WebAssembly is a sandboxing technology which can be used to extend the Istio proxy (Envoy). The Proxy-Wasm sandbox API replaces Mixer as the primary extension mechanism in Istio.

WebAssembly sandbox goals:

  • Efficiency - An extension adds low latency, CPU, and memory overhead.
  • Function - An extension can enforce policy, collect telemetry, and perform payload mutations.
  • Isolation - A programming error or crash in one plugin doesn’t affect other plugins.
  • Configuration - The plugins are configured using an API that is consistent with other Istio APIs. An extension can be configured dynamically.
  • Operator - An extension can be canaried and deployed as log-only, fail-open or fail-close.
  • Extension developer - The plugin can be written in several programming languages.

This video talk is an introduction about architecture of WebAssembly integration.

High-level architecture

Istio extensions (Proxy-Wasm plugins) have several components:

  • Filter Service Provider Interface (SPI) for building Proxy-Wasm plugins for filters.
  • Sandbox V8 Wasm Runtime embedded in Envoy.
  • Host APIs for headers, trailers and metadata.
  • Call out APIs for gRPC and HTTP calls.
  • Stats and Logging APIs for metrics and monitoring.
Extending Istio/Envoy
Extending Istio/Envoy


An example C++ Proxy-Wasm plugin for a filter can be found here. You can follow this guide to implement a Wasm extension with C++.


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