Deprecate the sidecar (non-GD) mode in DB-less

[mflendrich]

Is there an existing issue for this?

• [X] I have searched the existing issues

Problem Statement

#702 has added Gateway Discovery that has been offered as a (default on) alternative in the deploy manifests and in the kong/ingress Helm chart.

3.0 is good time to officially discontinue the legacy (sidecar) model.

Proposed Solution

• Make kong/ingress the only recommended way of installing KIC in the documentation.
• Let the documentation state that the sidecar model is no longer supported as of 3.0.
• Explicitly disallow the sidecar model in the Kong/kong Helm chart if KIC >= 3.0.

Additional information

This only refers to DB-less.

Acceptance Criteria

• [ ] When following instructions in docs to install DB-mode, the user ends up with a DB mode installation that has GD enabled (and not the sidecar model)

[mflendrich]

~Blocked by https://github.com/Kong/kubernetes-ingress-controller/issues/4698~

[mflendrich]

~Tracking DB mode GD in https://github.com/Kong/kubernetes-ingress-controller/issues/4751~

[rainest]

Explicitly disallow the sidecar model in the Kong/kong Helm chart if KIC >= 3.0.

This isn't really possible as such. The sidecar model is the only way kong can deploy both the controller and proxy with a single release. ingress is automating some of the work to create multiple releases.

We can't really set up kong to support both sidecar and separate Deployments without making the settings and templates both harder to understand, so I would strongly recommend against it. Supporting only one mode of operation simplifies usage and development, so unless we have a strong reason to support sidecar mode still, we should instead make kong only support multiple Deployments, and then work on figuring out a migration plan for releases created with ingress so that we're no longer stuck with the limitations inherent to umbrella charts.

There shouldn't be any reason to need to use the sidecar model AFAIK, and keeping it if so wouldn't buy us anything other than consistency with earlier versions for consistency's sake.

[pmalek]

Make kong/ingress the only recommended way of installing KIC in the documentation.

README.md already points users to use the ingress chart.

[mflendrich]

Blocked by https://github.com/Kong/charts/issues/921