Ark Controller Development

Ark Controller Development

Guidance for developing the Ark Kubernetes operator in ark/.

When to use this skill

• Modifying Go type definitions (api/v1alpha1/*_types.go)
• Fixing CRD/Helm chart sync errors
• Adding new CRD fields or resources

CRD Generation Flow

api/v1alpha1/*_types.go     # Go types with markers
        ↓
    make manifests          # Generates CRDs and syncs to Helm chart
        ↓
config/crd/bases/*.yaml     # Source CRDs (auto-generated)
dist/chart/templates/crd/   # Helm chart CRDs (auto-synced)

make manifests automatically syncs source CRDs to the Helm chart while preserving templated headers.

Fixing "CRDs out of sync" Errors

When make build fails with CRD validation errors:

cd ark
make manifests
make build

Key Directories

Common Tasks

After Modifying Types or Comments

Go type comments become CRD field descriptions:

cd ark
make manifests
make build

After Any Go Code Change

make lint-fix    # Format and auto-fix what the linter can fix
make lint        # Fail fast on issues CI will reject — MANDATORY
make build       # Build and validate
make test        # Run unit + envtest suites

Before Opening a PR

Run the chainsaw e2e suite against a live cluster — unit + envtest don't exercise the full apply → reconcile → status loop. Prefer the deterministic mock-llm suite; only run the LLM-backed tests when the change specifically touches that path (saves cost + avoids flakes from real LLM providers).

# Deterministic suite (default)
(cd tests && chainsaw test --selector '!llm')

# LLM suite — only when your change needs it
(cd tests && chainsaw test --selector 'llm')

See the chainsaw skill for patterns and antipatterns (e.g. prefer chainsaw assert over shell grep; prefer wait over polling).

make lint runs the same golangci-lint rules CI enforces. Running it locally before pushing is non-negotiable — red PR checks cost more than the minute the lint takes.

Leverage Existing Code — Don't Reinvent

Before writing a parser, struct, helper, retry loop, URL builder, or any utility, check whether it already exists in:

1. Go standard library.
2. Direct or transitive dependencies in go.mod (controller-runtime, apimachinery, the SDK for whatever spec you're implementing, golang.org/x/...).

Hand-rolled code drifts, duplicates tests, and becomes maintenance burden. A short adapter delegating to a library is almost always better than a reimplementation.

Heuristic: if the thing you're writing mirrors an existing spec, file format, header syntax, or common infra pattern, someone has already written it. Search first: go doc <import-path>, ls $(go env GOMODCACHE)/<dep>.

Re-export library types via alias (type X = lib.X) rather than defining a parallel struct with the same fields.

Worked example

Started this project by hand-rolling a WWW-Authenticate parser, RFC 9728 struct, RFC 8414 struct, and HTTP fetchers — ~150 LOC. The go-sdk already shipped them in oauthex:

// Bad — 40-line parser, partial struct, duplicated HTTP wrapper.
func parseHeader(h string) (string, bool) { /* ... */ }
type Metadata struct { /* partial mirror of RFC */ }
func fetch(ctx, url) (*Metadata, error) { /* 30 lines */ }

// Good — thin adapter, full spec support, ~10 LOC.
import "github.com/modelcontextprotocol/go-sdk/oauthex"
type Metadata = oauthex.ProtectedResourceMetadata
func Fetch(ctx context.Context, metaURL, resourceURL string, timeout time.Duration) (*Metadata, error) {
    return oauthex.GetProtectedResourceMetadata(ctx, metaURL, resourceURL, &http.Client{Timeout: timeout})
}

Same principle applies to retry/backoff (k8s.io/apimachinery/pkg/util/wait), JSON patch (strategicpatch), condition updates (meta.SetStatusCondition), HTTP clients, workqueues — whatever you're touching, check the existing deps first.

Avoid Magic Numbers — Reuse Configurable Values

Never inline numeric durations, retry counts, or buffer sizes. Priority:

1. User-configurable spec field — if the resource already has spec.timeout, spec.pollInterval, spec.retries, use it. One operator knob should govern all related code paths in the same reconcile.
2. Package-level const with a name explaining why that number.
3. Test-local const (e.g. const testTimeout = 5 * time.Second) — never inline literals in tests.

Worked example

// Bad — parallel constant invented out of thin air.
const discoveryTimeout = 10 * time.Second
client := &http.Client{Timeout: discoveryTimeout}

// Good — plumb the MCPServer's spec.timeout; single source of truth.
func Fetch(ctx, url string, timeout time.Duration) ...
timeout := parseTimeout(mcpServer.Spec.Timeout)

Testing — not optional

Every code change ships with tests. A PR touching ark/internal/ with no _test.go is incomplete. Applies to controller branches, webhooks, helpers — not just public APIs.

Required coverage for a controller branch:

• Happy path → expected status + conditions.
• Each failure mode → distinct stable condition reason (no string-matching).
• Idempotency → re-reconcile doesn't emit duplicate events or bump lastTransitionTime.
• Regression guard → pre-existing branches unaffected.

Completion Checklist

Before saying "done":

• make manifests clean (if types changed)
• make lint clean — same rules CI enforces
• make build green
• make test green — paste or reference output
• Chainsaw deterministic suite (chainsaw test --selector '!llm') green; LLM suite only if change requires it
• New _test.go exists for every new function / branch
• Helm chart CRDs regenerated and committed
• OpenAPI / Python SDK / TypeScript SDK regenerated if CRD changed
• Running pod re-verified — devspace syncs source, but only a container restart picks up new Go binaries; tail controller logs after any reconciliation-path change