Extensibility
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.
Example
An example C++ Proxy-Wasm plugin for a filter can be found here.
To implement a Proxy-Wasm plugin for a filter:
- Implement a root context class which inherits base root context class
- Implement a stream context class which inherits the base context class.
- Override context API methods to handle corresponding initialization and stream events from host.
- Register the root context and stream context.
SDK
A detailed description of the C++ SDK can be found here.