How Flagger Works? - Istio Integration¶

In this document, we will explore how Flagger integrates with Istio to enable progressive delivery.

Core Concepts¶

Flagger is a progressive delivery tool that automates the release process for applications running on Kubernetes. It works by monitoring application metrics and gradually shifting traffic to new versions based on predefined rules and analysis.

It supports multiple routing providers, all with different levels of integration and features. Some of the supported routing providers include:

Istio
Linkerd
App Mesh
NGINX
Skipper
Contour
Gloo Edge
Traefik
Kuma
Gateway API
Apache APISIX
Knative

In this document, we will focus on how Flagger works with Istio since it supports a wide range of deployment strategies and advanced traffic management features. See Deployment Strategies for more details.

Deployment Strategies¶

Flagger supports various deployment strategies, including:

Canary Release: Gradually shifts traffic from the stable version to the new version in incremental steps based on predefined rules and metric analysis
A/B Testing: Routes traffic to different versions based on HTTP headers or cookies to compare performance and user behavior
Blue/Green: Switches traffic instantly from the old version (blue) to the new version (green) after validation
Blue/Green Mirroring: Mirrors production traffic to the new version for testing without affecting user requests, then switches when ready
Canary Release with Session Affinity: Gradually shifts traffic to the new version while maintaining user sessions on the same version using cookie-based routing

See Deployment Strategies for more details.

Metrics Analysis¶

During the deployment process, Flagger can continuously monitor the metrics we care about, such as error rate percentage, availability, or average response time. Common metric sources include Prometheus, CloudWatch, Datadog, New Relic, and others. See Metrics Analysis for more details.

Alerting¶

Flagger supports sending alerts to various channels, including Slack, Microsoft Teams, Rocket.Chat, and Discord.

At the global level, Slack and Microsoft Teams can be configured.

At the per Canary level, Slack, Microsoft Teams, Rocket.Chat and Discord can be configured. The canary analysis can be extended with a list of alerts that reference an AlertProvider.

See Alerting for more details.

CRDs¶

Canary: The Canary custom resource defines the deployment strategy, analysis metrics, and traffic routing rules for a specific application.
MetricTemplate: This resource allows users to define custom metrics for analysis during the deployment process.
AlertProvider: This resource configures alerting channels for deployment notifications.

Istio Integration¶

Flagger uses Istio's traffic management capabilities to perform canary deployments, A/B testing, traffic mirroring, and blue/green deployments. It leverages Istio's VirtualServices and DestinationRules to control the flow of traffic between different versions of an application.