Kuryr Kubernetes Loadbalancers Reconciliation Design

The purpose of this document is to define the design decision behind
the OpenStack resources reconciliation. A ServiceReconciliationHandler
is added to the Kuryr Controller pipeline which manages the OpenStack
service events.

Change-Id: Ib28708fa726137469913f1b83e679a905490b218

doc/source/devref/index.rst

@@ -45,6 +45,7 @@ Design documents
    kuryr_kubernetes_versions
    network_policy
    updating_pod_resources_api
+   lbaas_reconciliation_design.rst
 
 
 Indices and tables

doc/source/devref/lbaas_reconciliation_design.rst

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+..
+      This work is licensed under a Creative Commons Attribution 3.0 Unported
+      License.
+
+      http://creativecommons.org/licenses/by/3.0/legalcode
+
+      Convention for heading levels in Neutron devref:
+      =======  Heading 0 (reserved for the title in a document)
+      -------  Heading 1
+      ~~~~~~~  Heading 2
+      +++++++  Heading 3
+      '''''''  Heading 4
+      (Avoid deeper levels because they do not render well.)
+
+====================================================
+Kuryr Kubernetes Loadbalancers Reconciliation Design
+====================================================
+
+Purpose
+-------
+The purpose of this document is to present an approach for implementing the
+design of the Kuryr Kubernetes Loadbalancers reconciliation.
+
+Overview
+--------
+
+Currently, if the OpenStack loadbalancer is manually deleted or removed,
+due to the Octavia loadbalancer being stuck on PENDING_UPDATE, Kuryr does
+not detect this event neither does it recreate the OpenStack resources.
+Hence, it is necessary to monitor changes in OpenStack resources in order
+to  ensure that the information on the "spec" section of the CRD is represented
+on OpenStack, and then  update the "status" of the CRD with the recovered or
+created OpenStack resources.
+
+
+
+Proposed Solution
+-----------------
+
+The implementation requires detecting changes in OpenStack loadbalancers
+and reconciling with KuryrKubernetes CRD. The OpenStack resources are pooled
+occasionally to check for the information on the spec data. If some resources
+on OpenStack are missing, we remove them from the associated KuryrLoadBalancer
+CRD status, so that the KuryrLoadBalancerHandler react to it (re-executes the
+on_present function) and by executing the sync_lbaas_member function reconciles
+it (i.e., recovering the existing resources, recreating the missing ones).
+
+Diagram describing Loadbalancers Reconciliation Design
+
+.. image:: ../../images/lbaas_recon_design.png
+   :alt: Lbaas reconciliation design
+   :align: center
+   :width: 100%
+
+
+
+Kuryr Controller Impact
+~~~~~~~~~~~~~~~~~~~~~~~
+
+We shall implement a reconciliation event which checks the OpenStack loadbalancers
+for missing spec data. Since the KuryrLoadBalancerHandler watches the
+KuryrLoadBalancers CRD, we shall implement the reconciliation event on the handler.
+If there is a missing information on the OpenStack resource, the
+KuryrLoadBalancerHandler which has the KuryLoadBalancer CRD, sets the status field
+to `empty`. This triggers the KuryrLoadBalancerHandler which then reconciles the
+OpenStack resources by calling the LoadBalancer Driver.
+
+Diagram describing Loadbalancers Reconciliation Design
+
+.. image:: ../../images/lbaas_recon_flow.png
+   :alt: Lbaas reconciliation flow design
+   :align: center
+   :width: 100%
+
+
+
+
+
+