Optimize Bazel Builds for Large Monorepos

Production patterns for Bazel in large-scale monorepos, covering workspace architecture, remote caching and execution, build performance optimization, custom Bazel rules, build debugging, and Bazel migration. Core concepts: Targets (buildable units), Packages (directories with a BUILD file), Labels (//path/to:target), Rules (how to build a target), and Aspects (cross-cutting build behavior).

Use this when setting up Bazel for a monorepo, configuring remote caching or execution, optimizing build times, writing custom Bazel rules, debugging build issues, or migrating an existing build to Bazel.

Not needed for small single-language projects where a simpler build tool is sufficient, or for tasks unrelated to Bazel build optimization.

Provides seven ready-to-adapt templates: a WORKSPACE.bazel configuration registering JS/TS (aspect_rules_js, a Node toolchain, npm_translate_lock) and Python (rules_python) dependencies; a .bazelrc covering performance flags like --jobs=auto and CPU/RAM resource limits, disk and repository caching, optional remote caching and remote execution configs, platform-specific and CI build configurations, and test/coverage settings; TypeScript and Python library BUILD.bazel files (ts_project/js_library/jest_test, and py_library/py_test/py_binary with pip requirements); a custom Bazel rule implementing a docker_image build action; bazel query patterns for dependency analysis - deps, reverse deps, changed-targets-since-commit, dependency graph generation, tag-based filtering; and a remote-execution platform and toolchain configuration, including exec_properties for a Docker-based worker container and a Linux/x86_64 cc_toolchain definition. The custom Docker rule's implementation declares a .tar output file, assembles dockerfile/base-image/layer arguments, and runs a builder executable via ctx.actions.run, returning a DefaultInfo provider with the built image.

### Find all dependencies of a target
bazel query "deps(//apps/web:web)"

### Find reverse dependencies (what depends on this)
bazel query "rdeps(//..., //libs/utils:utils)"

Performance-optimization commands profile builds (--profile=profile.json plus bazel analyze-profile), identify slow actions (--execution_log_json_file), profile memory (--memory_profile), and skip the analysis cache when needed. Best practices: use fine-grained targets for better caching, pin dependencies for reproducible builds, enable remote caching to share artifacts, use visibility deliberately to enforce architecture boundaries, and write one BUILD file per directory. Anti-patterns to avoid: using glob for dependencies instead of explicit lists, committing bazel-* output directories, skipping WORKSPACE setup, and ignoring build warnings. References Bazel's own documentation, its remote-execution docs, and the rules_js project.

Build and platform engineers setting up, optimizing, or migrating a large monorepo's Bazel build, who need concrete, copy-adaptable WORKSPACE, BUILD, and .bazelrc templates and query patterns rather than generic Bazel concepts explained from first principles.