The Ambassador Edge Stack Architecture

The Ambassador Edge Stack is a Control Plane

The Ambassador Edge Stack is a specialized control plane for Envoy Proxy. In this architecture, the Ambassador Edge Stack translates configuration (in the form of Kubernetes Custom Resources) to Envoy configuration. All actual traffic is directly handled by the high-performance Envoy Proxy.

Details

1. The service owner defines configuration in Kubernetes manifests.
2. When the manifest is applied to the cluster, the Kubernetes API notifies the Ambassador Edge Stack of the change.
3. The Ambassador Edge Stack parses the change and transforms the configuration into a semantic intermediate representation. Envoy configuration is generated from this IR.
4. The new configuration is passed to Envoy via the gRPC-based Aggregated Discovery Service (ADS) API.
5. Traffic flows through the reconfigured Envoy, without dropping any connections.

Scaling and Availability

The Ambassador Edge Stack relies on Kubernetes for scaling, high availability, and persistence. All Ambassador Edge Stack configuration is stored directly in Kubernetes; there is no database. The Ambassador Edge Stack is packaged as a single container that contains both the control plane and an Envoy Proxy instance. By default, the Ambassador Edge Stack is deployed as a Kubernetes deployment and can be scaled and managed like any other Kubernetes deployment.

Stateless Architecture

By design, the Ambassador Edge Stack is an entirely stateless architecture. Each individual Ambassador Edge Stack instance operates independently of other instances. These Ambassador Edge Stack instances rely on Kubernetes to coordinate the configuration between different the Ambassador instances. This enables the Ambassador Edge Stack to sidestep the need to engineer a safe, highly available centralized control plane (and if you don't think that this is hard, check out Jepsen). By contrast, other control plane architectures rely on a single centralized control plane to manage multiple instances of the data plane. This means that these control plane architectures must engineer resilience and availability into their central control plane.

Envoy Proxy

The Ambassador Edge Stack closely tracks Envoy Proxy releases. A stable branch of Envoy Proxy is maintained that enables the team to cherry-pick specific fixes into the Ambassador Edge Stack.