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

```bash
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:

```bash
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):

```bash
# 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:

```yaml
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:

```bash
argocd proj windows enable-manual-sync PROJECT ID
```

To disable:

```bash
argocd proj windows disable-manual-sync PROJECT ID
```

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

```bash
argocd proj windows enable-sync-overrun PROJECT ID
```

To disable:

```bash
argocd proj windows disable-sync-overrun PROJECT ID
```

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

```bash
argocd proj windows list PROJECT
```

```bash
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. 

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