cloud-platform-skills / skills

---
description: "Progressive delivery: Argo Rollouts and Flagger canaries with automated Prometheus analysis, blue-green cutover, Istio traffic shifting, and automatic rollback. Use when releasing to a small percentage of traffic first while watching error rate and latency, when a bad deploy must roll back automatically without a human, or when choosing between canary, blue-green and rolling deployment."
globs:
alwaysApply: false
---

# Progressive Delivery & Zero-Downtime Deployment Strategies

## When to Use This Skill

**Triggers — load this skill when:**

- A release must ship gradually with automated metric-based abort
- Blue-green vs canary vs rolling must be chosen for a specific workload
- A rollout needs rollback automation or traffic-shifting configuration

**Route elsewhere when:**

- Mesh-level routing and mTLS policy -> `api-gateway-service-mesh`
- Continuous delivery plumbing that triggers the rollout -> `gitops-multi-cluster-argo-flux`
- Analysis metric definition -> `sli-slo-error-budget-design`

## 1. Automated Canary with Argo Rollouts & Prometheus Analysis

```yaml
apiVersion: argoproj.io/v1alpha1
kind: Rollout
metadata:
  name: order-service
  namespace: production
spec:
  replicas: 10
  strategy:
    canary:
      analysis:
        templates:
          - templateName: success-rate-metric
        args:
          - name: service-name
            value: order-service
      steps:
        - setWeight: 5
        - pause: { duration: 5m }
        - setWeight: 20
        - pause: { duration: 10m }
        - setWeight: 50
        - pause: { duration: 10m }
```

### Automated Metric Analysis Template (`AnalysisTemplate`)

```yaml
apiVersion: argoproj.io/v1alpha1
kind: AnalysisTemplate
metadata:
  name: success-rate-metric
  namespace: production
spec:
  metrics:
    - name: http-success-rate
      interval: 1m
      successCondition: result[0] >= 0.999
      failureLimit: 2
      provider:
        prometheus:
          address: http://prometheus-k8s.monitoring:9090
          query: |
            sum(rate(http_requests_total{service="order-service",status!~"5.*"}[2m]))
            /
            sum(rate(http_requests_total{service="order-service"}[2m]))
```

---

## 2. Strategy Selection Guide

- **Blue/Green**: Best for workloads that cannot tolerate version coexistence or require instant atomic rollbacks.
- **Canary with Step Analysis**: Ideal for customer-facing high-throughput microservices where real-user metrics validate regression risk.
- **Shadow/Dark Traffic**: Forward duplicate production read traffic to candidate versions to test performance under true load without user impact.

---

## 3. Flagger with Istio Traffic Shifting

Argo Rollouts owns the workload; Flagger drives the mesh and works well when Istio already
carries the traffic policy:

```yaml
apiVersion: flagger.app/v1beta1
kind: Canary
metadata: { name: checkout, namespace: prod }
spec:
  provider: istio
  targetRef: { apiVersion: apps/v1, kind: Deployment, name: checkout }
  service:
    port: 8080
    gateways: [istio-system/public-gateway]
    hosts: [checkout.example.com]
    retries: { attempts: 3, perTryTimeout: 2s }
  analysis:
    interval: 1m
    threshold: 5              # failed checks before rollback
    maxWeight: 50
    stepWeight: 5             # 5% -> 10% -> ... automatic weighted shift
    metrics:
      - name: request-success-rate
        thresholdRange: { min: 99 }
        interval: 1m
      - name: request-duration
        thresholdRange: { max: 500 }
        interval: 1m
    webhooks:
      - name: load-test
        url: http://flagger-loadtester.prod/
        metadata: { cmd: "hey -z 1m -q 10 -c 2 http://checkout-canary:8080/" }
```

Flagger generates and owns the Istio `VirtualService`; do not hand-edit it or the next
reconciliation reverts the change. Under the hood both approaches do the same thing — shift a
weight, evaluate metrics over a window, promote or roll back — so choose by which control plane
already owns routing, not by feature lists.

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