argo-cd/docs/user-guide/sync_windows.md

Sync Windows

Sync windows are configurable windows of time where syncs will either be blocked or allowed. These are defined by a kind, which can be either allow or deny, a schedule in cron format and a duration along with one or more of either applications, namespaces and clusters. If more than one option is specified, by default, the enabled options will be OR-ed. If you want to AND the options, you can tick the Use AND operator option. Wildcards are supported.

Relationship between Sync Windows and Applications

The relationship between Sync Windows and Application resources is many-to-many. This means that an Application resource may be affected by multiple Sync Windows, and that a single Sync Window definition may apply to multiple Application resources.

The relationship between Sync Window and Application is established as part of the definition of Sync Window. Sync Window definition includes a section defining the Application resources to which it applies. There are three mechanisms for selecting the Application resources to which a Sync Window applies:

• By name of Application resource
• By cluster into which resources are installed by Application resource. This is specified by Application.spec.destination.name and .server fields
• By namespace into which resources are installed by Application resource. This is specified by Application.spec.destination.namespace field.

All three mechanisms allow usage of wildcards. The mechanisms are not mutually exclusive, and all three of them can be used in single Sync Window definition.

When multiple selection mechanisms are used, they are effectively ORed, meaning that if any of the selector selects the Application, then the Application is affected by the Sync Window.

Effect of Sync Windows

These windows affect the running of both manual and automated syncs but allow an override for manual syncs which is useful if you are only interested in preventing automated syncs or if you need to temporarily override a window to perform a sync.

The windows work in the following way:

• If there are no windows matching an application then all syncs are allowed.
• If there are any allow windows matching an application then syncs will only be allowed when there is an active allow window.
• If there are any deny windows matching an application then all syncs will be denied when the deny windows are active.
• If there is an active matching allow and an active matching deny then syncs will be denied as deny windows override allow windows.

Sync Overrun

The syncOverrun option allows automatic syncs that are already running to continue even when they transition out of their allowed window. This is particularly useful when you want to prevent new syncs from starting during maintenance windows but don't want to interrupt syncs that are already in progress.

Sync overrun can be configured on both allow and deny windows:

Deny Window Overrun

When syncOverrun is enabled on a deny window:

• Syncs that started before the deny window became active will be allowed to complete
• New syncs will still be blocked during the deny window
• All active deny windows must have syncOverrun enabled for the overrun to be allowed

Allow Window Overrun

When syncOverrun is enabled on an allow window:

• Syncs that started during the allow window will be allowed to continue even after the window ends
• This is useful for long-running syncs that may extend beyond the scheduled window
• All inactive allow windows must have syncOverrun enabled for the overrun to be allowed
• The sync can continue as long as:
  • No deny window without overrun becomes active
  • If a deny window becomes active, it must also have syncOverrun enabled

Transition Scenarios

Here are some common scenarios and their behavior:

1. No window → Deny with overrun: Sync continues (deny supports overrun, sync was permitted when it started)
2. No window → Deny without overrun: Sync is blocked (deny doesn't support overrun)
3. Allow with overrun → Deny with overrun: Sync continues (both windows support overrun)
4. Allow with overrun → Deny without overrun: Sync is blocked (deny doesn't support overrun)
5. Allow without overrun → Deny with overrun: Sync is allowed (deny supports overrun, sync was permitted when it started)
6. Allow without overrun → Deny without overrun: Sync is blocked (neither supports overrun)
7. Allow with overrun → Allow ends: Sync continues (overrun enabled on original allow window)
8. Multiple allows with overrun → All end: Sync continues (all allow windows have overrun)
9. Multiple allows, one without overrun → All end: Sync is blocked (not all allow windows have overrun)

The UI and the CLI will both display the state of the sync windows. The UI has a panel which will display different colours depending on the state. The colours are as follows. Red: sync denied, Orange: manual allowed and Green: sync allowed.

To display the sync state using the CLI:

argocd app get APP

Which will return the sync state and any matching windows.

Name:               guestbook
Project:            default
Server:             in-cluster
Namespace:          default
URL:                http://localhost:8080/applications/guestbook
Repo:               https://github.com/argoproj/argocd-example-apps.git
Target:
Path:               guestbook
SyncWindow:         Sync Denied
Assigned Windows:   deny:0 2 * * *:1h,allow:0 2 3 3 3:1h
Sync Policy:        Automated
Sync Status:        Synced to  (5c2d89b)
Health Status:      Healthy

Windows can be created using the CLI:

argocd proj windows add PROJECT \
    --kind allow \
    --schedule "0 22 * * *" \
    --duration 1h \
    --applications "*"

To create a window with sync overrun enabled (allowing in-progress syncs to continue):

# Allow window with overrun - syncs can continue after window ends
argocd proj windows add PROJECT \
    --kind allow \
    --schedule "0 9 * * *" \
    --duration 8h \
    --applications "*" \
    --sync-overrun

# Deny window with overrun - in-progress syncs can continue during deny window
argocd proj windows add PROJECT \
    --kind deny \
    --schedule "0 22 * * *" \
    --duration 1h \
    --applications "*" \
    --sync-overrun

Alternatively, they can be created directly in the AppProject manifest:

apiVersion: argoproj.io/v1alpha1
kind: AppProject
metadata:
  name: default
spec:
  syncWindows:
  - kind: allow
    schedule: '10 1 * * *'
    duration: 1h
    applications:
    - '*-prod'
    manualSync: true
  - kind: allow
    schedule: '0 9 * * *'
    duration: 8h
    applications:
    - '*'
    syncOverrun: true  # Allow syncs to continue after window ends
  - kind: deny
    schedule: '0 22 * * *'
    timeZone: "Europe/Amsterdam"
    duration: 1h
    namespaces:
    - default
    syncOverrun: true  # Allow in-progress syncs to continue during deny window
  - kind: allow
    schedule: '0 23 * * *'
    duration: 1h
    clusters:
    - in-cluster
    - cluster1

In order to perform a sync when syncs are being prevented by a window, you can configure the window to allow manual syncs using the CLI, UI or directly in the AppProject manifest:

argocd proj windows enable-manual-sync PROJECT ID

To disable:

argocd proj windows disable-manual-sync PROJECT ID

Similarly, you can enable or disable sync overrun for existing windows:

argocd proj windows enable-sync-overrun PROJECT ID

To disable:

argocd proj windows disable-sync-overrun PROJECT ID

Windows can be listed using the CLI or viewed in the UI:

argocd proj windows list PROJECT

ID  STATUS    KIND   SCHEDULE    DURATION  APPLICATIONS  NAMESPACES  CLUSTERS  MANUALSYNC  SYNCOVERRUN  TIMEZONE  USEANDOPERATOR
0   Active    allow  * * * * *   1h        -             -           prod1     Disabled    Disabled     UTC       Disabled
1   Inactive  deny   * * * * 1   3h        -             default     -         Disabled    Enabled      UTC       Disabled
2   Inactive  allow  1 2 * * *   1h        prod-*        -           -         Enabled     Disabled     UTC       Disabled
3   Active    deny   * * * * *   1h        -             default     -         Disabled    Disabled     UTC       Disabled

All fields of a window can be updated using either the CLI or UI. The applications, namespaces and clusters fields require the update to contain all of the required values. For example if updating the namespaces field and it already contains default and kube-system then the new value would have to include those in the list.

argocd proj windows update PROJECT ID --namespaces default,kube-system,prod1