rolled back and the rolled back version wasn't compatible with the new API. So current version and roll back wasnt an option. Rolling back the API would require rolling back all consumers but crap, one of the consumers applied a big migration to our core database and rolling that bank would take forever. And so on.

Just tons of little edge cases that went wrong at the worst time because it was so hard to foresee all the issues.

Monorepo and monolith is so comfy. Want to share code? Move it up one or two directories and import from there. No issues with two bundled react versions in two builds. Easy to refer to code from other teams, never an issue that someone forgot to add you to that one repo almost no one uses but that you need to commit to during firefighting.

I'm not saying multi repos/micro services can't work, but it's hard - you need strong processes that prevent people from being lazy, you need monitoring and management well defined, you need extra tooling that's aware of the repo structure, you need a strong story around migrations, and so much more.

I currently work with a mono repo monolith that over a thousand devs contribute to daily and it's Cindy comfy. It feels much easier to fix too many devs in one repo (primarily via strong compartmentalization) than to fix too many repos/services