# Envoy, NGINX, and WSGI

[Envoy](https://www.envoyproxy.io/), a [CNCF gradutated project](https://www.cncf.io/projects/#fws_5f44766fd58b5:~:text=Envoy),
is a reverse-proxy and load-balancer for cloud native and standalone use.
Big projects like
[istio](https://istio.io/),
[linkerd](https://linkerd.io/), and
[contour](https://projectcontour.io/) are built on top of envoy.
Above anything, performance is probably the greatest concern when it comes to reverse-proxies and load-balancers.
Informal benchmarks, such as [this](https://www.loggly.com/blog/benchmarking-5-popular-load-balancers-nginx-haproxy-envoy-traefik-and-alb/),
often show that the performance of envoy is on par with big players like [HAProxy](http://www.haproxy.org/) and
[nginx](https://www.nginx.com/).
Benchmarking envoy is [hard](https://www.envoyproxy.io/docs/envoy/latest/faq/performance/how_to_benchmark_envoy).
However, it is still a good choice if its [design goals](https://www.envoyproxy.io/docs/envoy/latest/intro/what_is_envoy) suit your need.

## Installation

Envoy provides the [getenvoy](https://www.getenvoy.io/install/envoy/) installation portal, which has connections to [tetrate](https://www.tetrate.io/open-source-contributions/).
The getenvoy [installation tutorial for CentOS](https://www.getenvoy.io/install/envoy/centos/)
is, in fact, written for CentOS 7.
In the tutorial, the `yum-utils` package is first installed to make the `yum-config-manager` command available.
According to the [Fedora doc](https://docs.fedoraproject.org/en-US/Fedora/23/html/System_Administrators_Guide/sec-Managing_DNF_Repositories.html),
the `config-manager` subcommand built into `dnf` provides the same functionality as `yum-config-manager`.
Hence, on CentOS 8, it is as easy as:

dnf config-manager --add-repo https://getenvoy.io/linux/centos/tetrate-getenvoy.repo
dnf install -y getenvoy-envoy

Check the version with the following command to make sure that it agrees with the highest stable version number shown [here](https://www.envoyproxy.io/docs), i.e., the number right under *latest*.

envoy --version

# WSGI

Pronounced *whisgee* (with a hard *g*, making it sound like whiskey), [WSGI](https://wsgi.readthedocs.io/en/latest/what.html)
is a [python standard](https://www.python.org/dev/peps/pep-3333/)
describing the interaction of a backend python application with a front-facing HTTP server, which is basically an improved CGI aimed for python.

[js-sequence-diagrams](https://bramp.github.io/js-sequence-diagrams/)

client->"reverse\nproxy": HTTP
"reverse\nproxy"->"WSGI\nserver": HTTP
"WSGI\nserver"->"python\napp": wsgi

[mermaid](https://mermaid-js.github.io/mermaid/#/sequenceDiagram)

sequenceDiagram

participant client
participant gw as reverse<br/>proxy
participant man as process<br/>manager
participant wsgi as WSGI<br/>server
participant app as python<br/>app

rect rgb(240,240,240)
    Note left of client: basic
    client ->> wsgi : HTTP
    wsgi ->> app : wsgi
end

rect rgb(240,240,240)
    Note left of client: TLS termination
    client ->> gw : HTTPS
    gw ->> wsgi : HTTP
    wsgi ->> app : wsgi
end

rect rgb(240,240,240)
    Note left of client: HA
    client ->> gw : HTTPS
    gw ->> man : HTTP
    man ->> wsgi : UDS
    wsgi ->> app : wsgi
end

[PlantUML](https://plantuml.com/sequence-diagram)

@startuml

participant client
participant envoy as gw
box "WSGI server" #LightBlue
    participant circus as man
    participant "chausette/bjoem" as wsgi
end box
participant "keystone-api-server" as app

client ->> gw : HTTPS
gw ->> man : HTTP
man ->> wsgi : UDS
wsgi ->> app : wsgi

@enduml

## Installation

Create a python virtual environment first; see [Python Virtual Environment](/1c9dEuD-QoyM3J6JvwOG6Q) instructions.
I'll call it *wsgi*.

Update *pip* and install *wheel*, *six*:

pip install --upgrade pip
pip install wheel six

Install the main tools:

pip install circus chaussette bjoern

*bjoern* build failed with missing header `ev.h`.
Install `libev-devel` then rebuid `bjoern`:

sudo dnf install libev-devel
pip install bjoern