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docs(progressivesync): Proposal of Deletion strategy for progressive sync (argoproj#22843)
Signed-off-by: Kanika Rana <krana@redhat.com>
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‎docs/proposals/deletion-strategy-progressive-sync.md‎

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---
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title: Neat-enhancement-idea
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authors:
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- "@ranakan19" # Authors' github accounts here.
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sponsors:
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- TBD # List all interested parties here.
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reviewers:
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- TBD
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approvers:
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- TBD
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creation-date: 2025-04-30
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last-updated: 2025-05-01
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---
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# Deletion Strategy for Progressive Sync
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This proposal is building upon the ideas presented in https://github.com/argoproj/argo-cd/pull/14892 to introduce
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deletion strategy for progressive sync. While the original proposal laid the groundwork, this proposal extends to address
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some unanswered sections and changes implementation details.
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Introduce a new functionality of ArgoCD ProgressiveSync that will allow users to configure order
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of deletion for applicationSet's deployed applications. The deletion strategies can be:
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- AllAtOnce (current behaviour - where all applications are deleted in no particular order without waiting for an application
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to be deleted; can be the default value)
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- reverse ( delete applications in the reverse order of deployment, configured in progressiveSync. This expects the
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rollingSync field to have a specified order and implements deletion in the reverse order specified.
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Waits for one application to be fully deleted before moving onto the next application.)
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## Open Questions [optional]
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The original proposal mentions another strategy - `custom` wherein the user can provide a specific order of deletion.
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Is such a usecase needed?
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## Summary
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This feature can extend the application dependency from deployment to deletion as well. Ability to provide deletion order
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can complete the ProgressiveSync feature.
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## Motivation
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Current deletion/removal strategy which ArgoCD use works fine if there aren't any dependencies between the different applications.
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However, it does not work when there are dependencies between the applications. This was noticed when some kubernetes core services
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were deployed in specific order and to be removed in reverse order.
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### Goals
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Following goals should be achieved in order to conclude this proposal:
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1. Deletion strategy `AllAtOnce` as default value - deletes all applications at once as the current behavior of deletion.
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2. Deletion strategy `Reverse` lets applications be deleted in the reverse order of the steps configured in RollingSync strategy.
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### Non-Goals
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custom deletion strategy - this will be a separate goal if there is enough demand for it.
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## Proposal
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Ability to provide configuration related to the deletion/removal process when progressive sync is used. Implementation detail provides
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two options of introducing this field in ApplicationSet. The following use cases assumes Option 1 for the yaml file examples.
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### Use cases
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Add a list of detailed use cases this enhancement intends to take care of.
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#### AllAtOnce deletionStrategy:
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```yaml
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apiVersion: argoproj.io/v1alpha1
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kind: ApplicationSet
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metadata:
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name: pricelist
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namespace: argocd
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spec:
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generators:
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- list:
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elements:
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- srv: config
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path: applicationsets/rollingsync/apps/pricelist-config
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- srv: db
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path: applicationsets/rollingsync/apps/pricelist-db
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- srv: frontend
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path: applicationsets/rollingsync/apps/pricelist-frontend
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strategy:
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type: RollingSync
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rollingSync:
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steps:
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- matchExpressions:
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- key: pricelist-component # the "key" is based on the label (below as "pricelist-component: {{srv}}")
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operator: In
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values:
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- config
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- matchExpressions:
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- key: pricelist-component
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operator: In
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values:
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- db
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- matchExpressions:
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- key: pricelist-component
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operator: In
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values:
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- frontend
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### Deletion configuration ###
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deletionOrder: AllAtOnce # available options to be AllAtOnce/Reverse (maybe custom as well)
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### Deletion configuration ###
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template:
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metadata:
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name: 'pricelist-{{srv}}'
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labels:
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pricelist-component: '{{srv}}'
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spec:
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project: default
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syncPolicy:
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automated:
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prune: true
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selfHeal: true
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retry:
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limit: 5
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backoff:
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duration: 5s
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maxDuration: 3m0s
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factor: 2
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source:
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repoURL: https://github.com/christianh814/gitops-examples
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targetRevision: main
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path: '{{path}}'
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destination:
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server: https://kubernetes.default.svc
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namespace: pricelist
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```
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#### Reverse deletionStrategy:
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```yaml
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apiVersion: argoproj.io/v1alpha1
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kind: ApplicationSet
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metadata:
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name: pricelist
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namespace: argocd
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spec:
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generators:
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- list:
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elements:
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- srv: config
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path: applicationsets/rollingsync/apps/pricelist-config
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- srv: db
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path: applicationsets/rollingsync/apps/pricelist-db
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- srv: frontend
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path: applicationsets/rollingsync/apps/pricelist-frontend
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strategy:
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type: RollingSync
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rollingSync:
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steps:
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- matchExpressions:
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- key: pricelist-component # the "key" is based on the label (below as "pricelist-component: {{srv}}")
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operator: In
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values:
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- config
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- matchExpressions:
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- key: pricelist-component
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operator: In
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values:
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- db
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- matchExpressions:
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- key: pricelist-component
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operator: In
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values:
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- frontend
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### Deletion configuration ###
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deletionOrder: Reverse # available options to be AllAtOnce/Reverse (maybe custom as well)
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### Deletion configuration ###
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template:
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metadata:
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name: 'pricelist-{{srv}}'
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labels:
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pricelist-component: '{{srv}}'
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spec:
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project: default
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syncPolicy:
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automated:
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prune: true
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selfHeal: true
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retry:
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limit: 5
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backoff:
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duration: 5s
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maxDuration: 3m0s
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factor: 2
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source:
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repoURL: https://github.com/christianh814/gitops-examples
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targetRevision: main
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path: '{{path}}'
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destination:
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server: https://kubernetes.default.svc
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namespace: pricelist
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```
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#### If custom deletionStrategy:
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```yaml
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apiVersion: argoproj.io/v1alpha1
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kind: ApplicationSet
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metadata:
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name: pricelist
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namespace: argocd
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spec:
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generators:
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- list:
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elements:
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- srv: config
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path: applicationsets/rollingsync/apps/pricelist-config
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- srv: db
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path: applicationsets/rollingsync/apps/pricelist-db
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- srv: frontend
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path: applicationsets/rollingsync/apps/pricelist-frontend
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strategy:
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type: RollingSync
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rollingSync:
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steps:
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- matchExpressions:
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- key: pricelist-component # the "key" is based on the label (below as "pricelist-component: {{srv}}")
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operator: In
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values:
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- config
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- matchExpressions:
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- key: pricelist-component
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operator: In
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values:
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- db
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- matchExpressions:
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- key: pricelist-component
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operator: In
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values:
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- frontend
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### Deletion configuration ###
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deletionOrder: Custom # available options to be default/reverse/custom
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deletionSync:
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steps:
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- matchExpressions:
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- key: pricelist-component # the "key" is based on the label (below as "pricelist-component: {{srv}}")
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operator: In
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values:
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- config
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- matchExpressions:
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- key: pricelist-component
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operator: In
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values:
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- frontend
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- matchExpressions:
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- key: pricelist-component
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operator: In
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values:
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- db
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### Deletion configuration ###
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template:
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metadata:
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name: 'pricelist-{{srv}}'
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labels:
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pricelist-component: '{{srv}}'
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spec:
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project: default
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syncPolicy:
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automated:
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prune: true
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selfHeal: true
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retry:
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limit: 5
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backoff:
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duration: 5s
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maxDuration: 3m0s
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factor: 2
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source:
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repoURL: https://github.com/christianh814/gitops-examples
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targetRevision: main
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path: '{{path}}'
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destination:
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server: https://kubernetes.default.svc
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namespace: pricelist
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```
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### Implementation Details/Notes/Constraints [optional]
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There should be a check that correlates the deletionStrategy to ApplicationSet strategy. For example can only select reverse
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if rollingSync lists out an order of application deployment, otherwise should error out.
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It was decided to have this field within strategy (which is a field associated with progressiveSync)
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To be introduced in ApplicationSetStrategy as follows:
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```yaml
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type ApplicationSetStrategy struct {
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Type string `json:"type,omitempty" protobuf:"bytes,1,opt,name=type"`
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RollingSync *ApplicationSetRolloutStrategy `json:"rollingSync,omitempty" protobuf:"bytes,2,opt,name=rollingSync"`
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// RollingUpdate *ApplicationSetRolloutStrategy `json:"rollingUpdate,omitempty" protobuf:"bytes,3,opt,name=rollingUpdate"`
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// Add DeletionSync Strategy here
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DeletionOrder string `json:"deletionOrder,omitempty" protobuf:"bytes,4,opt,name=deletionOrder"` // takes value AllAtOnce/Reverse
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}
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```
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Looked at the following names for this field:
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1. DeletionSyncType
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2. DeletionSyncStrategy
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But decided on having DeletionOrder for the following reasons:
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1. simpler to understand - Order is straightforward and thus sets expectation to user
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2. Since it's nested within `strategy`, suffix of strategy isn't needed.
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3. Leaving room for when/if it scales to have custom deletion strategy. i.e
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```yaml
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type ApplicationSetStrategy struct {
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Type string `json:"type,omitempty" protobuf:"bytes,1,opt,name=type"`
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RollingSync *ApplicationSetRolloutStrategy `json:"rollingSync,omitempty" protobuf:"bytes,2,opt,name=rollingSync"`
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// Add DeletionSync Strategy here
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DeletionOrder string `json:"deletionOrder,omitempty" protobuf:"bytes,3,opt,name=deletionOrder"` // takes value AllAtOnce/Reverse/Custom
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DeletionSync *ApplicationSetRolloutStrategy `json:"deletionSync,omitempty" protobuf:"bytes,4,opt,name=deletionSync"`
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}
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```
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### Detailed examples
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Already covered in Use cases
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### Security Considerations
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Since no additional roles or privileges are needed to be able to delete deployed applications in a specific order,
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so no impact on the security aspects of Argo CD workloads.
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### Risks and Mitigations
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No immediate Risks to consider
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### Upgrade / Downgrade Strategy
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Introducing new fields to the ApplicationSet CRD, however, no existing fields are being changed.
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This means that a new ApplicationSet version is unnecessary, and upgrading to the new spec with added fields will be a clean operation.
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Downgrading could risk users receiving K8s API errors if they continue to try to apply the deletionStrategy field to a downgraded version of the ApplicationSet resource.
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Downgrading the controller while keeping the upgraded version of the CRD should cleanly downgrade/revert the behavior of the controller to the previous version without requiring users to adjust their existing ApplicationSet specs.
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## Drawbacks
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Slight increase in Argo CD code base complexity
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## Alternatives
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TBD

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