Multi-cluster communication

Linkerd can connect Kubernetes services across cluster boundaries in a way that is secure, fully transparent to the application, and independent of network topology. This multi-cluster capability is designed to provide:

  1. A unified trust domain. The identity of source and destination workloads are validated at every step, both in and across cluster boundaries.
  2. Separate failure domains. Failure of a cluster allows the remaining clusters to function.
  3. Support for heterogeneous networks. Since clusters can span clouds, VPCs, on-premises data centers, and combinations thereof, Linkerd does not introduce any L3/L4 requirements other than gateway connectivity.
  4. A unified model alongside in-cluster communication. The same observability, reliability, and security features that Linkerd provides for in-cluster communication extend to cross-cluster communication.

Just as with in-cluster connections, Linkerd’s cross-cluster connections are transparent to the application code. Regardless of whether that communication happens within a cluster, across clusters within a datacenter or VPC, or across the public Internet, Linkerd will establish a connection between clusters that’s encrypted and authenticated on both sides with mTLS.

How it works

Linkerd's multi-cluster support works by “mirroring” service information between clusters. Because remote services are represented as Kubernetes services, the full observability, security and routing features of Linkerd apply uniformly to both in-cluster and cluster-calls, and the application does not need to distinguish between those situations.

Overview
Overview

Linkerd's multi-cluster functionality is implemented by two components: a service mirror and a gateway. The service mirror component watches a target cluster for updates to services and mirrors those service updates locally on a source cluster. This provides visibility into the service names of the target cluster so that applications can address them directly. The multi-cluster gateway component provides target clusters a way to receive requests from source clusters. (This allows Linkerd to support hierarchical networks.)

Once these components are installed, Kubernetes Service resources that match a label selector can be exported to other clusters.

Ready to get started? See the getting started with multi-cluster guide for a walkthrough.

Further reading