syncset.md

SyncSet

• Overview
• SyncSet Object Definition
  • How to use applyBehavior
  • Resource Parameters
    • fromCDLabel Custom Function
  • Example of SyncSet use
• SelectorSyncSet Object Definition
• Ordering
• Diagnosing SyncSet Failures
• Changing ResourceApplyMode

Overview

SyncSet and SelectorSyncSet objects facilitate resource management (create, update, delete, patch) in hive-managed clusters.

To use SyncSet objects to manage resources, you must create them in the same namespace as the ClusterDeployment resource that they manage. If you want to manage resources in clusters that match a specific label use SelectorSyncSet instead. These objects apply changes to clusters in any namespace that match the clusterDeploymentSelector that you set.

With both SyncSets and SelectorSyncSets, the individual resources and patches are reapplied when 2 hours have passed since their last reconciliation (by default) or if their contents are updated in the SyncSet or SelectorSyncSets.

The default syncSetReapplyInterval can be overridden by specifying a string duration within the hiveconfig such as syncSetReapplyInterval: "1h" for a one hour reapply interval.

SyncSet Object Definition

SyncSets may contain a list of resource object definitions to create and a list of patches to be applied to existing objects.

---
apiVersion: hive.openshift.io/v1
kind: SyncSet
metadata:
  name: mygroup
spec:
  clusterDeploymentRefs:
  - name: ClusterName

  resourceApplyMode: Upsert

  applyBehavior: CreateOnly

  enableResourceTemplates: false

  resources:
  - apiVersion: user.openshift.io/v1
    kind: Group
    metadata:
      name: mygroup
    users:
    - myuser

  patches:
  - kind: ConfigMap
    apiVersion: v1
    name: foo
    namespace: default
    patch: |-
      { "data": { "foo": "new-bar" } }
    patchType: merge

  secretMappings:
  - sourceRef:
      name: ad-bind-password
      namespace: default
    targetRef:
      name: ad-bind-password
      namespace: openshift-config

Field	Usage
clusterDeploymentRefs	List of ClusterDeployment names in the current namespace which the SyncSet will apply to.
resourceApplyMode	Defaults to "Upsert", which indicates that objects will be created and updated to match the SyncSet. Existing SyncSet resources that are not listed in the SyncSet are not deleted. Specify "Sync" to allow deleting existing objects that were previously in the resources list. This includes deleting all resources when the entire SyncSet is deleted.
applyBehavior	One of Apply (the default), CreateOnly, CreateOrUpdate. Affects how the controller computes the patch to apply to resources and secretMappings (but not patches). More details below.
enableResourceTemplates	If true, special use of golang's text/templates is allowed in resources. More details below.
resources	A list of resource object definitions. Resources will be created in the referenced clusters.
patches	A list of patches to apply to existing resources in the referenced clusters. You can include any valid cluster object type in the list. By default, the patch applyMode value is "AlwaysApply", which applies the patch every 2 hours.
secretMappings	A list of secret mappings. The secrets will be copied from the existing sources to the target resources in the referenced clusters

How to use applyBehavior

The applyBehavior setting affects how the controller computes and applies resources and secretMappings to the target cluster. The default, Apply, causes us to use kubectl apply, which uses the kubectl.kubernetes.io/last-applied-configuration annotation to decide whether fields absent from the syncset resource should be deleted or ignored if they are present on the target object. This is a complex topic, but in summary:

• Apply (the default): Asserts the kubectl.kubernetes.io/last-applied-configuration annotation on the target object, and uses it on subsequent reconciles.
• CreateOrUpdate: If the object is initially absent, it is created without the kubectl.kubernetes.io/last-applied-configuration annotation; and hive will not add the annotation. However, if the annotation is added some other way (e.g. the user runs kubectl apply on the object), hive will not remove it; and subsequent syncs will honor it. The behavior here is quirky:
  • Hive will always assert the presence/value of all fields in the syncset resource.
  • If the last-applied-configuration annotation is absent, hive will never delete fields.
  • If the annotation is present, the behavior is the same as Apply -- i.e. fields present in the annotation but absent from the syncset resource will be removed.
• CreateOnly: If initially absent, the object is created (without the kubectl.kubernetes.io/last-applied-configuration annotation). If the object is already present, it is ignored.

As a rule of thumb:

• If you want users of the spoke cluster to be able to edit the object and have their changes persist, use applyBehavior: CreateOnly.
• If you want to assert the exact version of the object in your [Selector]SyncSet, reverting any changes or additions made externally, use applyBehavior: Apply (or omit applyBehavior to get this behavior as the default).
• Since the behavior of CreateOrUpdate differs based on factors outside of your control -- i.e. whether the user adds/removes the kubectl.kubernetes.io/last-applied-configuration annotation from the target object -- this applyBehavior should probably be avoided. (If you come up with a good use case for it, please open an issue and tell us about it!)

This can present a special conundrum when you want to create a resource with certain attributes that should be "sticky", but allow updates elsewhere. In such cases, you may wish to combine resources and patches:

• Create your [Selector]SyncSet with applyBehavior: CreateOnly
• Include a resources entry with the initial version of the object.
• Include patches to assert the fields whose values you wish to be "sticky" (i.e. revert if they are edited/removed externally).

It is safe to put these into the same [Selector]SyncSet because:

• patches in a given [Selector]SyncSet are applied after resources.
• applyBehavior only applies to resources and secretMappings -- it does not affect patches.

Resource Parameters

By setting spec.enableResourceTemplates: true, it is possible to use golang text/template-isms in spec.resources[] values. Note, however, that there is no "dot" (data object) so the out-of-the-box functionality won't convey a lot of power. This feature exists to expose custom functions, described below.

Note:

• Templates are only honored on resource values. They are ignored for keys.
• Templates are only honored on values whose schema type is string. (This is because the embedded resource must be valid JSON before it is parsed; and templates can't be recognized as any other valid JSON type.)
• Errors parsing or processing the template will cause the SyncSet to fail and will be bubbled up in the ClusterSync status as usual.
• Templates are only supported on spec.resources[], not on patches or secretMappings.

fromCDLabel Custom Function

With enableResourceTemplates on, including a string like

{{ fromCDLabel "any.clusterdeployment/label-key" }}

in a resource will cause hive to substitute it with the value of that label from the ClusterDeployment owning the [Selector]SyncSet being processed. For example:

---
  enableResourceTemplates  : true

  resources:
  - apiVersion: v1
    kind: ConfigMap
    metadata:
      name: mycm
      namespace: myns
    data:
      platform: the platform is {{ fromCDLabel "hive.openshift.io/cluster-platform" }}

...might result in the following ConfigMap on the spoke cluster:

apiVersion: v1
kind: ConfigMap
metadata:
  name: mycm
  namespace: myns
data:
  platform: the platform is gcp

If the ClusterDeployment has no labels, or if there is no label with the specified key, the empty string is substituted.

Example of SyncSet use

In this example you can change the replicaset of a deployment running on top of a Hive managed OpenShift cluster.

• Get the required information of the deployment

$ oc get deployment <deployment name> -o yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  labels:
    app: sise
  name: sise-deploy
  namespace: default
spec:
  replicas: 2
  xxxxxxx

• Create the SyncSet object in the cluster deployment namespace in Hive managed cluster as mentioned below.

oc create -f <syncset_file.yaml> -n <namespace>

SyncSet File:

apiVersion: hive.openshift.io/v1
kind: SyncSet
metadata:
  name: sise-deploy-syncset
spec:
  clusterDeploymentRefs:
  - name: <cluster name>

  patches:
  - kind: Deployment
    apiVersion: extensions/v1beta1
    name: sise-deploy
    namespace: default
    patch: |-
      { "spec": { "replicas": 3 } }
    patchType: strategic

• To see the syncset status, run as below.

oc get clustersync <clusterdeployment name> -o yaml

SelectorSyncSet Object Definition

SelectorSyncSet functions identically to SyncSet but is applied to clusters matching clusterDeploymentSelector in any namespace.

---
apiVersion: hive.openshift.io/v1
kind: SelectorSyncSet
metadata:
  name: mygroup
spec:
  resources:
  - apiVersion: user.openshift.io/v1
    kind: Group
    metadata:
      name: mygroup
    users:
    - abutcher
  clusterDeploymentSelector:
    matchLabels:
      cluster-group: abutcher

Field	Usage
clusterDeploymentSelector	A key/value label pair which selects matching ClusterDeployments in any namespace.

Ordering

Hive will process [Selector]SyncSets and their resources in the following order:

1. SyncSets are processed first.
   1. Any necessary deletions are processed first. The order in which deletions are processed is not guaranteed.
   2. SyncSets are processed in alpha order by SyncSet name. Resources within a SyncSet are processed in the order in which they are supplied in the SyncSet.
2. SelectorSyncSets are processed next.
   1. Any necessary deletions are processed first. The order in which deletions are processed is not guaranteed.
   2. SelectorSyncSets are processed in alpha order by SelectorSyncSet name. Resources within a SelectorSyncSet are processed in the order in which they are supplied in the SelectorSyncSet.

Within a given [Selector]SyncSet, sections are processed in the following order:

1. resources
2. secretMappings
3. patches

Diagnosing SyncSet Failures

To find the status of the syncset, check the cluster deployment's ClusterSync object in the cluster deployment namespace. Every cluster deployment has an associated ClusterSync object that records status within ClusterSync.Status.SyncSets.

oc get clustersync -n <namespace>

To see details, run as below.

oc get clustersync <clusterdeployment name> -o yaml

All (Selector)SyncSets for a given ClusterDeployment are handled by a single replica of the hive-clustersync StatefulSet. The replica pods are named hive-clustersync-N where N is an integer such that 0 <= N < #replicas. ClusterSync.Status.ControlledByReplica indicates which replica is responsible for (the CD associated with) the ClusterSync. Use this to determine which replica's pod logs to examine when debugging syncset operations. For example:

$ REPLICA=`oc get clustersync -n <namespace> <clusterdeployment name> -o json | jq -r .status.controlledByReplica`
$ oc logs -n hive hive-clustersync-$REPLICA | grep <clusterdeployment name>

Note: This value is only set/updated when the cluster is installed, reachable, and not deleted.

Note: This value indicates the replica that most recently handled the ClusterSync. If the hive-clustersync statefulset is scaled up or down, the controlling replica can change, potentially causing logs to be spread across multiple pods.

Changing ResourceApplyMode

Changing the resourceApplyMode from "Sync" to "Upsert" will remove SyncSet resources tracked for deletion within the corresponding ClusterSync object. It is possible that the ClusterSync controller could process a resource removal and a resourceApplyMode change simultaneously and when this occurs resources no longer tracked in the SyncSet will be orphaned rather than deleted.

Likewise, changing the resourceApplyMode from "Upsert" to "Sync" will add SyncSet resources to resources tracked for deletion within the corresponding ClusterSync object. When the ClusterSync controller processes a resource removal and a resourceApplyMode change simultaneously, resources removed will be orphaned rather than deleted.