Linkerd Patterns

# Linkerd Patterns

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

## When to Use This Skill

- 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                 │
│  ┌─────────┐ ┌──────────┐ ┌──────────────┐ │
│  │ destiny │ │ 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              |

## Templates

### Template 1: Mesh Installation

```bash
# Install CLI
curl --proto '=https' --tlsv1.2 -sSfL https://run.linkerd.io/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

```yaml
# 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

```yaml
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)

```yaml
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

```yaml
# D