Envoy Proxy is an open-source proxy server (it fulfils the same role as HAProxy, Nginx, and similar tools). Envoy is highly flexible and configurable via its plugin architecture.
Envoy was developed at Lyft and open-sourced in 2016. From the outset it was intended to have a role in both observability and in mitigating and avoiding load related issues.
Envoy always has a static configuration file, which can be YAML or JSON (in this workshop we will be using
envoy.yaml as the configuration file). Envoy supports having most of its configuration supplied dynamically via
a control plane - almost everything except the configuration for the control plane itself - so things can be
changed centrally without needing to restart Envoy. However, we won't be using
dynamic configuration here, for simplicity's sake and to make the configurations clear.
Some terminology you should know is downstream and upstream.
Downstreams are basically clients, which initiate connections to servers (upstreams).
However, the use of the terms downstream and upstream is preferred, as many upstreams are also downstreams of something else: the concept should always be seen as specific to the context of a given Envoy configuration.
In this workshop we will only have one layer of downstreams and upstreams in each demo, so it will be clear which services/clusters are meant.
Envoy configuration can be very complex, which is mainly a consequence of Envoy being flexible. Listeners, filters, and clusters are the core elements of Envoy configuration and are worth an introduction.
Listeners listen for connections on some port. When a connection is received, it will be processed through
a chain of filters, which can modify requests in various ways.
Most Envoy configuration relates to filter configuration, and most of the demos in this workshop are primarily about configuring filters (with the exception of circuitbreaking, which is done at the cluster level, and Envoy overload management).
Clusters manage sets of upstreams, plus optional loadbalancing configurations.
Envoy is designed to be extensible. Envoy is written in C++, as are many of its plugins. However, extensions (specifically, HTTP filters) exist to permit plugins to be written in other languages, such as Go and Lua.
When running any demo in this workshop you will find Envoy's admin interface and status page at http://localhost:9901.
See documentation on the admin interface here.
You can try this out by running the plain Envoy non-demo.
When running most of the demos in this workshop you will find Envoy's exported metrics at http://localhost:9901/stats/prometheus. It can be useful to explore them here so you know what's available for graphing in Prometheus or Grafana.
You can also try this out by running the plain Envoy non-demo.