Consul by HashiCorp

Modern service proxies provide high-level service routing, authentication, telemetry, and more for microservice and cloud environments. Envoy is a popular and feature-rich proxy that is often used on its own. Consul integrates with Envoy to simplify its configuration.

Proxies require a rich set of configuration to operate since backend addresses, frontend listeners, routes, filters, telemetry shipping, and more must all be configured. Further, a modern infrastructure contains many proxies, often one proxy per service as proxies are deployed in a "sidecar" model next to a service. Therefore, a primary challenge of proxies is the configuration sprawl and orchestration.

Proxies form what is referred to as the "data plane": the pathway which data travels for network connections. Above this is the "control plane" which provides the rules and configuration for the data plane. Proxies typically integrate with outside solutions to provide the control plane. For example, Envoy integrates with Consul to dynamically populate service backend addresses.

Consul is a control plane solution. The service catalog serves as a registry for services and their addresses and can be used to route traffic for proxies. The Connect feature of Consul provides the TLS certificates and service access graph, but still requires a proxy to exist in the data path. As a control plane, Consul integrates with many data plane solutions including Envoy, HAProxy, Nginx, and more.

The Consul Envoy integration is currently the primary way to utilize advanced layer 7 features provided by Consul. In addition to Envoy, Consul enables third party proxies to integrate with Connect and provide the data plane with Consul operating as the control plane.

Proxies provide excellent solutions to layer 7 concerns such as path-based routing, tracing and telemetry, and more. By supporting a pluggable data plane model, the right proxy can be deployed as needed. For performance-critical applications or those that utilize layer 7 functionality, Envoy can be used. For non-performance critical layer 4 applications, you can use Consul's built-in proxy for convenience.

For some applications that may require hardware, a hardware load balancer such as an F5 appliance may be deployed. Consul encourages this use of the right proxy for the scenario and treats hardware load balancers as swappable components that can be run alongside other proxies, assuming they integrate with the necessary APIs for Connect.