Merge pull request kubernetes#122 from jhixson74/master_azure_interna…

…l_private_clusters

Azure: Internal/Private clusters enhancement doc

enhancements/installer/azure-private-internal-clusters.md

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+---
+title: Azure: Internal/Private Clusters
+authors:
+  - "@jhixson"
+reviewers:
+  - "@abhinavdahiya"
+  - "@sdodson"
+approvers:
+  - "@abhinavdahiya"
+  - "@sdodson"
+creation-date: 2019-09-10
+last-updated: 2019-10-15
+status:
+    implemented
+
+---
+
+#  azure-internal-private-clusters
+
+## Release Signoff Checklist
+
+- [x] Enhancement is `implementable`
+- [x] 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
+
+- Many of our customers require their cluster has entry points which are only
+"internal"; requirement for many disconnected environments without direct
+Internet connectivity in the VPC where OCP is installed
+- Nearly 30% of OSD clusters are internally customer-facing with VPN connectivity
+back into their corporate networks.
+- Many of our OCP 3.11 customers prefer to deploy their clusters this way
+especially for disconnected use cases where they may not always have external
+connectivity.
+- In addition to AWS, we will also need to support this for our other public
+cloud providers.
+
+## Motivation
+
+### Goals
+
+Install an OpenShift cluster on Azure as internal/private, which is only
+accessible from my internal network and not visible to the Internet.
+
+### Non-Goals
+
+- No day 2 change: a private cluster cannot become public and a public cluster
+cannot be made private
+- No additional isolation from other clusters guarantees in addition to the ones
+provided by shared VPC
+
+## Proposal
+
+- The bootstrap host will not get a public IP for SSH access
+- The gather bootstrap functionality will need to be updated to use the private
+IP
+- This affects the default ingress setup for the cluster to be internal too
+
+### Details
+
+#### Assumptions made by the installer
+
+- The installer will no longer require the user to provide the
+BaseDomainResourceGroup as no public records need to be created for the
+cluster.
+- The cluster will still require access to the internet. 
+
+#### Resources provided to the installer
+
+- Internal/Private clusters will make use of a pre-exisiting virtual network
+- No new resources should be necessary
+
+#### Installer Resources
+
+##### The installer will no longer create:
+
+- Public IP addresses
+- Public DNS records
+- Public load balancers
+- Public endpoints
+
+##### The installer will continue to create:
+
+- Private IP addresses
+- Private DNS records
+- Private load balancers
+
+#### API
+
+#### Install Config
+
+Internal vs external clusters will be determined based on the new field in
+install-config as described in the AWS internal/private clusters design doc. 
+
+#### Gather bootstrap
+
+The BootstrapIP function currently uses the
+`azurerm_public_ip.bootstrap_public_ip` resource as the IP for the
+bootstrap-host. But for internal clusters, the function will have to use the
+`azurerm_network_interface.bootstrap.private_ip_address` attribute.
+
+Using the private IP whenever the public IP is not available should be
+acceptable because all such cases will only be when the cluster is Private.
+
+#### Isolation between clusters
+
+Since we are installing to internal/private networks, isolation will not be an
+issue. 
+
+#### Known limitations
+
+- We can’t attach or manipulate network security groups to an existing subnet since it’s not in our control. This means we can’t isolate between clusters also.
+- We can’t attach DNS records to the existing VNet, so we will need to use the new Azure private DNS zones. 
+
+#### Destroy
+
+There should be no work required. For Azure, we filter on resource group. As a
+result, destroy should only delete resources that are in the resource group. 
+
+#### CI
+
+CI jobs should setup a private VNet, routing, subnets, and then run the install
+using this configuration.