Adds initial ExternalDNS Operator Enhancement Proposal

This commit contains the original externalDNS operator enhancement
proposal create by Daneyon Hansen as a part of
openshift#456 (which was closed due
to inactivity).

enhancements/ingress/externaldns-operator.md

@@ -0,0 +1,261 @@
+---
+title: externaldns-operator
+authors:
+  - "@danehans"
+reviewers:
+  - "@Miciah"
+  - "@knobunc"
+  - "@frobware"
+  - "@sgreene570"
+approvers:
+  - "@knobunc"
+creation-date: 2020-08-26
+last-updated: 2020-08-26
+status: implementable
+---
+# ExternalDNS Operator
+
+## Table of Contents
+
+<!-- toc -->
+- [Release Signoff Checklist](#release-signoff-checklist)
+- [Summary](#summary)
+- [Motivation](#motivation)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+- [Proposal](#proposal)
+  - [User Stories](#user-stories)
+  - [Implementation Details](#implementation-details)
+  - [Risks and Mitigations](#risks-and-mitigations)
+- [Design Details](#design-details)
+  - [Open Questions](#open-questions)
+  - [Test Plan](#test-plan)
+  - [Graduation Criteria](#graduation-criteria)
+  - [Upgrade and Downgrade Strategy](#upgradedowngrade-strategy)
+  - [Version Skew Strategy](#version-skew-strategy)
+- [Implementation History](#implementation-history)
+- [Drawbacks](#drawbacks)
+- [Alternatives](#alternatives)
+- [Infrastructure Needed](#infrastructure-needed)
+<!-- /toc -->
+
+## Release Signoff Checklist
+
+- [X] Enhancement is `implementable`
+- [ ] Design details are appropriately documented from clear requirements
+- [ ] Test plan is defined
+- [ ] Graduation criteria for dev preview, tech preview, GA
+- [ ] User-facing documentation is created in [openshift-docs](https://github.com/openshift/openshift-docs/)
+
+## Summary
+
+This enhancement proposal is for adding an operator to manage
+[ExternalDNS](https://github.com/kubernetes-sigs/external-dns). ExternalDNS has been chosen for managing external DNS
+requirements of OpenShift clusters. Initially, the operator will focus on managing external DNS record(s) of OpenShift
+[Routes](https://github.com/openshift/api/blob/master/route/v1/types.go). The operator will have its own CRD that will
+initially expose limited configuration capabilities. Existing operators will be used to guide the design of the
+ExternalDNS Operator. Tooling will be included to make it easy to build, run, test, etc. the operator for OpenShift.
+
+## Motivation
+
+The [operator pattern](https://kubernetes.io/docs/concepts/extend-kubernetes/operator/) is generally accepted, and the
+benefits of operators to OpenShift are well-known.  This enhancement proposal aims to bring the benefits of operators to
+ExternalDNS. ExternalDNS is a controller that will manage external DNS records. As with other platform components,
+ExternalDNS requires an operator to provide lifecycle management of the component.
+
+### Goals
+
+* Explore the use of an operator for managing ExternalDNS.
+* Create patterns, libraries and tooling so that ExternalDNS is of high quality, consistent in its API
+surface (common fields on CRDs, consistent labeling of created resources, etc.), yet is easy to build.
+* Build an operator that is suitable for production use of ExternalDNS.
+* Support the [CRD source](https://github.com/kubernetes-sigs/external-dns/tree/master/docs/contributing/crd-source) and
+ExternalDNS [providers](https://github.com/kubernetes-sigs/external-dns/tree/master/provider) relevant to OpenShift.
+
+### Non-Goals
+
+* Replace the functionality of existing operators. __Note:__ The ExternalDNS Operator intends to replace external DNS
+management provided by existing components, i.e.
+[Ingress Operator](https://github.com/openshift/cluster-ingress-operator) in the long-term.
+* Create an operator that only works with Kubernetes clusters.
+* To support all ExternalDNS [sources](https://github.com/kubernetes-sigs/external-dns/tree/master/source) and 
+[providers](https://github.com/kubernetes-sigs/external-dns/tree/master/provider).
+
+## Proposal
+
+The proposal is based on experience gathered and work accomplished with existing OpenShift operators.
+
+* Create a GitHub repository to host the operator source code.
+* Leverage frameworks and libraries , i.e. controller-runtime, to simplify development
+of the operator.
+* Manage dependencies through [Go Modules](https://blog.golang.org/using-go-modules).
+* Create user and developer documentation.
+* Create tooling to simplify building, running, testing, etc. the operator.
+* Create tests that reduce bugs in the code and allow for continuous integration.
+* Integrate the operator with the OpenShift toolchain, i.e. openshift/release, required
+for productization.
+* Provide manifests for deploying the operator.
+* Create tooling to simplify ExternalDNS troubleshooting. For example, add operator support to
+[must-gather](https://github.com/openshift/must-gather).
+* Integrate ExternalDNS with the OpenShift monitoring toolchain. For example, add
+[telemetry support](https://github.com/openshift/cluster-monitoring-operator) for the operator and its operand(s).
+
+The following functionality is expected as part of the operator:
+
+* Introduce a CRD used by the operator to manage ExternalDNS and its dependencies.
+* Common fields in spec that define the configuration of ExternalDNS and any dependent resources.
+* Common fields in spec that define how to deploy ExternalDNS, i.e. number of pod replicas.
+* Common fields in status that expose the current health & version information of ExternalDNS.
+* The operator will be capable of observing other resources to perform basic sequencing required for OpenShift
+integration.
+
+An example can make this easier to understand, here is what a CRD instance for ExternalDNS may look like:
+
+```yaml
+apiVersion: operator.externaldns.io/v1alpha1
+kind: externaldns
+metadata:
+  name: default
+  namespace: my-externaldns-namespace
+spec:
+  replicas: 2
+status:
+  availableReplicas: 2
+  conditions:
+  - lastTransitionTime: "2020-08-20T23:01:33Z"
+    reason: Valid
+    status: "True"
+    type: Admitted
+  - lastTransitionTime: "2020-08-20T23:07:05Z"
+    status: "True"
+    type: Available
+  - lastTransitionTime: "2020-08-20T23:07:05Z"
+    message: The deployment has Available status condition set to True
+    reason: DeploymentAvailable
+    status: "False"
+    type: DeploymentDegraded
+```
+
+This manifest creates a deployment that ensures 2 instances of ExternalDNS are always running in the cluster.
+Additional `spec` and/or `status` fields may be introduced based on requirements.
+
+* Introduce a CRD for managing DNS records that satisfies the ExternalDNS
+[CRD source](https://github.com/kubernetes-sigs/external-dns/blob/master/docs/contributing/crd-source.md). __Note:__ The
+[ingressoperator/dnsrecord](https://github.com/openshift/api/blob/master/operatoringress/v1/types.go) CRD does not meet
+ExternalDNS CRD source requirements. If the ingressoperator/dnsrecord can be refactored, use this CRD instead of
+introducing a new CRD to manage DNS records.
+* Common fields in spec that define the desired configuration of an external DNS record.
+* Common fields in status that expose the actual state of the DNS record.
+* Platform components that require external DNS will use this CRD for managing DNS records.
+
+An example can make this easier to understand, here is what a CRD instance for an external DNS record may look like:
+
+```yaml
+apiVersion: externaldns.operator.openshift.io/v1alpha1
+kind: dnsrecord
+metadata:
+  name: default
+  namespace: my-component-namespace
+spec:
+  endpoints:
+  - dnsName: foo.example.com
+    targets:
+    - 1.2.3.4
+    recordType: A
+    recordTTL: 30
+status:
+  zones:
+  - conditions:
+    - lastTransitionTime: "2020-08-26T16:24:41Z"
+      message: The DNS provider succeeded in ensuring the record
+      reason: ProviderSuccess
+      status: "False"
+      type: Failed
+    dnsZone:
+      id: <MY_PROVIDER_ZONE_ID>
+```
+
+This manifest creates a DNS A record for hostname "foo.example.com" that resolves to address "1.2.3.4" in the configured
+provider. Additional `spec` and/or `status` fields may be introduced based on requirements.
+
+__Note:__ Any API(s) introduced by this enhancement will follow the Kubernetes API
+[deprecation policy](https://kubernetes.io/docs/reference/using-api/deprecation-policy/).
+
+### User Stories [optional]
+
+#### Story 1
+
+As a developer, I need the ability to manage DNS records for OpenShift routes.
+
+#### Story 2
+
+As a cluster administrator, I need the ability use a single operator to manage external DNS requirements for all
+platform components.
+
+### Implementation Details [optional]
+
+TBD
+
+### Risks and Mitigations
+
+TBD
+
+## Design Details
+
+TBD
+
+### Open Questions [optional]
+
+1. Should the operator be created upstream to allow for community-based development and support?
+
+### Test Plan
+
+- Develop e2e, integration and unit tests.
+- Create a CI job to run tests.
+
+### Graduation Criteria
+
+##### Dev Preview -> Tech Preview
+
+- Ability to utilize the enhancement end-to-end
+- End user documentation, relative API stability
+- Sufficient test coverage
+- Gather feedback from users rather than just developers
+
+##### Tech Preview -> GA 
+
+- More testing (upgrade, downgrade, scale)
+- Sufficient time for feedback
+- Available by default
+
+##### Removing a deprecated feature
+
+N/A
+
+### Upgrade/Downgrade Strategy
+
+The operator will follow operator best practices for supporting upgrades and downgrades.
+
+### Version Skew Strategy
+
+N/A
+
+## Implementation History
+
+N/A
+
+## Drawbacks
+
+* The amount of time required to build and maintain the operator.
+* A single instance of ExternalDNS cannot manage public and private zones for the same domain, i.e.
+*.apps.my.openshift.cluster. See
+[this](https://github.com/kubernetes-sigs/external-dns/blob/master/docs/tutorials/public-private-route53.md) for
+additional details.
+
+## Alternatives
+
+Use Ingress Operator instead of ExternalDNS to manage openshift/route DNS records.
+
+## Infrastructure Needed [optional]
+
+A repo to host the operator sourcecode.