Bazel Build Optimization

Bazel Build Optimization

Production patterns for Bazel in large-scale monorepos.

Do not use this skill when

• The task is unrelated to bazel build optimization
• You need a different domain or tool outside this scope

Instructions

• Clarify goals, constraints, and required inputs.
• Apply relevant best practices and validate outcomes.
• Provide actionable steps and verification.
• If detailed examples are required, open resources/implementation-playbook.md.

Use this skill when

• Setting up Bazel for monorepos
• Configuring remote caching/execution
• Optimizing build times
• Writing custom Bazel rules
• Debugging build issues
• Migrating to Bazel

Core Concepts

1. Bazel Architecture

workspace/
├── WORKSPACE.bazel       # External dependencies
├── .bazelrc              # Build configurations
├── .bazelversion         # Bazel version
├── BUILD.bazel           # Root build file
├── apps/
│   └── web/
│       └── BUILD.bazel
├── libs/
│   └── utils/
│       └── BUILD.bazel
└── tools/
    └── bazel/
        └── rules/

2. Key Concepts

Templates

Template 1: WORKSPACE Configuration

# WORKSPACE.bazel
workspace(name = "myproject")

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

# Rules for JavaScript/TypeScript
http_archive(
    name = "aspect_rules_js",
    sha256 = "...",
    strip_prefix = "rules_js-1.34.0",
    url = "https://github.com/aspect-build/rules_js/releases/download/v1.34.0/rules_js-v1.34.0.tar.gz",
)

load("@aspect_rules_js//js:repositories.bzl", "rules_js_dependencies")
rules_js_dependencies()

load("@rules_nodejs//nodejs:repositories.bzl", "nodejs_register_toolchains")
nodejs_register_toolchains(
    name = "nodejs",
    node_version = "20.9.0",
)

load("@aspect_rules_js//npm:repositories.bzl", "npm_translate_lock")
npm_translate_lock(
    name = "npm",
    pnpm_lock = "//:pnpm-lock.yaml",
    verify_node_modules_ignored = "//:.bazelignore",
)

load("@npm//:repositories.bzl", "npm_repositories")
npm_repositories()

# Rules for Python
http_archive(
    name = "rules_python",
    sha256 = "...",
    strip_prefix = "rules_python-0.27.0",
    url = "https://github.com/bazelbuild/rules_python/releases/download/0.27.0/rules_python-0.27.0.tar.gz",
)

load("@rules_python//python:repositories.bzl", "py_repositories")
py_repositories()

Template 2: .bazelrc Configuration

# .bazelrc

# Build settings
build --enable_platform_specific_config
build --incompatible_enable_cc_toolchain_resolution
build --experimental_strict_conflict_checks

# Performance
build --jobs=auto
build --local_cpu_resources=HOST_CPUS*.75
build --local_ram_resources=HOST_RAM*.75

# Caching
build --disk_cache=~/.cache/bazel-disk
build --repository_cache=~/.cache/bazel-repo

# Remote caching (optional)
build:remote-cache --remote_cache=grpcs://cache.example.com
build:remote-cache --remote_upload_local_results=true
build:remote-cache --remote_timeout=3600

# Remote execution (optional)
build:remote-exec --remote_executor=grpcs://remote.example.com
build:remote-exec --remote_instance_name=projects/myproject/instances/default
build:remote-exec --jobs=500

# Platform configurations
build:linux --platforms=//platforms:linux_x86_64
build:macos --platforms=//platforms:macos_arm64

# CI configuration
build:ci --config=remote-cache
build:ci --build_metadata=ROLE=CI
build:ci --bes_results_url=https://results.example.com/invocation/
build:ci --bes_backend=grpcs://bes.example.com

# Test settings
test --test_output=errors
test --test_summary=detailed

# Coverage
coverage --combined_report=lcov
coverage --instrumentation_filter="//..."

# Convenience aliases
build:opt --compilation_mode=opt
build:dbg --compilation_mode=dbg

# Import user settings
try-import %workspace%/user.bazelrc

Template 3: TypeScript Library BUILD

# libs/utils/BUILD.bazel
load("@aspect_rules_ts//ts:defs.bzl", "ts_project")
load("@aspect_rules_js//js:defs.bzl", "js_library")
load("@npm//:defs.bzl", "npm_link_all_packages")

npm_link_all_packages(name = "node_modules")

ts_project(
    name = "utils_ts",
    srcs = glob(["src/**/*.ts"]),
    declaration = True,
    source_map = True,
    tsconfig = "//:tsconfig.json",
    deps = [
        ":node_modules/@types/node",
    ],
)

js_library(
    name = "utils",
    srcs = [":utils_ts"],
    visibility = ["//visibility:public"],
)

# Tests
load("@aspect_rules_jest//jest:defs.bzl", "jest_test")

jest_test(
    name = "utils_test",
    config = "//:jest.config.js",
    data = [
        ":utils",
        "//:node_modules/jest",
    ],
    node_modules = "//:node_modules",
)

Template 4: Python Library BUILD

# libs/ml/BUILD.bazel
load("@rules_python//python:defs.bzl", "py_library", "py_test", "py_binary")
load("@pip//:requirements.bzl", "requirement")

py_library(
    name = "ml",
    srcs = glob(["src/**/*.py"]),
    deps = [
        requirement("numpy"),
        requirement("pandas"),
        requirement("scikit-learn"),
        "//libs/utils:utils_py",
    ],
    visibility = ["//visibility:public"],
)

py_test(
    name = "ml_test",
    srcs = glob(["tests/**/*.py"]),
    deps = [
        ":ml",
        requirement("pytest"),
    ],
    size = "medium",
    timeout = "moderate",
)

py_binary(
    name = "train",
    srcs = ["train.py"],
    deps = [":ml"],
    data = ["//data:training_data"],
)

Template 5: Custom Rule for Docker

# tools/bazel/rules/docker.bzl
def _docker_image_impl(ctx):
    dockerfile = ctx.file.dockerfile
    base_image = ctx.attr.base_image
    layers = ctx.files.layers

    # Build the image
    output = ctx.actions.declare_file(ctx.attr.name + ".tar")

    args = ctx.actions.args()
    args.add("--dockerfile", dockerfile)
    args.add("--output", output)
    args.add("--base", base_image)
    args.add_all("--layer", layers)

    ctx.actions.run(
        inputs = [dockerfile] + layers,
        outputs = [output],
        executable = ctx.executable._builder,
        arguments = [args],
        mnemonic = "DockerBuild",
        progress_message = "Building Docker image %s" % ctx.label,
    )

    return [DefaultInfo(files = depset([output]))]

docker_image = rule(
    implementation = _docker_image_impl,
    attrs = {
        "dockerfile": attr.label(
            allow_single_file = [".dockerfile", "Dockerfile"],
            mandatory = True,
        ),
        "base_image": attr.string(mandatory = True),
        "layers": attr.label_list(allow_files = True),
        "_builder": attr.label(
            default = "//tools/docker:builder",
            executable = True,
            cfg = "exec",
        ),
    },
)

Template 6: Query and Dependency Analysis

# 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)"

# Find all targets in a package
bazel query "//libs/..."

# Find changed targets since commit
bazel query "rdeps(//..., set($(git diff --name-only HEAD~1 | sed 's/.*/"&"/' | tr '\n' ' ')))"

# Generate dependency graph
bazel query "deps(//apps/web:web)" --output=graph | dot -Tpng > deps.png

# Find all test targets
bazel query "kind('.*_test', //...)"

# Find targets with specific tag
bazel query "attr(tags, 'integration', //...)"

# Compute build graph size
bazel query "deps(//...)" --output=package | wc -l

Template 7: Remote Execution Setup

# platforms/BUILD.bazel
platform(
    name = "linux_x86_64",
    constraint_values = [
        "@platforms//os:linux",
        "@platforms//cpu:x86_64",
    ],
    exec_properties = {
        "container-image": "docker://gcr.io/myproject/bazel-worker:latest",
        "OSFamily": "Linux",
    },
)

platform(
    name = "remote_linux",
    parents = [":linux_x86_64"],
    exec_properties = {
        "Pool": "default",
        "dockerNetwork": "standard",
    },
)

# toolchains/BUILD.bazel
toolchain(
    name = "cc_toolchain_linux",
    exec_compatible_with = [
        "@platforms//os:linux",
        "@platforms//cpu:x86_64",
    ],
    target_compatible_with = [
        "@platforms//os:linux",
        "@platforms//cpu:x86_64",
    ],
    toolchain = "@remotejdk11_linux//:jdk",
    toolchain_type = "@bazel_tools//tools/jdk:runtime_toolchain_type",
)

Performance Optimization

# Profile build
bazel build //... --profile=profile.json
bazel analyze-profile profile.json

# Identify slow actions
bazel build //... --execution_log_json_file=exec_log.json

# Memory profiling
bazel build //... --memory_profile=memory.json

# Skip analysis cache
bazel build //... --notrack_incremental_state

Best Practices

Do's

• Use fine-grained targets - Better caching
• Pin dependencies - Reproducible builds
• Enable remote caching - Share build artifacts
• Use visibility wisely - Enforce architecture
• Write BUILD files per directory - Standard convention

Don'ts

• Don't use glob for deps - Explicit is better
• Don't commit bazel- dirs* - Add to .gitignore
• Don't skip WORKSPACE setup - Foundation of build
• Don't ignore build warnings - Technical debt

Resources

• Bazel Documentation
• Bazel Remote Execution
• rules_js

AGI Framework Integration

Adapted for @techwavedev/agi-agent-kit Original source: antigravity-awesome-skills

Memory-First Protocol

Retrieve prior error resolutions and debugging strategies. The hybrid search excels here — BM25 finds exact error codes/stack traces while vectors find semantically similar past issues.

# Check for prior debugging/diagnostics context before starting
python3 execution/memory_manager.py auto --query "error patterns and debugging solutions for Bazel Build Optimization"

Storing Results

After completing work, store debugging/diagnostics decisions for future sessions:

python3 execution/memory_manager.py store \
  --content "Root cause: memory leak from unclosed DB connections in pool — fixed with context manager" \
  --type error --project <project> \
  --tags bazel-build-optimization debugging

Multi-Agent Collaboration

Store error resolutions so any agent encountering the same issue retrieves the fix instantly instead of re-debugging.

python3 execution/cross_agent_context.py store \
  --agent "<your-agent>" \
  --action "Debugged and resolved critical issue — root cause documented for future reference" \
  --project <project>

Self-Annealing Loop

When this skill resolves an error, store the fix in memory AND update the relevant directive. The system gets stronger with each resolved issue.

BM25 Exact Match

Error codes, stack traces, and log messages are best found via BM25 keyword search. The hybrid system automatically uses exact matching for these patterns.

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