Improve ConfigMap docs

[rikatz]

Is this a BUG REPORT or FEATURE REQUEST? (choose one): Bug Report / Docs Improvement

As @aledbf is making his brave journey to improve Ingress Docs in #1527 (which we're really thank to!), I've been digging some undocumented / misdocumented ConfigMap directives that should be documented after the PR above is closed.

Some of those ConfigMap directives only exists in the code, as other exists also in configuration.md but there's no default value, or only the default value and no explanation, and some have both but there's no how to use them.

This is a issue of multiple PRs, and needs help from everyone (no need to know how to code in Go, but need to know what's the impact of each directive).

I'm putting them as a list, so we can 'check' each completed box/documented directive.

Undocumented directives/Missing explanation:

• allow-backend-server-header
• client-header-buffer-size
• client-header-timeout
• client-body-buffer-size
• client-body-timeout
• vts-status-zone-size
• vts-default-filter-key
• http2-max-field-size
• http2-max-header-size
• keep-alive-requests
• large-client-header-buffers
• log-format-escape-json
• ssl-ecdh-curve
• variables-hash-bucket-size
• variables-hash-max-size
• upstream-keepalive-connections
• proxy-stream-timeout
• bind-address-ipv4
• bind-address-ipv6
• forwarded-for-header
• proxy-real-ip-cidr
• ssl-ciphers - Missing the default value

Documentation improvements

• ssl-dh-param - Needs to be better documented, probably here we should reference to customization/ssl-dh-param/README.md
• http-snippet / server-snippet / location-snippet - How this works? Is this another ConfigMap?

[pieterlange]

I will try to help out here this week, thanks for coordinating

[rikatz]

@pieterlange I'll try to help you with some items here. @mrrandrade will also take a look.

[diazjf]

@rikatz @aledbf I added a PR #1747 which provides information on usage and deployment of the config-map that way we can get new users to help with the documentation.

I added all possible options and their defaults as well by looking at https://github.com/kubernetes/ingress-nginx/blob/master/internal/ingress/controller/config/config.go

For future iteration of the docs maybe we can have sections in the table which point below to the actual option and provide information about it, similar to https://github.com/kubernetes/ingress-nginx/blob/master/docs/user-guide/annotations.md

[aledbf]

Closing. Fixed in #1747

[rikatz]

I'm missing the explanation of each directive there :(

[diazjf]

@rikatz @aledbf #1752 resolves most if not all of the items in the checklist shown above. Thanks!