# Flagger — Progressive Delivery Operator for Kubernetes

> Flagger is a FluxCD progressive delivery operator that automates canary, A/B, and blue/green rollouts on Kubernetes, using service-mesh traffic shifting and metric-based analysis to promote or abort releases.

## Install

Save as a script file and run:

# Flagger — Progressive Delivery Operator for Kubernetes

## Quick Use
```bash
# Install Flagger against a Linkerd mesh (works with Istio, App Mesh, NGINX, Contour, etc.)
helm repo add flagger https://flagger.app
helm upgrade -i flagger flagger/flagger 
  --namespace linkerd 
  --set meshProvider=linkerd 
  --set metricsServer=http://prometheus.linkerd-viz:9090

# Declare a canary for an existing Deployment
cat <<EOF | kubectl apply -f -
apiVersion: flagger.app/v1beta1
kind: Canary
metadata: { name: podinfo, namespace: prod }
spec:
  targetRef: { apiVersion: apps/v1, kind: Deployment, name: podinfo }
  service:   { port: 9898 }
  analysis:
    interval: 30s
    threshold: 5
    maxWeight: 50
    stepWeight: 10
    metrics:
      - name: request-success-rate
        thresholdRange: { min: 99 }
EOF
```

## Introduction
Flagger turns Kubernetes Deployments into safe, automated rollouts. Instead of "kubectl set image and pray", Flagger creates a canary Deployment alongside the primary, shifts a small slice of traffic through the service mesh, queries Prometheus (or Datadog, New Relic, CloudWatch) on a schedule, and promotes only if success-rate and latency meet thresholds. Fail the analysis and it rolls back. It''s part of the FluxCD family and graduated through the CNCF Sandbox.

## What Flagger Does
- Runs canary analysis with configurable steps, intervals, and metric thresholds.
- Supports traffic shifting via Istio, Linkerd, App Mesh, Gloo, Contour, NGINX, Traefik, Kuma, and OSM.
- Queries Prometheus, Datadog, New Relic, Dynatrace, CloudWatch, or Graphite for promotion signals.
- Runs webhook-driven load generation, acceptance tests, and post-promotion hooks.
- Handles Deployment, DaemonSet, StatefulSet, and custom resources with `primaryScalerReplicas`.

## Architecture Overview
Flagger is a Kubernetes operator watching Canary custom resources. When spec.image changes on the referenced target, it copies the current primary into a canary Deployment and, depending on strategy, creates the mesh resources (VirtualServices, TrafficSplits, etc.) needed to split traffic between primary and canary. A reconcile loop steps the weight up on success, queries metric providers, and either promotes (copies canary spec into primary, scales canary to zero) or rolls back. Deployment strategies include canary, A/B, blue/green, and traffic mirroring.

## Self-Hosting & Configuration
- Install via the official Helm chart; one Flagger per mesh provider, not per namespace.
- Point `metricsServer` at your Prometheus or configure a Datadog / New Relic provider with secrets.
- Annotate target Deployments to opt into Flagger management; others are untouched.
- Use `webhooks` to call k6, Locust, or smoke tests before each weight step.
- Keep `alertmanager` wired in — Flagger sends slack/msteams/webhook alerts on canary events.

## Key Features
- Multi-mesh: one control plane that speaks to Istio, Linkerd, App Mesh, and more.
- Progressive traffic shifting or session-affinity A/B testing via HTTP headers/cookies.
- MetricTemplates as first-class CRDs for reusable PromQL/NRQL/Datadog queries.
- Prometheus Operator integration for shipping standard dashboards.
- GitOps-friendly — canaries are declarative YAML managed by Flux or Argo CD.

## Comparison with Similar Tools
- **Argo Rollouts** — Works without a service mesh (direct Deployment replicas and traffic providers); similar feature set.
- **Spinnaker + Kayenta** — Heavier multi-cloud CD; Flagger is lighter and Kubernetes-only.
- **Istio Gateway API manual rollouts** — DIY; Flagger automates traffic shifting + analysis.
- **Helm + feature flags** — App-level toggles; doesn''t provide traffic-shifting canaries.
- **Managed Delivery (Keel)** — Spinnaker-centric; Flagger fits GitOps stacks already using Flux or Argo.

## FAQ
**Q:** Do I need a service mesh?
A: Strongly recommended for canary weight shifting. For mesh-less, use Nginx or Contour providers.

**Q:** What if my metric provider has a blip?
A: Flagger tolerates up to `threshold` consecutive failures before rollback to avoid flapping.

**Q:** Can I do blue/green with manual gate?
A: Yes — use the `approve-gate` webhook to pause until an operator approves promotion.

**Q:** Does it work with Argo CD?
A: Yes — Flagger manages the canary, Argo CD manages the desired state. No direct conflict.

## Sources
- https://github.com/fluxcd/flagger
- https://docs.flagger.app/


---
Source: https://tokrepo.com/en/workflows/6ac8ac2c-3929-11f1-9bc6-00163e2b0d79
Author: Script Depot