In the world of software development, monorepo setups have become a popular trend, especially with tools like Nx that promise better integration, faster builds, and more efficient workflows. A monorepo is where multiple projects, often microservices or libraries, live in a single repository. Sounds convenient, right? One repo to rule them all! But not so fast — while the monorepo approach might shine in some cases, it’s not always the best solution, especially when performance is a key concern.
Let's dive into some of the key performance issues with monorepo projects, and why Nx, despite its benefits, may not always be the silver bullet.
Longer Build Times for Large Projects
Monorepos are supposed to streamline things by centralizing code, but as the number of projects grows, so do build times. Even though Nx is optimized to run tasks efficiently, a monorepo with hundreds of libraries or services means that dependency graphs can get extremely large. When a change is made, Nx needs to analyze dependencies and determine what needs to be rebuilt. In some cases, this process can get complex and slow.
Imagine that a tiny bug fix in a small library requires building a significant portion of the repo. This overhead can result in frustratingly long build times, killing developer productivity and increasing CI pipeline duration. In contrast, a polyrepo approach (where each project lives in its own repository) may allow independent builds, reducing the scope of what needs to be compiled and tested.
Overhead with Task Scheduling
Nx introduces task scheduling to optimize parallel builds and test runs. However, this scheduling system adds a layer of complexity. As the number of developers and commits grows, task execution can become bottlenecked. Nx does a good job of managing this, but in large monorepos, the overhead of orchestrating hundreds or thousands of tasks becomes inefficient.
Moreover, Nx’s caching mechanism, designed to speed up builds by reusing previous results, can sometimes lead to cache misses due to small changes, forcing a rebuild of many unrelated parts of the repo. This negates the caching benefits and causes slowdowns, which can be especially problematic in CI environments where time is crucial.
Dependency Bloat and Codebase Size
don’t actually need for a specific service or library but are kept for “convenience.” This leads to increased disk usage, slower git operations, and more complicated dependency management.
Over time, this leads to situations where developers are dealing with dependency hell. Updating shared libraries or dependencies becomes a monumental task, as every project in the monorepo must be considered. This can create a ripple effect, leading to longer build times, merge conflicts, and higher risk of bugs.
Scaling Development Teams
In smaller teams or projects, a monorepo with Nx might work fine. But as your team scales, so do the issues. With a monorepo, you are essentially coupling everything together. Even though teams may work on different parts of the codebase, they are still impacted by changes in other parts of the repo. This increases the coordination overhead, slowing down development and causing friction between teams.
A polyrepo setup allows teams to work more independently, with fewer merge conflicts and less coordination. When you have multiple teams contributing to a single monorepo, the velocity of development can decrease due to these conflicts, hurting overall productivity.
CI/CD Pipeline Bottlenecks
CI/CD pipelines in monorepos can become a nightmare. Despite Nx’s ability to run only affected projects, changes in shared libraries or configurations can still trigger the build and test of a large number of projects. The more services or libraries you have in a single repo, the more your pipeline becomes clogged with tasks. Nx’s distributed caching can help alleviate some of this, but it's not a perfect solution, especially in a fast-paced environment where small changes can trigger large rebuilds.
In contrast, in a polyrepo setup, the CI/CD pipeline can be much more granular, running builds and tests only for the specific project where the changes were made. This localized pipeline approach can result in faster deployments and quicker feedback.
Conclusion: Is Nx Always the Best Solution?
While Nx and the monorepo approach offer some significant benefits, such as code sharing and streamlined tooling, they can introduce serious performance bottlenecks for large, complex codebases. Build times, task scheduling overhead, dependency bloat, and scaling issues are all valid reasons why monorepos might not be the best fit in certain scenarios.
For smaller projects, or tightly integrated systems, a monorepo can be highly effective. But as your codebase and teams grow, you might find that the performance penalties outweigh the benefits. In those cases, it’s worth considering a polyrepo setup, or at least weighing the trade-offs before fully committing to Nx and monorepos.
Ultimately, the right approach depends on the size of your project, team structure, and performance needs. Monorepos aren’t a one-size-fits-all solution — and sometimes, they suck.
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