Bazel vs Docker: What are the differences?

Introduction:

Bazel and Docker are both powerful tools used in software development and deployment. However, they have key differences in their functionalities and purposes. In this article, we will explore the differences between Bazel and Docker in detail.

1. Build Process: Bazel is primarily a build automation tool that focuses on creating reproducible and efficient builds. It uses a build graph to determine the dependencies and parallelizes the build process. On the other hand, Docker is a platform that allows developers to package their applications and dependencies into portable containers.

2. Isolation: Bazel provides isolation at a fine-grained level by implementing sandboxing techniques. It ensures that the build process does not have any external dependencies or side effects. Docker, on the other hand, provides a more heavyweight form of isolation by using containerization. It encapsulates an entire environment, including the application and its dependencies.

3. Portability: Bazel is designed to be highly portable and platform-agnostic. It can build software for various platforms and architectures without any modifications to the build configuration. Docker, on the other hand, provides a consistent execution environment by abstracting away the underlying operating system and hardware, making it easier to run applications across different platforms.

4. Reproducibility: Bazel emphasizes reproducibility by ensuring that the build process is hermetic and deterministic. It uses content hashing to verify that the build inputs are unchanged and produces the same outputs consistently. Docker focuses more on providing a consistent runtime environment, but it may not guarantee the exact same outputs for a given input in different environments.

5. Dependency Management: Bazel has sophisticated dependency management capabilities built-in. It can resolve and fetch dependencies from various sources efficiently, allowing for incremental builds. Docker, on the other hand, relies on package managers and container registries to manage dependencies within containers.

6. Resource Utilization: Bazel optimizes resource utilization by caching build artifacts and only rebuilding what is necessary. It can skip the build process for unchanged dependencies, resulting in faster build times. Docker, however, may require building the entire container from scratch whenever there is a change, leading to potentially longer build times.

In summary, Bazel focuses on efficient and reproducible builds with fine-grained isolation and dependency management, while Docker provides encapsulation of applications and their dependencies for easy deployment and portability.