Add Copilot instructions for fluent-operator

Author: marcofranssen

.github/copilot-instructions.md

@@ -0,0 +1,105 @@
+# Copilot Instructions for fluent-operator
+
+## Project Summary
+
+Fluent Operator is a Kubernetes operator (written in Go) that manages Fluent Bit and Fluentd deployments via Custom Resource Definitions (CRDs). It is built with **kubebuilder v3** and **controller-runtime**. The Go module path is `github.com/fluent/fluent-operator/v3`.
+
+- **Language**: Go (version specified in `go.mod`, currently 1.26.2)
+- **Framework**: kubebuilder / controller-runtime
+- **License**: Apache 2.0
+- **Default branch**: `master`
+
+## Build, Test, and Lint Commands
+
+Always run `go mod download` before building or testing.
+
+| Task | Command | Notes |
+|---|---|---|
+| **Download deps** | `go mod download` | Run first |
+| **Generate deepcopy** | `make generate` | Regenerates `zz_generated.deepcopy.go` files |
+| **Generate CRDs & manifests** | `make manifests` | Requires `kubectl` on PATH for kustomize steps |
+| **Build binaries** | `make build` | Runs generate + fmt + vet, outputs to `bin/` |
+| **Build only (no codegen)** | `make binary` | Builds `bin/fb-manager`, `bin/fb-watcher`, `bin/fd-watcher` |
+| **Run unit tests** | `make test` | Runs manifests + generate + fmt + vet + envtest setup, then `go test` with race detector. Excludes `/e2e` tests. |
+| **Run linter** | `make lint` | Uses golangci-lint v2 with config in `.golangci.yml` |
+| **Lint fix** | `make lint-fix` | Auto-fixes lint issues |
+| **Update API docs** | `make docs-update` | Runs `go run ./cmd/doc-gen/main.go` |
+| **Verify CRDs match** | `make verify` | Runs `hack/verify-crds.sh` and `hack/verify-codegen.sh` |
+| **Format** | `go fmt ./...` | |
+| **Vet** | `go vet ./...` | |
+
+### Important: After changing any API type in `apis/`
+
+Always run in this order:
+1. `make generate` — regenerates DeepCopy methods
+2. `make manifests` — regenerates CRD YAML files in `config/crd/bases/`, `charts/fluent-operator/crds/`, `charts/fluent-operator-crds/templates/`, and `manifests/setup/`
+3. `make docs-update` — regenerates API documentation
+
+CI will fail if generated files are out of date (`git diff --exit-code` is checked).
+
+### Tool versions (auto-installed to `./bin/`)
+
+- controller-gen: v0.18.0
+- kustomize: v5.6.0
+- golangci-lint: v2.6.2
+- ginkgo: v2.27.2
+- kind: v0.30.0
+
+## Repository Layout
+
+```
+apis/                        # CRD type definitions (the most commonly edited area)
+  fluentbit/v1alpha2/        # Fluent Bit CRDs — types, plugins, webhook
+    plugins/                 # Plugin type definitions (input, filter, output, parser)
+  fluentd/v1alpha1/          # Fluentd CRDs — types, plugins
+    plugins/                 # Fluentd plugin types (input, filter, output)
+  generated/                 # Generated client code
+cmd/
+  fluent-manager/            # Main operator binary entrypoint (main.go)
+  fluent-watcher/fluentbit/  # Fluent Bit watcher binary + Dockerfile
+  fluent-watcher/fluentd/    # Fluentd watcher binary + Dockerfile
+  doc-gen/                   # API doc generation tool
+controllers/                 # Reconciler implementations
+  fluentbit_controller.go
+  fluentbitconfig_controller.go
+  fluentd_controller.go
+  fluentdconfig_controller.go
+  collector_controller.go
+pkg/
+  operator/                  # Kubernetes resource builders for DaemonSet/StatefulSet
+  fluentd/                   # Fluentd config rendering
+  utils/                     # Shared utilities
+config/                      # kubebuilder/kustomize config (RBAC, CRD bases, webhooks)
+charts/                      # Helm charts (fluent-operator, fluent-operator-crds)
+manifests/                   # YAML manifests for kubectl-based deployment
+hack/                        # Shell scripts for verification and CRD mutation
+tests/                       # E2E test scripts and specs
+```
+
+## CI Checks (run on every PR)
+
+1. **Lint** (`.github/workflows/lint.yml`): `golangci-lint run` — runs on all pushes/PRs.
+2. **Tests** (`.github/workflows/test.yml`): `go mod tidy && make test` — runs on all pushes/PRs.
+3. **Main CI** (`.github/workflows/main.yaml`): Triggered on changes to Go/API/controller files:
+   - `make generate manifests docs-update` then `git diff --exit-code` (generated code must be committed)
+   - `make shellcheck` (shell script linting via Docker)
+   - `make test`
+   - `make verify` (CRDs and codegen match)
+   - `make binary` (binary build)
+4. **Helm CI** (`.github/workflows/helm-ci.yaml`): Helm chart linting and testing.
+
+## Coding Conventions
+
+- All API types use kubebuilder markers (`+kubebuilder:...`) for validation, defaulting, and CRD generation.
+- New Go files must include the Apache 2.0 license header (see `hack/boilerplate.go.txt`).
+- Commits require DCO sign-off (`Signed-off-by` line).
+- Linter config is in `.golangci.yml` — enabled linters include: errcheck, govet, staticcheck, revive, misspell, unused, ginkgolinter, and others.
+- Tests use Ginkgo/Gomega and envtest for controller tests.
+
+## Tips
+
+- Trust these instructions first. Only search the repo if information here is incomplete or incorrect.
+- The `make test` target handles envtest binary setup automatically.
+- When adding a new Fluent Bit or Fluentd plugin, add the type in `apis/fluentbit/v1alpha2/plugins/` or `apis/fluentd/v1alpha1/plugins/`, then wire it into the relevant config type and run all three generation steps.
+- The `manifests/setup/setup.yaml` file is auto-generated — never edit it directly.
+- CRD files in `config/crd/bases/` and `charts/` are auto-generated — never edit them directly.