Which command file is crucial for defining build instructions in AWS CodeBuild?

The crucial command file for defining build instructions in AWS CodeBuild is the buildspec.yml file. This YAML file serves as a blueprint for the build process, detailing the steps and commands that CodeBuild should execute during various phases of the build lifecycle, such as install, pre_build, build, and post_build.

The buildspec.yml file allows developers to customize their build environments by specifying the necessary commands to install dependencies, run tests, and package applications. This flexibility is critical in enabling the efficient automation of various development practices like continuous integration and continuous deployment (CI/CD).

By utilizing a buildspec.yml file, users can ensure that their builds are consistent and reproducible, streamlining the development process significantly. The structure and syntax of the file are tightly integrated with the AWS CodeBuild service, making it an essential component for anyone looking to leverage AWS for building and sharing their applications.