feat: implement graceful, modifiable UDS Core CoreDNS overrides

[justinthelaw]

Description

Implements an alternative CoreDNS override that relies on UDS Core's base service mesh, Istio. Uses the admin and tenant ingress gateways as the rewrite targets to gracefully handle ungraceful Docker restarts/stops, where host.k3d.internal fails. Also handles the case of integrating and routing to potential/future alternative service meshes via CoreDNS (e.g., kong). Another added benefit is the end-user's ability to add further rewrites based on additional or alternative gateways, domains, subdomains, services and/or virtual services.

Related Issue

Fixes #99

Type of change

• New feature (non-breaking change which adds functionality)

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide Steps followed

[justinthelaw]

Local tests were performed to ensure the override works with UDS Core (slim-dev):

1. Use uds zarf tools kubectl get configmap -n kube-system coredns-custom -o yaml >> coredns-overrides.yaml on the locally created uds-k3d cluster on this PR's branch
2. Apply (w/o resourceVersion, uid, and creationTimestamp) the coredns-overrides.yaml to a fresh deployment of k3d-core-slim-dev from upstream UDS Core
3. Re-cycle the CoreDNS deployment
4. Visited the sso.uds.dev and keycloak.admin.uds.dev URLs in a browser

EDIT: let me know if this is something you want me to automate into a CI test.

[justinthelaw]

@rjferguson21 @mjnagel I sort of modified things based on a combination of your guys' comments. Please let me know if there's more you'd like me to change. Thank you!

[justinthelaw]

@rjferguson21 @mjnagel turns out, the wrong indent type was used, thanks @rjferguson21 for pointing it out! Everything is in working order now. feel free to run things without and with an override to see how they work.

[justinthelaw]

Final output without providing the override at deployment:

apiVersion: v1
data:
  uds.override: |
    rewrite stop {
      name regex (.*\.admin\.uds\.dev) admin-ingressgateway.istio-admin-gateway.svc.cluster.local answer auto
    }
    rewrite stop {
      name regex (.*\.uds\.dev) tenant-ingressgateway.istio-tenant-gateway.svc.cluster.local answer auto
    }
    rewrite stop {
      name regex (.*\.uds\.dev) host.k3d.internal answer auto
    }
kind: ConfigMap
metadata:
  annotations:
    meta.helm.sh/release-name: uds-dev-stack
    meta.helm.sh/release-namespace: uds-dev-stack
  labels:
    app.kubernetes.io/managed-by: Helm
  name: coredns-custom
  namespace: kube-system

Final output when supplying the override within docs/DNS.md:

apiVersion: v1
data:
  uds.override: |
    rewrite stop {
      name regex (.*\.uds\.dev) host.k3d.internal answer auto
    }
kind: ConfigMap
metadata:
  annotations:
    meta.helm.sh/release-name: uds-dev-stack
    meta.helm.sh/release-namespace: uds-dev-stack
  labels:
    app.kubernetes.io/managed-by: Helm
  name: coredns-custom
  namespace: kube-system