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Design

Resources and components

This document describes the design of the Managed Upgrade Operator and the resources it uses.

The following diagram illustrates the main resources that the Managed Upgrade Operator interacts with.

Managed Upgrade Operator

The operator is primarily driven through an UpgradeConfig custom resource, which defines the version of OpenShift that the cluster should be running at.

The UpgradeConfig can be created directly on the cluster which is not managed via Hive. Also this method can be used for development/testing purposes

For OpenShift Dedicated cluster you should not create UpgradeConfig directly. The process for scheduling an upgrade is automated and achieved using the upgrade_policies API.

The process for creating upgrade-policy is documented in SOPs.

Custom Resource Definitions

UpgradeConfig

Configuration

The UpgradeConfig Custom Resource Definition (CRD) defines the version of OpenShift Container Platform that the cluster should be upgraded to, when conditions allow.

For the purpose of upgrading a cluster, an UpgradeConfig resource must be configured with the following properties:

Item Definition Example
type The cluster upgrader to use when upgrading (valid values: OSD, ARO) OSD
upgradeAt Timestamp indicating when the upgrade can commence (ISO-8601) 2020-05-01T12:00:00Z
PDBForceDrainTimeout Duration in minutes that a PDB-blocked node is allowed to drain before a drain is forced 120
desired.version The desired OCP release to upgrade to 4.4.6
desired.channel The channel the Cluster Version Operator should be using to validate update versions fast-4.4
desired.image The image digest that CVO should use to upgrade cluster. quay.io/openshift-release-dev/ocp-release@sha256:783a2c963f35ccab38e82e6a8c7fa954c3a4551e07d2f43c06098828dd986ed4
capacityReservation If extra worker node(s) are needed during the upgrade to hold the customer workload true

A populated UpgradeConfig example is presented below:

apiVersion: upgrade.managed.openshift.io/v1alpha1
kind: UpgradeConfig
metadata:
  name: managed-upgrade-config
spec:
  type: "OSD"
  upgradeAt: "2020-06-20T12:00:00Z"
  PDBForceDrainTimeout: 120
  capacityReservation: true
  desired:
    channel: "fast-4.4"
    version: "4.4.6"

The CRD is available to view in the repository.

Status

The Managed Upgrade Operator will record the history of its efforts to apply the desired upgrade within the UpgradeConfig's status section. Data within this section can be used to determine the operator's progress to apply the upgrade.

At the top level, the following fields are defined in a list, each list element representing a unique cluster version:

Item Definition Example
version The cluster version that the operator events related to 4.4.6
startTime The ISO-8601 timestamp at which the upgrade commenced. 2020-07-05T01:35:36Z
completeTime The ISO-8601 timestamp at which the upgrade completed. 2020-07-05T01:35:36Z
phase The current phase of the upgrade's application New, Pending, Upgrading, Upgraded, Failed, Unknown
conditions Data pertaining to a particular upgrade step that the operator performs -

Within conditions, each upgrade step can record its own individual status. These conditions are similar to Pod conditions, but relate to upgrade steps.

Item Definition Example
type The type of upgrade step being performed PreHealthCheck
startTime The ISO-8601 timestamp at which the step commenced. 2020-07-05T01:35:36Z
completeTime The ISO-8601 timestamp at which the step completed. 2020-07-05T01:35:36Z
lastProbeTime The last time this step's condition was last probed 2020-07-05T01:35:36Z
lastTransitionTime The last time this step transitioend from one status to another 2020-07-05T01:35:36Z
message Human-readable details indicating details about the transition PreHealthCheck succeed
reason Human-readable details about why the transition has occurred Cluster has critical alerts
status Status of the condition True, False, Unknown

A fully-populated example of an UpgradeConfig status is included below:

  status:
    history:
    - phase: Upgraded
      version: 4.3.26              
      startTime: "2020-07-05T01:35:36Z"      
      completeTime: "2020-07-05T03:15:37Z"                                                     
      conditions:            
      - completeTime: "2020-07-05T03:15:36Z"
        lastProbeTime: "2020-07-05T03:15:36Z"
        lastTransitionTime: "2020-07-05T03:15:36Z"                                             
        message: ScaleUpExtraNodes succeed                                                     
        reason: ScaleUpExtraNodes succeed  
        startTime: "2020-07-05T03:15:36Z"
        status: "True"                   
        type: ScaleUpExtraNodes
      - completeTime: "2020-07-05T03:15:36Z"
        lastProbeTime: "2020-07-05T03:15:36Z"
        lastTransitionTime: "2020-07-05T03:15:36Z"                                             
        message: PreHealthCheck succeed                                                        
        reason: PreHealthCheck succeed                                                         
        startTime: "2020-07-05T03:15:36Z"                                                      
        status: "True"                   
        type: PreHealthCheck

Config Managers

The managed-upgrade-operator provides a configurable mechanism for retrieving and storing an UpgradeConfig Custom Resource that can be reconciled against by the UpgradeConfig controller.

For more information, see the dedicated section on this topic: UpgradeConfig Managers

Controllers

The managed upgrade operator provided upgrade process revolves around multiple Controllers. Alongside the above mentioned UpgradeConfig controller, the NodeKeeper controller works simultaneously in an upgrade process towards the state of nodes in the cluster.

The NodeKeeper controller keeps a track of the upgrading worker nodes during an upgrade and seeks to ensure their timely and eventual upgrade.

If an upgrading worker node is experiencing difficulty draining due to conditions such as Pod Disruption Budgets or stuck finalizers, the NodeKeeper controller will perform remediation strategies to ensure the node's eventual drain and subsequent upgrade continuation. The NodeKeeper controller will flag through metrics any worker node that continue to unsuccessfully drain in spite of the remediation strategies.

Upgrade Process

Cluster Upgrader

The steps performed by the Managed Upgrade Operator are carried out by implementations of the clusterUpgrader interface.

Each clusterUpgrader implementation must define an ordered series of UpgradeSteps, which represent idempotent conditions that together form the procedure of a managed cluster upgrade.

UpgradeSteps are homogeneous functions of code that carry out a part of the upgrade process. If the step has completed, it will return true. If the step has not completed, it will return false. If the step has failed, it will return an false and an accompanying error.

When actively performing a cluster upgrade, the operator will follow the process below during each iteration of the controller reconcile loop:

  • Get the first step in the ordered list.
  • Execute the step.
    • If the step returns true indicating it has successfully completed, move to the next step.
    • If the step returns false indicating it has not successfully completed, the operator will stop processing steps and restart on the next reconcile loop.
    • If the step returns an error, the error will be passed back up to the controller and logged, and the current step execution will be restarted on the next reconcile loop.

Steps should generally be idempotent in nature; if they have already run and completed during an upgrade, they should return true for subsequent calls and not attempt to re-perform the same action. An example of this is the ControlPlaneMaintWindow step to create a maintenance window.

This overall process of executing Upgrade Steps is illustrated below.

Managed Upgrade Operator

To define a new custom procedure for performing a cluster upgrade, a developer should:

  • Create a new implementation of the clusterUpgrader that defines a unique order of UpgradeSteps.
  • Implement any missing or new UpgradeSteps that need to be performed.

Ready to upgrade criteria

The UpgradeConfig controller will only attempt to perform an upgrade if the current system time is later than the upgradeAt timestamp specified in the UpgradeConfig CR.

For example:

upgradeAt time Current time Commence Upgrade?
2020-05-01 12:00:00 2020-05-01 11:50:00 No, it is not yet 12:00
2020-05-01 12:00:00 2020-05-01 12:15:00 Yes, an upgrade can commence

Specific clusterUpgraders can incorporate additional ready-to-upgrade criteria in their UpgradeCluster() implementation. For example, the osdClusterUpgrader incorporates the ability to fail an upgrade if it has not commenced a control plane upgrade within a configurable time window.

Validating upgrade versions

The following checks are made against the desired version in the UpgradeConfig to assert that it is a valid version to upgrade to.

  • The version to upgrade to is greater than the currently-installed version (rollbacks are not supported)
  • The Cluster Version Operator reports it as an available version to upgrade to.