Documentation: NGINX as data plane

[ja20222]

NKG uses NGINX as a data plane. While the configuration aspect of the data plane is hidden behind the Gateway API resources, it is only one aspect - we also have the operational aspect as well as troubleshooting, debugging and monitoring ones.

We need to make sure our NKG users are prepared to deal with NGINX - understand how it behaves and misbehaves in the context of NKG, so that they can configure and manage NGINX with high performance and reliability.

A documentation guide will help to prepare the users. The guide will:

• Explain the minimal NGINX knowledge NKG user and point to helpful resources for learning.
• Explain how exactly NGINX is used (potentially linking to a separate architecture/how it works guide)
• Explain how NGINX operates considering the architecture and configuration by the control plane (ex. pod resources, number of configuration reloads, etc.)
• Explain NGINX high levels of the generated configuration and how trouble shoot it when things don’t work.

[mpstefan]

What is missing in this story should be covered by #551