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Ensure support for backing up resources based on multiple labels

Abstract

As of today Velero supports filtering of resources based on single label selector per backup. It is desired that Velero support backing up of resources based on multiple labels (OR logic).

Note: This solution is required because kubernetes label selectors only allow AND logic of labels.

Background

Currently, Velero's Backup/Restore API has a spec field LabelSelector which helps in filtering of resources based on a single label value per backup/restore request. For instance, if the user specifies the Backup.Spec.LabelSelector as data-protection-app: true, Velero will grab all the resources that possess this label and perform the backup operation on them. The LabelSelector field does not accept more than one labels, and thus if the user want to take backup for resources consisting of a label from a set of labels (label1 OR label2 OR label3) then the user needs to create multiple backups per label rule. It would be really useful if Velero Backup API could respect a set of labels (OR Rule) for a single backup request.

Goals

Enable support for backing up resources based on multiple labels (OR Logic) in a single backup config.
Enable support for restoring resources based on multiple labels (OR Logic) in a single restore config.

Use Case/Scenario

Let's say as a Velero user you want to take a backup of secrets, but all these secrets do not have one single consistent label on them. We want to take backup of secrets having any one label in app=gdpr, app=wpa and app=ccpa. Here we would have to create 3 instances of backup for each label rule. This can become cumbersome at scale.

High-Level Design

Addition of `OrLabelSelectors` spec to Velero Backup/Restore API

For Velero to back up resources if they consist of any one label from a set of labels, we would like to add a new spec field OrLabelSelectors which would enable user to specify them. The Velero backup would somewhat look like:

apiVersion: velero.io/v1
kind: Backup
metadata:
  name: backup-101
  namespace: openshift-adp
spec:
  includedNamespaces:
  - test
  storageLocation: velero-sample-1
  ttl: 720h0m0s
  orLabelSelectors:
  - matchLabels:
      app=gdpr
  - matchLabels:
      app=wpa
  - matchLabels:
      app=ccpa

Note: This approach will not be changing any current behavior related to Backup API spec LabelSelector. Rather we propose that the label in LabelSelector spec and labels in OrLabelSelectors should be treated as different Velero functionalities. Both these fields will be treated as separate Velero Backup API specs. If LabelSelector (singular) is present then just match that label. And if OrLabelSelectors is present then match to any label in the set specified by the user. For backup case, if both the LabelSelector and OrLabelSelectors are specified (we do not anticipate this as a real world use-case) then the OrLabelSelectors will take precedence, LabelSelector will only be used to filter only when OrLabelSelectors is not specified by the user. This helps to keep both spec behaviour independent and not confuse the users. This way we preserve the existing Velero behaviour and implement the new functionality in a much cleaner way. For instance, let's take a look the following cases:

Only LabelSelector specified: Velero will create a backup with resources matching label app=protect-db

apiVersion: velero.io/v1
kind: Backup
metadata:
  name: backup-101
  namespace: openshift-adp
spec:
  includedNamespaces:
  - test
  storageLocation: velero-sample-1
  ttl: 720h0m0s
  labelSelector:
  - matchLabels:
      app=gdpr

Only OrLabelSelectors specified: Velero will create a backup with resources matching any label from set {app=gdpr, app=wpa, app=ccpa}

apiVersion: velero.io/v1
kind: Backup
metadata:
  name: backup-101
  namespace: openshift-adp
spec:
  includedNamespaces:
  - test
  storageLocation: velero-sample-1
  ttl: 720h0m0s
  orLabelSelectors:
  - matchLabels:
      app=gdpr
  - matchLabels:
      app=wpa
  - matchLabels:
      app=ccpa

Similar implementation will be done for the Restore API as well.

Detailed Design

With the Introduction of OrLabelSelectors the BackupSpec and RestoreSpec will look like:

BackupSpec:

type BackupSpec struct {
[...]
// OrLabelSelectors is a set of []metav1.LabelSelector to filter with
// when adding individual objects to the backup. Resources matching any one
// label from the set of labels will be added to the backup. If empty
// or nil, all objects are included. Optional.
// +optional
OrLabelSelectors []\*metav1.LabelSelector
[...]
}

RestoreSpec:

type RestoreSpec struct {
[...]
// OrLabelSelectors is a set of []metav1.LabelSelector to filter with
// when restoring objects from the backup. Resources matching any one
// label from the set of labels will be restored from the backup. If empty
// or nil, all objects are included from the backup. Optional.
// +optional
OrLabelSelectors []\*metav1.LabelSelector
[...]
}

The logic to collect resources to be backed up for a particular backup will be updated in the backup/item_collector.go around here.

And for filtering the resources to be restored, the changes will go here

Note:

This feature will not be exposed via Velero CLI.

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