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kgateway AI Agent Instructions

Project Overview

kgateway is a control plane implementing the Kubernetes Gateway API for Envoy. It's built on KRT (Kubernetes Declarative Controller Runtime from Istio) and uses a plugin-based architecture for extensibility.

Architecture (Read This First!)

Translation Pipeline (3 phases)

  1. Policy → IR: Plugins translate CRDs to PolicyIR (close to Envoy protos). Done once per policy CRD change.
  2. HTTPRoute/Gateway → IR with Policies Attached: Core kgateway aggregates routes/gateways and performs policy attachment via targetRefs.
  3. IR → xDS: Translates to Envoy config. Plugins provide NewGatewayTranslationPass functions called during route/listener translation.

See /devel/architecture/overview.md and the translation diagram at /devel/architecture/translation.svg.

Key Components

  • cmd/: 3 binaries: kgateway (controller), envoyinit (does some envoy bootstrap config manipulation), sds (secret server)
  • api/v1alpha1/kgateway/: kgateway CRD definitions. Use +kubebuilder markers for validation/generation
  • pkg/pluginsdk/: Plugin interfaces (Plugin, PolicyPlugin, BackendPlugin)
  • pkg/kgateway/extensions2/plugins/: Plugin implementations (trafficpolicy, httplistenerpolicy, etc.)
  • pkg/kgateway/krtcollections/: KRT collections for core resources
  • test/e2e/: End-to-end tests using custom framework (see test/e2e/README.md)

Plugin System

At the core kgateway translates kubernetes Gateway API resources to Envoy configuration. To add features like policies, or backends, we use a plugin system. Each plugin contributes to the translation, usually by adding a new type of CRD (most commonly a Policy CRD) that users can create to express their desired configuration.

Policy CRDs are attached to Gateway API resources via targetRefs or targetSelectors. kgateway manages the attachment of policies to the appropriate resources during translation.

The plugin is then called in the translation process to affect the dataplane configuration. To do this efficiently, the plugin should convert the CRD to an intermediate representation (IR) that is as close to Envoy protos as possible. This minimizes the amount of logic needed in the final translation, and allows for better status reflected back to the user if there are errors.

Plugins are stateless across translations but maintain state during a single gateway translation via ProxyTranslationPass. Each plugin:

  • Provides a KRT collection of ir.PolicyWrapper (contains PolicyIR + TargetRefs)
  • Implements NewGatewayTranslationPass(tctx ir.GwTranslationCtx, reporter reporter.Reporter) ir.ProxyTranslationPass
  • Can process backends via ProcessBackend, PerClientProcessBackend, or PerClientProcessEndpoints

Example: /pkg/kgateway/extensions2/plugins/trafficpolicy/traffic_policy_plugin.go

Development

Critical Developer Patterns

go build tag e2e

If you intend to include all source code, run 'go' commands that accept '-tags' with '-tags e2e'.

IR Equals() Methods (STRICTLY ENFORCED)

IRs output by KRT collections must implement Equals(other T) bool:

  • Compare ALL fields or mark with // +noKrtEquals (last line of comment)
  • Never use reflect.DeepEqual (flagged by custom analyzer in /hack/krtequals/)
  • Use proto equality helpers: proto.Equal(), not ==

Code Generation Workflow

Common targets:

  • make generate-code: Ignores stamp files, generates all (takes around 30 seconds)
  • make generate-all: Uses stamp files, only regenerates changed code (fast)
  • make verify: CI target - always regenerates everything, checks git diff
  • make go-generate-apis: Only API changes (~1m)
  • make fmt or make fmt-changed: Format code (always run before commit)

After API changes: Run make go-generate-apis then make fmt-changed. The Makefile uses dependency tracking in _output/stamps/. If not sure, just run make generate-all.

Testing Conventions

  • Unit tests: For new code, avoid Ginkgo. You may use Gomega matchers if appropriate.
  • E2E tests: Use framework in /test/e2e/ - DO NOT directly kubectl apply in tests
  • Custom matchers: /test/gomega/matchers/ (e.g., HaveHttpResponse)
  • Transforms: Compose matchers with WithTransform() (see /devel/testing/writing-tests.md)
  • Prefer explicit error checking: Expect(err).To(MatchError("msg")) over HaveOccurred()
  • Add descriptions: Expect(x).To(BeEmpty(), "list should be empty on init")

Run tests:

make test TEST_PKG=./path/to/package  # Unit tests
make e2e-test TEST_PKG=./test/e2e/tests/...  # E2E tests
make unit  # All unit tests (excludes e2e)

API/CRD Development

Adding New CRDs

  1. Create *_types.go in api/v1alpha1/ with +kubebuilder markers. You can use +kubebuilder:validation:AtLeastOneOf or +kubebuilder:validation:ExactlyOneOf for field groups.
  2. Required fields: Use +required, NO omitempty tag
  3. Optional fields: Use +optional, pointer types (except slices/maps), omitempty tag
  4. Durations: Use metav1.Duration with CEL validation
  5. Document defaults with +kubebuilder:default=...
  6. Run make go-generate-apis (generates CRDs, clients, RBAC in helm chart)
  7. Register CRD to the client in pkg/apiclient/types.go
  8. Add the CRD to the fake client's filterObjects in pkg/apiclient/fake/fake.go and AllCRDs in test/testutils/crd.go.

See /api/README.md for full guidelines.

Adding fields to Policy CRDs

  1. Add the field to the appropriate Spec struct in the CRD Go type in api/v1alpha1/.
  2. Add validation markers as needed (e.g., +kubebuilder:validation:MinLength=1, +optional, etc.)
  3. Run make go-generate-apis to regenerate code.
  4. Update the IR struct in the plugin package (pkg/kgateway/extensions2/plugins/<plugin_name>/) to include the new field.
  5. Add yaml tests cases in pkg/kgateway/translator/gateway/gateway_translator_test.go. The yaml inputs go in pkg/kgateway/translator/gateway/testutils/inputs/. DO NOT create the outputs by yourself. Instead, run your tests with environment variable REFRESH_GOLDEN=true. For example: REFRESH_GOLDEN=true go test -timeout 30s -run ^TestBasic$/^ListenerPolicy_with_proxy_protocol_on_HTTPS_listener$ github.com/kgateway-dev/kgateway/v2/pkg/kgateway/translator/gateway It will generate the outputs for you automatically in the pkg/kgateway/translator/gateway/testutils/outputs/ folder. Once the outputs are generated, inspect them to see they contain the changes you expect, and alert the user if that's not the case.
  6. For non-trivial changes, also add unit tests.
  7. Consider also adding E2E tests using the framework. You can look at test/e2e/features/cors/suite.go as an example for an E2E test. When writing an E2E test, prefer to use base.NewBaseTestingSuite as the base suite, as it provides many useful utilities. If you are adding a new test suite, remember to register it in test/e2e/tests/kgateway_tests.go. Additionally add it to one of the test kind clusters in .github/workflows/e2e.yaml.

Directory Conventions

  • Avoid "util" packages - use descriptive names
  • Lowercase filenames, underscores for Go files (my_file.go), dashes for docs (my-doc.md)
  • Package names: Avoid separators, use nested dirs for multi-word names
  • VSCode markers: Use // MARK: Section Name for long file navigation

Development Workflows

Local Development with Tilt

# Initial setup
ctlptl create cluster kind --name kind-kind --registry=ctlptl-registry

# Build images and load into kind
VERSION=v1.0.0-ci1 CLUSTER_NAME=kind make kind-build-and-load  # Builds all 3 images

# Deploy with Tilt (live reload enabled)
tilt up  # Configure via tilt-settings.yaml

# as long as tilt is running, it will auto-reload on code changes

See Tiltfile and tilt-settings.yaml for configuration.

Manual Development

# Set up complete development environment
make run  # kind + CRDs + MetalLB + images + charts

# Update after code change
make kind-reload-kgateway

Running Conformance Tests

make conformance  # Gateway API conformance
make all-conformance  # All suites

# Run specific test by ShortName
make conformance-HTTPRouteSimpleSameNamespace

Common Gotchas

  1. IR Equals() bugs: High-risk area. MUST compare all fields or mark +noKrtEquals.
  2. Proto comparison: Use proto.Equal(), not == or reflect.DeepEqual
  3. Codegen stamps: make clean-stamps if regeneration seems stuck
  4. E2E test resources: Never manually delete resources in specific order - let framework handle it
  5. PolicyIR translation: Translate as close to Envoy protos as possible in the Plugin IR, not in translation pass. The translation pass should be very light weight.
  6. KRT collections: Changes trigger minimal recomputation - dependencies tracked automatically
  7. Envoy image version: Defined in Makefile as ENVOY_IMAGE (update with care)

File Reference Quick Guide

  • Architecture: /devel/architecture/overview.md
  • Contributing: /devel/contributing/README.md
  • API conventions: /api/README.md
  • Testing guide: /devel/testing/writing-tests.md
  • Code generation: /devel/contributing/code-generation.md
  • E2E framework: /test/e2e/README.md
  • Plugin SDK: /pkg/pluginsdk/types.go
  • Example plugin: /pkg/kgateway/extensions2/plugins/trafficpolicy/

Build Details

  • Go version: Specified in go.mod
  • Base image: Alpine 3.17.6 (distroless for production)
  • Architectures: amd64, arm64 (controlled via GOARCH)
  • Image registry: ghcr.io/kgateway-dev (override via IMAGE_REGISTRY)
  • Rust components: envoyinit includes dynamic filters built from /internal/envoyinit/rustformations/

Key Make Targets

make help               # Self-documenting targets
make analyze            # Run golangci-lint (custom config)
make test               # Run unit tests
make e2e-test          # Run e2e tests
make generate-all       # Smart codegen (uses stamps)
make verify            # CI codegen check (always regenerates)
make fmt               # Format all code
make fmt-changed       # Format only changed files
make kind-create       # Create kind cluster
make setup             # Full local setup
make deploy-kgateway   # Deploy to cluster

Dependencies & Bumping

make bump-gtw DEP_REF=v1.3.0     # Bump Gateway API
make generate-licenses            # Update license attribution

Gateway API version is in go.mod and CRD install URL in Makefile (CONFORMANCE_VERSION).

Opening Pull Requests

  1. Ensure all linters pass: make analyze, make verify
  2. If you modified files in .github/: Run make lint-actions to lint GitHub Actions workflows
  3. Ensure tests pass in CI (unit + e2e + conformance)
  4. Use the PR template structure below

PR Body Structure

Every PR must include these sections:

  1. Description - Explain motivation, what changed, and link issues (Fixes #123)

  2. Change Type - Include one or more /kind commands in the PR body:

    • /kind feature, /kind fix, /kind cleanup, /kind documentation
    • /kind breaking_change, /kind deprecation, /kind design
    • /kind bump, /kind flake, /kind install

  3. Changelog - A fenced code block with release-note as the language identifier containing the release note text, or NONE if not user-facing

  4. Additional Notes (optional) - Extra context for reviewers

Style

All code and comments should use American English spelling (i.e. "color" not "colour", "honor" not "honour").

Markdown Output

When generating markdown documentation:

  • Use ordered heading levels (no skipping from # to ###)
  • Headings should not end in punctuation
  • Use consistent bullet types within a list (don't mix - and *)
  • No empty headings
  • Use -> instead of → for arrows (ASCII-compatible)
  • Prefer mermaid diagrams over ASCII art - use fenced mermaid code blocks for flowcharts, sequence diagrams, and architecture diagrams instead of box-drawing characters (┌ └ │ ├ ─ ► ▼ etc.)