consul/docs/v2-architecture/service-mesh/README.md

V2 Service Mesh Architecture

In Consul 1.16 and 1.17 releases, Consul's service mesh has been rewritten to use the controller architecture and the resource APIs.

At a high level, the service mesh consists of resources and controllers living in three groups: catalog, mesh, and auth.

The controllers in each groups are responsible for producing an output that may then be used by other controllers.

-> Note: This diagram is valid as of Consul 1.17. It may change in the future releases.

Catalog controllers

Catalog controllers are responsible for reconciling resources in the catalog API group.

1. FailoverPolicy controller validates FailoverPolicy resource has valid service references and updating the status the FailoverPolicy resource with the result.
2. WorkloadHealth controller takes in workloads and any relevant health statuses and updates the status of a workload with the combined health status.
3. NodeHealth controller takes in nodes and any relevant health statuses and updates the status of a node with the combined health status.
4. ServiceEndpoints controller generates a ServiceEndpoints object that is name-aligned with a service and contains workload addresses and ports that constitute a service.

Mesh Controllers

1. ProxyConfiguration controller generates a ComputedProxyConfiguration resource that is name-aligned with a workload. ComputedProxyConfiguration contains all merged ProxyConfiguration resources that apply to a specific workload.
2. Routes controller generates a ComputedRoutes resource that is name-aligned with a service. It contains merged configuration from all xRoutes objects as well as FailoverPolicy and DestinationPolicy.
3. ExplicitDestinations controller generates a ComputedExplicitDestinations resource that is name-aligned with a workload. It contains merged Destinations resources that apply to a specific workload.
4. SidecarProxy controller takes in the results of the previous three controllers as well as some user-provided resources and generates ProxyStateTemplate resource which serves as the representation of Envoy configuration for sidecar proxies.
5. XDSController takes in ProxyStateTemplate resources, fills in missing endpoints references as well as certificates and CA roots and sends them over to another component that sends this information over to Envoy.

Auth Controllers

1. TrafficPermissions controller generates ComputedTrafficPermissions resource that is name-aligned with WorkloadIdentity. This computed resource contains all traffic permissions that apply to a specific workload identity.