How TikTok Efficiently Manages Its 200K-File Frontend Monorepo 🤔

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How TikTok Manages a 200K File Frontend Monorepo

In today's fast-paced software development world, managing a large-scale frontend application can be a challenging task, especially when you have millions of lines of code and multiple services to maintain. For companies like TikTok, managing such complexity requires efficient processes, tooling, and architectural strategies. One such strategy is the use of a monorepo.

In this blog post, let’s dive deep into what a monorepo is, its advantages and disadvantages, and how TikTok manages its massive 200K-file frontend monorepo using TypeScript. We'll also look at who else uses monorepos and how they can be beneficial for large-scale applications.

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What Is a Monorepo? 🤔

A monorepo, short for monolithic repository, is a version control strategy where multiple projects or services are stored in a single repository. Rather than separating each project or microservice into its own repository, a monorepo consolidates everything into one.

In simple terms, a monorepo houses all codebases—whether they’re related to frontend, backend, or shared libraries—under one roof. This makes it easier for teams to collaborate, manage dependencies, and maintain consistency across projects.

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Advantages of a Monorepo 🚀

1. Shared Code & Libraries 🔄: A monorepo makes it easy to share code across multiple projects. For example, a shared UI component library or utilities can be reused throughout different services without needing complex versioning.

2. Atomic Changes ⚡: A developer can make changes that span across different projects and services in a single commit, ensuring that everything stays in sync.

3. Consistency 🧑‍💻: All projects share the same versioning, tooling, and configurations, which can reduce the potential for mismatched dependencies.

4. Easier Refactoring 🔧: Since all projects are in one place, refactoring code (e.g., renaming a common method or changing an API) becomes a simpler task, impacting all necessary areas of the system at once.

5. Simplified Collaboration 🤝: Teams can work more closely together, view changes in real-time, and avoid issues arising from fragmented repositories.

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Disadvantages of a Monorepo ⚠️

1. Scalability Issues 📈: As the repository grows, managing thousands or even millions of lines of code can become challenging. Version control systems might struggle to keep up with the size.

2. Complex Build Systems 🛠️: A single repository can contain many different applications, which may require specialized tooling to ensure that only the impacted parts of the code are built or tested.

3. Build Time ⏳: In large monorepos, building everything at once can take a long time. Efficient build processes must be implemented to avoid delays.

4. CI/CD Overhead 🔄: With many services and projects in a monorepo, configuring Continuous Integration (CI) and Continuous Deployment (CD) pipelines can become more complex.

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Who Else Uses Monorepos? 🏢

Many top-tier companies use monorepos to manage their codebases. Here are a few examples:

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TikTok’s TypeScript Monorepo 🎵

Now, let’s focus on how TikTok specifically manages its 200K-file frontend monorepo, which primarily uses TypeScript.

Challenges Faced by TikTok 😰

Managing such a large monorepo comes with its own set of challenges, especially with 200,000 files. TikTok's engineering team needed to design efficient systems to handle the complexity:

1. Code Splitting 🔄: Not all services in a monorepo are related. TikTok uses advanced build tools like Bazel and Nx to split the code into meaningful chunks, which allows for more efficient builds and tests. This way, only the impacted areas are rebuilt or retested.

2. Fast and Scalable Builds ⚡: TikTok integrates TypeScript with Webpack and uses CI/CD pipelines with intelligent caching and parallel builds to ensure that development stays fast and scalable.

3. Type Safety 🔐: With TypeScript, TikTok ensures that their frontend code is highly type-safe. This prevents a lot of runtime issues that might arise when working with complex codebases.

4. Tooling and Automation 🤖: TikTok uses powerful tooling and custom scripts to automatically handle tasks like dependency management, versioning, and testing. This helps developers focus on writing code without worrying about the intricacies of the build process.

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Code Snippets 🔧

Here’s a simplified example of how TikTok might configure its TypeScript monorepo using Bazel to optimize builds:

Bazel Build Configuration:

# BUILD.bazel
load("@npm//typescript:index.bzl", "ts_library")

ts_library(
    name = "app",
    srcs = glob(["src/**/*.ts"]),
    deps = [
        "@npm//lodash",
    ],
)

This snippet sets up a TypeScript build rule for a specific app in the monorepo, helping to organize and manage frontend dependencies efficiently.

Nx Workspace Configuration:

{
  "npmScope": "tiktok",
  "projects": {
    "ui-library": {
      "tags": []
    },
    "app": {
      "tags": []
    }
  }
}

Here, Nx helps manage and coordinate multiple apps and libraries in the monorepo, making it easy to share components like the UI Library across different applications.

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Case Study: A Day in the Life of TikTok’s Dev Team 📅

Let’s look at how TikTok’s development team uses their monorepo in action:

Scenario: The team needs to make a change to a shared UI component used across multiple applications.

1. A developer checks out the monorepo and identifies the component that needs updating.

2. Using Bazel, only the impacted areas of the code are rebuilt, and the build process is fast.

3. The developer adds new features to the UI component and runs tests using Jest and Cypress (integrated into the CI pipeline) to ensure everything works.

4. The developer pushes the changes, and the CI/CD pipeline automatically deploys them to the staging environment.

5. Once the code passes QA, it’s deployed to production with minimal downtime.

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Resources for Further Study 📚

1. Monorepos in the Real World - A comprehensive guide on how major companies use monorepos: Monorepo Guide

2. Bazel Documentation - Learn how to use Bazel for efficient builds in a monorepo: Bazel Documentation

3. Nx Documentation - Explore Nx, a powerful set of tools for managing monorepos: Nx Docs

4. TypeScript Handbook - Get familiar with TypeScript to understand how TikTok manages type safety: TypeScript Handbook

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Conclusion 🎯

Monorepos have become a powerful tool for managing large-scale applications, especially for companies like TikTok, which manages a 200K-file frontend monorepo. By using TypeScript, Bazel, and Nx, TikTok can maintain a highly scalable and efficient development process. While monorepos offer numerous benefits—such as code sharing, atomic changes, and collaboration—they also come with challenges that require careful consideration of tooling and build processes.

Whether you're working at a small startup or a large tech giant, understanding how to manage a monorepo could be a game-changer for your development workflow. 🚀

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This article explores TikTok's management of a massive 200,000-file frontend monorepo using TypeScript. It highlights the advantages and disadvantages of monorepos, such as shared code, atomic changes, and scalability issues. The piece also discusses strategies TikTok employs, including code splitting with Bazel and Nx, fast builds with Webpack and CI/CD pipelines, and ensuring type safety with TypeScript. The article provides insights into how other companies like Google, Facebook, and Uber use monorepos, offering resources for further study and understanding of this powerful tool for large-scale application development.