Which protocol does Envoy primarily use for service-to-service communication?

Envoy primarily uses HTTP/2 for service-to-service communication because it provides several advantages over previous versions of HTTP. HTTP/2 introduces features like multiplexing, which allows multiple streams of data to be sent simultaneously over a single TCP connection. This reduces latency and improves the overall efficiency of data transport. Additionally, HTTP/2 supports header compression, further optimizing the performance and reducing the overhead compared to HTTP/1.1. The use of these advanced features allows Envoy to manage service communications effectively in a microservices architecture, where responsiveness and resource utilization are critical.

While TCP is a foundational protocol for transporting data, it does not encompass the application-level capabilities that HTTP/2 provides. HTTP/1.1, although still in use, lacks the performance enhancements that HTTP/2 brings, particularly in handling concurrent connections and stream multiplexing. WebSocket is primarily focused on establishing persistent connections and bi-directional data transfer, which may not align with the full scope of service-to-service communication needs addressed by Envoy using HTTP/2. These factors collectively underline why HTTP/2 is the preferred choice for Envoy in facilitating efficient and effective service interactions.