Admission Control

Grafana LabsOfficialPublished by Grafana Labs

Skill
Tool integration
Cloud and DevOps
Apache-2.0
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From the author

Use when the user asks to "write a validator", "add validation", "implement admission control", "write a mutating webhook", "add a mutation handler", "validate incoming resources", "implement admission logic", "add admission webhooks", "write ingress validation", or asks how to validate or mutate resources before they are persisted in a grafana-app-sdk app. Provides guidance on implementing validation and mutation admission handlers for grafana-app-sdk apps.

— the description by Grafana Labs

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides guidance on implementing admission control handlers for grafana-app-sdk applications. It covers the two primary types of admission: validation, which accepts or rejects requests, and mutation, which modifies resources before they are persisted. The guide explains how to implement the Validator and Mutator interfaces, register these handlers within the application, and follow best practices for error reporting and cross-field validation.

What it does

Defines the Validator interface for accepting or rejecting resource requests.
Defines the Mutator interface for modifying resources before persistence.
Provides patterns for immutability checks and cross-field validation.
Explains how to register admission handlers in the app configuration.
Details the differences between standalone operator and in-process plugin deployment modes.
Offers conventions for creating clear, user-actionable error messages.

When to use it

When you need to enforce business logic constraints on incoming resource requests.
When you need to set default values or normalize fields before saving a resource.
When you need to ensure certain fields remain immutable after resource creation.
When you need to validate that a referenced resource exists before allowing an operation.
When implementing custom admission logic for a grafana-app-sdk application.

Advantages

Consistent admission logic regardless of deployment mode.
Clear separation between validation and mutation concerns.
Standardized patterns for common Kubernetes-style validation tasks.
Integration with the native grafana-app-sdk lifecycle.

Usage examples

“How do I implement a validator to ensure a field is required in my grafana-app-sdk app?”: The agent provides the Validator interface implementation, showing how to check the field in the Validate method and return an error if it is empty.
“How can I set a default value for a field during resource creation?”: The agent provides a Mutator example demonstrating how to check for the AdmissionActionCreate action and update the object fields before returning the response.
“Where do I register my admission handlers in the app code?”: The agent shows the New function in pkg/app/app.go, demonstrating how to add Validator and Mutator instances to the ManagedKinds configuration.

Install

Download the skill as a ZIP:
https://mp-staging.autogineer.com/agent-skills/grafana/admission-control/download

Unzip it into the cross-client skills folder of your project:

mkdir -p .agents/skills && unzip admission-control.zip -d .agents/skills

Documentation by Grafana Labs

Admission Control

Admission control intercepts resource create/update requests before they are persisted. In grafana-app-sdk there are two types:

Validation — accept or reject a request; cannot modify the resource
Mutation — modify the resource before it is persisted (e.g. set defaults, normalize fields)

The app business logic for admission is identical whether the app runs as a standalone operator or inside grafana/apps. The only difference is the runtime: standalone apps stand up their own webhook server; grafana/apps apps have admission auto-registered as a Kubernetes plugin.

Getting Stubs

For standalone apps, if pkg/app/app.go does not yet exist, a stub App can be generated with:

grafana-app-sdk project component add operator

This creates scaffolded simple.App which admission handlers can be added to for each kind in ManagedKinds.

Validator Interface

// Implement this interface for each kind you want to validate
type Validator interface {
    Validate(ctx context.Context, request *app.AdmissionRequest) error
}

Return nil to admit the request
Return an error to reject it (the error message is returned to the API caller)
app.AdmissionRequest provides access to the incoming object and operation type
You can use k8s.NewAdmissionError(err error, statusCode int, reason string) (from "github.com/grafana/grafana-app-sdk/k8s") to better control the returned error information

Validator Example

type MyKindValidator struct{}

func (v *MyKindValidator) Validate(ctx context.Context, req *app.AdmissionRequest) error {
    obj, ok := req.Object.(*v1.MyKind)
    if !ok {
        return fmt.Errorf("admission request object was of invalid type %T (expected *v1.MyKind)", req.Object)
    }

    // Validate spec fields
    if obj.Spec.Title == "" {
        return fmt.Errorf("spec.title is required")
    }

    if obj.Spec.Count < 0 {
        return fmt.Errorf("spec.count must be non-negative, got %d", obj.Spec.Count)
    }

    // Distinguish create vs update
    if req.Action == resource.AdmissionActionUpdate && req.OldObject != nil {
        old, ok := req.OldObject.(*v1.MyKind)
        if !ok {
            return fmt.Errorf("admission request old object was of invalid type %T (expected *v1.MyKind)", req.OldObject)
        }
        if old.Spec.Title != obj.Spec.Title {
            return fmt.Errorf("spec.title is immutable after creation")
        }
    }

    return nil
}

Mutating Admission (Mutator)

// Implement this interface to mutate resources before persistence
type Mutator interface {
    Mutate(ctx context.Context, request *app.AdmissionRequest) (*app.MutatingResponse, error)
}

Return a MutatingResponse containing the (optionally modified) object
Return an error to reject the request entirely
Best practice is to reject requests from validators, not mutators

Mutating Handler Example

type MyKindMutator struct{}

func (m *MyKindMutator) Mutate(
    ctx context.Context,
    req *app.AdmissionRequest,
) (*app.MutatingResponse, error) {
    obj, ok := req.Object.(*v1.MyKind)
    if !ok {
        return nil, fmt.Errorf("admission request object was of invalid type %T (expected *v1.MyKind)", req.Object)
    }

    // Set defaults on create
    if req.Action == resource.AdmissionActionCreate {
        if obj.Spec.Description == "" {
            obj.Spec.Description = "No description provided"
        }
    }

    return &app.MutatingResponse{UpdatedObject: obj}, nil
}

Registering Admission Handlers

func New(cfg app.Config) (app.App, error) {
    cfg.KubeConfig.APIPath = "/apis"
    a, err := simple.NewApp(simple.AppConfig{
        ManagedKinds: []simple.AppManagedKind{
            {
                Kind:      v1.MyKindKind(),
                Validator: &MyKindValidator{},
                Mutator:   &MyKindMutator{},
            },
        },
    })
    if err != nil {
      return nil, fmt.Errorf("error creating app: %w", err)
    }
    if err = a.ValidateManifest(cfg.ManifestData); err != nil {
        return nil, fmt.Errorf("app manifest validation failed: %w", err)
    }
    return a, nil
}

Note that mutation and validation must also be enabled in the kind's CUE definition (mutation.operations and validation.operations fields) — see the cue-kind-definition skill for details.

Admission Request Fields

Key fields available on app.AdmissionRequest:

Field	Type	Description
`Object`	`resource.Object`	The incoming resource (after decoding)
`OldObject`	`resource.Object`	Previous state (only on UPDATE operations)
`Action`	`resource.AdmissionAction`	`AdmissionActionCreate`, `AdmissionActionUpdate`, `AdmissionActionDelete`, `AdmissionActionConnect`
`UserInfo`	`resource.AdmissionUserInfo`	The user making the request
`Kind`	`string`	The `Object` kind
`Group`	`string`	The `Object` API Group
`Version`	`string`	The `Object` API Version

Validation Patterns

Common patterns to implement:

// Immutability check
if req.Action == resource.AdmissionActionUpdate && old.Spec.ImmutableField != obj.Spec.ImmutableField {
    return fmt.Errorf("spec.immutableField cannot be changed after creation")
}

// Cross-field validation
if obj.Spec.StartTime.After(obj.Spec.EndTime) {
    return fmt.Errorf("spec.startTime must be before spec.endTime")
}

// Referential validation (e.g. check referenced resource exists)
if _, err := v.client.Get(ctx, resource.Identifier{Name: obj.Spec.RefName, Namespace: obj.Namespace}); err != nil {
    return fmt.Errorf("referenced resource %q not found", obj.Spec.RefName)
}

Deployment Difference

Mode	Admission runtime
Standalone operator	App starts a webhook server; Kubernetes routes admission requests to it
`grafana/apps`	Admission handlers are auto-registered as a Kubernetes in-process plugin — no separate server required

The handler code itself is identical in both cases.

Resources

Files

ATTRIBUTION.mdAdded by AutoGineer857 B
LICENSELicence file added by AutoGineer11.1 KiB
SKILL.md6.7 KiB
references/admission-patterns.md8.2 KiB

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Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

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Attribution and licence

Published by

Grafana Labs

Publisher

Grafana Labs (Official)

Source

grafana/skills · skills/grafana-app-sdk/admission-control · commit 8fb72a5

Licence

Apache License 2.0 (redistribution allowed)

LICENSE (added by AutoGineer from LICENSE)
ATTRIBUTION.md (written by AutoGineer)

Synced

2026-11-08

AutoGineer is not affiliated with or endorsed by Grafana Labs.

Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download admission-control.zip

From the author

AutoGineer summary

What it does

When to use it

Advantages

Usage examples

Install

Documentation by Grafana Labs

Admission Control

Getting Stubs

Validator Interface

Validator Example

Mutating Admission (Mutator)

Mutating Handler Example

Registering Admission Handlers

Admission Request Fields

Validation Patterns

Deployment Difference

Resources

Files

LICENSE

Requirements and compatibility

Security

Attribution and licence

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