Add proposal for Async Azure Resource Creation and Deletion

docs/Makefile

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+# Copyright 2021 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+ROOT_DIR:=$(shell dirname $(realpath $(lastword $(MAKEFILE_LIST))))
+
+SOURCES := $(shell find ${ROOT_DIR} -name \*.plantuml)
+DIAGRAMS := $(SOURCES:%.plantuml=%.png)
+
+# Hosts running SELinux need :z added to volume mounts
+SELINUX_ENABLED := $(shell cat /sys/fs/selinux/enforce 2> /dev/null || echo 0)
+
+ifeq ($(SELINUX_ENABLED),1)
+  DOCKER_VOL_OPTS?=:z
+endif
+
+.PHONY: diagrams
+diagrams: $(DIAGRAMS)
+
+%.png: %.plantuml
+	docker run \
+		--rm \
+		--volume ${ROOT_DIR}:/workdir$(DOCKER_VOL_OPTS) \
+		--user $(shell id -u):$(shell id -g) \
+		k8s.gcr.io/cluster-api/plantuml:1.2019.6 \
+		-v /workdir/$(shell echo '$^' | sed -e 's,.*docs/,,g' )

docs/proposals/images/async-delete.plantuml

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+@startuml
+title Figure 2. Azure service async delete
+state longrunningopinprogress <<choice>>
+
+[*]     --> longrunningopinprogress : start Delete
+longrunningopinprogress --> GetResultIfDone   : long running operation\nalready in progress
+GetResultIfDone : fetch the future data from the scope
+GetResultIfDone : check if future is done
+
+GetResultIfDone --> [*] : requeue if not done
+GetResultIfDone --> UpdateStatus : done
+UpdateStatus : update the object conditions
+UpdateStatus --> [*]
+
+longrunningopinprogress --> Delete  : no long running operation\n in progress
+Delete : DELETE the resource from Azure
+Delete : wait for the operation to complete
+Delete : timeout after x seconds
+
+Delete --> ResetLongRunningState : DELETE operation completes \n before timeout
+ResetLongRunningState : set the long running operation state to nil
+ResetLongRunningState --> UpdateStatus
+
+Delete --> StoreLongRunningState : DELETE operation does not\n complete before timeout
+StoreLongRunningState: store the future in long running operation state
+StoreLongRunningState --> UpdateStatus
+
+@enduml

docs/proposals/images/async-reconcile.plantuml

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+@startuml
+title Figure 1. Azure service async reconcile
+state longrunningopinprogress <<choice>>
+
+[*]     --> longrunningopinprogress : start Reconcile
+longrunningopinprogress --> GetResultIfDone   : long running operation\nalready in progress
+GetResultIfDone : fetch the future data from the scope
+GetResultIfDone : check if future is done
+
+GetResultIfDone --> [*] : requeue if not done
+GetResultIfDone --> UpdateStatus : done
+UpdateStatus : update the resource spec and status
+UpdateStatus : update the object conditions
+UpdateStatus --> [*]
+
+longrunningopinprogress --> GetExisting  : no long running operation\n in progress
+GetExisting : GET the resource from Azure if it exists
+GetExisting --> UpdateStatus : resource exists\n no update needed
+GetExisting --> CreateOrUpdate : resource does not exist,\n create it
+GetExisting --> CreateOrUpdate : resource exists\n but needs to be updated
+
+CreateOrUpdate : PUT the resource to Azure
+CreateOrUpdate : wait for the operation to complete
+CreateOrUpdate : timeout after x seconds
+
+CreateOrUpdate --> ResetLongRunningState : PUT operation completes \n before timeout
+ResetLongRunningState : set the long running operation state to nil
+ResetLongRunningState --> UpdateStatus
+
+CreateOrUpdate --> StoreLongRunningState : PUT operation does not\n complete before timeout
+StoreLongRunningState: store the future in long running operation state
+
+StoreLongRunningState --> UpdateStatus
+
+@enduml

docs/proposals/images/azure-cluster-reconcile.plantuml

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+@startuml
+hide empty description
+title Figure 3. AzureCluster reconcile loop
+
+[*] --> ReconcileResourceGroup : start AzureCluster Reconcile with global timeout
+
+ReconcileResourceGroup --> ReconcileVNet
+ReconcileResourceGroup -> UpdateStatus : context timeout exceeded
+ReconcileResourceGroup: start with local timeout
+ReconcileResourceGroup: each Azure call has its own timeout 
+
+ReconcileVNet --> ReconcileSecurityGroups
+ReconcileVNet -> UpdateStatus : context timeout exceeded
+ReconcileVNet: start with local timeout
+ReconcileVNet: each Azure call has its own timeout
+
+ReconcileSecurityGroups --> ReconcileRoutesTables
+ReconcileSecurityGroups -> UpdateStatus : context timeout exceeded
+ReconcileSecurityGroups: start with local timeout
+ReconcileSecurityGroups: each Azure call has its own timeout
+
+ReconcileRoutesTables --> ReconcilePublicIPs
+ReconcileRoutesTables -> UpdateStatus : context timeout exceeded
+ReconcileRoutesTables: start with local timeout
+ReconcileRoutesTables: each Azure call has its own timeout
+
+ReconcilePublicIPs --> ReconcileNATGateways
+ReconcilePublicIPs -> UpdateStatus : context timeout exceeded
+ReconcilePublicIPs: start with local timeout
+ReconcilePublicIPs: each Azure call has its own timeout
+
+ReconcileNATGateways --> ReconcileSubnets
+ReconcileNATGateways -> UpdateStatus : context timeout exceeded
+ReconcileNATGateways: start with local timeout
+ReconcileNATGateways: each Azure call has its own timeout
+
+ReconcileSubnets --> ReconcileLoadBalancers
+ReconcileSubnets -> UpdateStatus : context timeout exceeded
+ReconcileSubnets: start with local timeout
+ReconcileSubnets: each Azure call has its own timeout
+
+ReconcileLoadBalancers --> UpdateStatus
+ReconcileLoadBalancers -> UpdateStatus : context timeout exceeded
+ReconcileLoadBalancers: start with local timeout
+ReconcileLoadBalancers: each Azure call has its own timeout
+
+UpdateStatus --> [*]
+UpdateStatus : store long running operation(s) future data
+UpdateStatus : update conditions
+UpdateStatus : patch resource status and spec
+
+@enduml