linkerd-patterns – Security skill for AI agents

Linkerd Patterns

Production patterns for Linkerd service mesh - the lightweight, security-first service mesh for Kubernetes.

Do not use this skill when

• The task is unrelated to linkerd patterns
• 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.

Use this skill when

• Setting up a lightweight service mesh
• Implementing automatic mTLS
• Configuring traffic splits for canary deployments
• Setting up service profiles for per-route metrics
• Implementing retries and timeouts
• Multi-cluster service mesh

Core Concepts

1. Linkerd Architecture

┌─────────────────────────────────────────────┐
│                Control Plane                 │
│  ┌─────────┐ ┌──────────┐ ┌──────────────┐ │
│  │ destination │ │ identity │ │ proxy-inject │ │
│  └─────────┘ └──────────┘ └──────────────┘ │
└─────────────────────────────────────────────┘
                      │
┌─────────────────────────────────────────────┐
│                 Data Plane                   │
│  ┌─────┐    ┌─────┐    ┌─────┐             │
│  │proxy│────│proxy│────│proxy│             │
│  └─────┘    └─────┘    └─────┘             │
│     │           │           │               │
│  ┌──┴──┐    ┌──┴──┐    ┌──┴──┐            │
│  │ app │    │ app │    │ app │            │
│  └─────┘    └─────┘    └─────┘            │
└─────────────────────────────────────────────┘

2. Key Resources

| Resource | Purpose |

|----------|---------|

| ServiceProfile | Per-route metrics, retries, timeouts |

| TrafficSplit | Canary deployments, A/B testing |

| Server | Define server-side policies |

| ServerAuthorization | Access control policies |

Version and deployment boundaries

Examples mix version-specific APIs and partial manifests. Check the installed Linkerd/Kubernetes CRDs and supported Gateway API/SMI versions before rendering or applying; the Deployment fragment omits required selectors/containers. mTLS protects eligible meshed traffic, not all traffic automatically; verify injection, identities and explicit authorization. The broad unauthenticated CIDR example requires an intentional approved exception. Pin/review installer and image versions, preview rendered changes against the exact context/namespace, and preserve rollout/rollback access. Tap/log output may disclose sensitive traffic.

Templates

Template 1: Mesh Installation

# Install CLI
brew install linkerd

# Alternative: download the official installer, inspect it, then execute it
tmpdir="$(mktemp -d)"
trap 'rm -rf "$tmpdir"' EXIT
curl --proto '=https' --tlsv1.2 -sSfL https://run.linkerd.io/install -o "$tmpdir/linkerd-install.sh"
cat "$tmpdir/linkerd-install.sh"  # review the full installer before executing
sh "$tmpdir/linkerd-install.sh"

# Validate cluster
linkerd check --pre

# Install CRDs
linkerd install --crds | kubectl apply -f -

# Install control plane
linkerd install | kubectl apply -f -

# Verify installation
linkerd check

# Install viz extension (optional)
linkerd viz install | kubectl apply -f -

Template 2: Inject Namespace

# Automatic injection for namespace
apiVersion: v1
kind: Namespace
metadata:
  name: my-app
  annotations:
    linkerd.io/inject: enabled
---
# Or inject specific deployment
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
  annotations:
    linkerd.io/inject: enabled
spec:
  template:
    metadata:
      annotations:
        linkerd.io/inject: enabled

Template 3: Service Profile with Retries

apiVersion: linkerd.io/v1alpha2
kind: ServiceProfile
metadata:
  name: my-service.my-namespace.svc.cluster.local
  namespace: my-namespace
spec:
  routes:
    - name: GET /api/users
      condition:
        method: GET
        pathRegex: /api/users
      responseClasses:
        - condition:
            status:
              min: 500
              max: 599
          isFailure: true
      isRetryable: true
    - name: POST /api/users
      condition:
        method: POST
        pathRegex: /api/users
      # POST not retryable by default
      isRetryable: false
    - name: GET /api/users/{id}
      condition:
        method: GET
        pathRegex: /api/users/[^/]+
      timeout: 5s
      isRetryable: true
  retryBudget:
    retryRatio: 0.2
    minRetriesPerSecond: 10
    ttl: 10s

Template 4: Traffic Split (Canary)

apiVersion: split.smi-spec.io/v1alpha1
kind: TrafficSplit
metadata:
  name: my-service-canary
  namespace: my-namespace
spec:
  service: my-service
  backends:
    - service: my-service-stable
      weight: 900m  # 90%
    - service: my-service-canary
      weight: 100m  # 10%

Template 5: Server Authorization Policy

# Define the server
apiVersion: policy.linkerd.io/v1beta1
kind: Server
metadata:
  name: my-service-http
  namespace: my-namespace
spec:
  podSelector:
    matchLabels:
      app: my-service
  port: http
  proxyProtocol: HTTP/1
---
# Allow traffic from specific clients
apiVersion: policy.linkerd.io/v1beta1
kind: ServerAuthorization
metadata:
  name: allow-frontend
  namespace: my-namespace
spec:
  server:
    name: my-service-http
  client:
    meshTLS:
      serviceAccounts:
        - name: frontend
          namespace: my-namespace
---
# Allow unauthenticated traffic (e.g., from ingress)
apiVersion: policy.linkerd.io/v1beta1
kind: ServerAuthorization
metadata:
  name: allow-ingress
  namespace: my-namespace
spec:
  server:
    name: my-service-http
  client:
    unauthenticated: true
    networks:
      - cidr: 10.0.0.0/8

Template 6: HTTPRoute for Advanced Routing

apiVersion: policy.linkerd.io/v1beta2
kind: HTTPRoute
metadata:
  name: my-route
  namespace: my-namespace
spec:
  parentRefs:
    - name: my-service
      kind: Service
      group: ""
      port: 8080
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /api/v2
          headers:
            - name: x-api-version
              value: v2
      backendRefs:
        - name: my-service-v2
          port: 8080
    - matches:
        - path:
            type: PathPrefix
            value: /api
      backendRefs:
        - name: my-service-v1
          port: 8080

Template 7: Multi-cluster Setup

# On each cluster, install with cluster credentials
linkerd multicluster install | kubectl apply -f -

# Link clusters
linkerd multicluster link --cluster-name west \
  --api-server-address https://west.example.com:6443 \
  | kubectl apply -f -

# Export a service to other clusters
kubectl label svc/my-service mirror.linkerd.io/exported=true

# Verify cross-cluster connectivity
linkerd multicluster check
linkerd multicluster gateways

Monitoring Commands

# Live traffic view
linkerd viz top deploy/my-app

# Per-route metrics
linkerd viz routes deploy/my-app

# Check proxy status
linkerd viz stat deploy -n my-namespace

# View service dependencies
linkerd viz edges deploy -n my-namespace

# Dashboard
linkerd viz dashboard

Debugging

# Check injection status
linkerd check --proxy -n my-namespace

# View proxy logs
kubectl logs deploy/my-app -c linkerd-proxy

# Debug identity/TLS
linkerd identity -n my-namespace

# Tap traffic (live)
linkerd viz tap deploy/my-app --to deploy/my-backend

Best Practices

Do's

• Enable mTLS everywhere - It's automatic with Linkerd
• Use ServiceProfiles - Get per-route metrics and retries
• Set retry budgets - Prevent retry storms
• Monitor golden metrics - Success rate, latency, throughput

Don'ts

• Don't skip check - Always run linkerd check after changes
• Don't over-configure - Linkerd defaults are sensible
• Don't ignore ServiceProfiles - They unlock advanced features
• Don't forget timeouts - Set appropriate values per route

Resources

• [Linkerd Documentation](https://linkerd.io/2.14/overview/)
• [Service Profiles](https://linkerd.io/2.14/features/service-profiles/)
• [Authorization Policy](https://linkerd.io/2.14/features/server-policy/)

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.