Overview

In ambient mode, Istio implements its features using a per-node Layer 4 (L4) proxy, and optionally a per-namespace Layer 7 (L7) proxy.

This layered approach allows you to adopt Istio in a more incremental fashion, smoothly transitioning from no mesh, to a secure L4 overlay, to full L7 processing and policy — on a per-namespace basis, as needed. Furthermore, workloads running in different Istio data plane modes interoperate seamlessly, allowing users to mix and match capabilities based on their particular needs as they change over time.

Since workload pods no longer require proxies running in sidecars in order to participate in the mesh, ambient mode is often informally referred to as “sidecar-less mesh”.

How it works

Ambient mode splits Istio’s functionality into two distinct layers. At the base, the ztunnel secure overlay handles routing and zero trust security for traffic. Above that, when needed, users can enable L7 waypoint proxies to get access to the full range of Istio features. Waypoint proxies, while heavier than the ztunnel overlay alone, still run as an ambient component of the infrastructure, requiring no modifications to application pods.

Pods and workloads using sidecar mode can co-exist within the same mesh as pods that use ambient mode. The term “ambient mesh” refers to an Istio mesh that was installed with support for ambient mode, and so can support mesh pods that use either type of data plane.

For details on the design of ambient mode, and how it interacts with the Istio control plane, see the data plane and control plane architecture documentation.

ztunnel

The ztunnel (Zero Trust tunnel) component is a purpose-built, per-node proxy that powers Istio’s ambient data plane mode.

Ztunnel is responsible for securely connecting and authenticating workloads within the mesh. The ztunnel proxy is written in Rust and is intentionally scoped to handle L3 and L4 functions such as mTLS, authentication, L4 authorization and telemetry. Ztunnel does not terminate workload HTTP traffic or parse workload HTTP headers. The ztunnel ensures L3 and L4 traffic is efficiently and securely transported to waypoint proxies, where the full suite of Istio’s L7 functionality, such as HTTP telemetry and load balancing, is implemented.

The term “secure overlay” is used to collectively describe the set of L4 networking functions implemented in an ambient mesh via the ztunnel proxy. At the transport layer, this is implemented via an HTTP CONNECT-based traffic tunneling protocol called HBONE.

Waypoint proxies

The waypoint proxy is a deployment of the Envoy proxy; the same engine that Istio uses for its sidecar data plane mode.

Waypoint proxies run outside of application pods. They are installed, upgraded, and scale independently from applications.

Some use cases of Istio in ambient mode may be addressed solely via the L4 secure overlay features, and will not need L7 features, thereby not requiring deployment of a waypoint proxy. Use cases requiring advanced traffic management and L7 networking features will require deployment of a waypoint.