ExternalDNS is a Kubernetes controller that synchronizes exposed Kubernetes Services and Ingresses with external DNS providers, enabling dynamic DNS record management through Kubernetes resources. Written in Go, it functions as a DNS controller that bridges Kubernetes clusters with public DNS servers, allowing cluster resources to be discoverable via external DNS infrastructure. Unlike Kubernetes' internal DNS server, ExternalDNS does not operate as a DNS server itself but instead configures external DNS providers such as AWS Route 53 and Google Cloud DNS based on Kubernetes resource definitions.
The core functionality of ExternalDNS involves retrieving a list of resources from the Kubernetes API, determining the desired DNS records, and then configuring external DNS providers accordingly. It operates in a DNS provider-agnostic manner, allowing users to control DNS records dynamically through Kubernetes resources. The controller can manage selected zones through domain filtering and synchronizes Ingresses, Services of type LoadBalancer, and nodes across multiple DNS providers. By default, ExternalDNS maintains awareness of the records it manages, enabling safe operation within non-empty hosted zones. Users can configure the controller with a unique txt-owner-id value to track ownership of DNS records throughout the cluster's lifetime, and a dry-run mode is available to preview changes before submission to DNS provider APIs.
The repository demonstrates significant community engagement and maintenance activity.
ExternalDNS supports both in-tree providers and webhook-based external providers. This architectural decision reduces maintenance burden and allows community-driven provider development. The repository documents numerous webhook providers including implementations for Hetzner, DigitalOcean, Infoblox, and many others, with over 40 known external providers listed.
Configuration of ExternalDNS is flexible, supporting both command-line flags and environment variables for all settings. Users can customize TTL values through annotations, manage internal hostnames, and configure ownership tracking through txt-prefix settings. The controller can run as a control loop within a cluster or locally for testing purposes. ExternalDNS handles special cases such as bare metal Kubernetes clusters behind NAT by supporting externalIPs lists for LoadBalancer services, enabling integration with solutions like MetalLB. The project maintains comprehensive documentation and provides tutorials for provider-specific setup, ingress controllers, and advanced configuration options.
