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feat: implement scheduling mechanism for prebuilds (#18126)

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Closes https://github.com/coder/internal/issues/312
Depends on https://github.com/coder/terraform-provider-coder/pull/408

This PR adds support for defining an **autoscaling block** for
prebuilds, allowing number of desired instances to scale dynamically
based on a schedule.

Example usage:
```
data "coder_workspace_preset" "us-nix" {
  ...
  
  prebuilds = {
    instances = 0                  # default to 0 instances
    
    scheduling = {
      timezone = "UTC"             # a single timezone is used for simplicity
      
      # Scale to 3 instances during the work week
      schedule {
        cron = "* 8-18 * * 1-5"    # from 8AM–6:59PM, Mon–Fri, UTC
        instances = 3              # scale to 3 instances
      }
      
      # Scale to 1 instance on Saturdays for urgent support queries
      schedule {
        cron = "* 8-14 * * 6"      # from 8AM–2:59PM, Sat, UTC
        instances = 1              # scale to 1 instance
      }
    }
  }
}
```

### Behavior
- Multiple `schedule` blocks per `prebuilds` block are supported.
- If the current time matches any defined autoscaling schedule, the
corresponding number of instances is used.
- If no schedule matches, the **default instance count**
(`prebuilds.instances`) is used as a fallback.

### Why
This feature allows prebuild instance capacity to adapt to predictable
usage patterns, such as:
- Scaling up during business hours or high-demand periods
- Reducing capacity during off-hours to save resources

### Cron specification
The cron specification is interpreted as a **continuous time range.**

For example, the expression:

```
* 9-18 * * 1-5
```

is intended to represent a continuous range from **09:00 to 18:59**,
Monday through Friday.

However, due to minor implementation imprecision, it is currently
interpreted as a range from **08:59:00 to 18:58:59**, Monday through
Friday.

This slight discrepancy arises because the evaluation is based on
whether a specific **point in time** falls within the range, using the
`github.com/coder/coder/v2/coderd/schedule/cron` library, which performs
per-minute matching rather than strict range evaluation.

---------

Co-authored-by: Danny Kopping <danny@coder.com>
This commit is contained in:
Yevhenii Shcherbina
2025-06-19 11:08:48 -04:00
committed by GitHub
parent 511fd09582
commit 0f6ca55238
38 changed files with 2528 additions and 871 deletions
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8
coderd/database/models.go
View File

@ -3410,6 +3410,7 @@ type TemplateVersionPreset struct {
DesiredInstances sql.NullInt32 `db:"desired_instances" json:"desired_instances"`
InvalidateAfterSecs sql.NullInt32 `db:"invalidate_after_secs" json:"invalidate_after_secs"`
PrebuildStatus PrebuildStatus `db:"prebuild_status" json:"prebuild_status"`
SchedulingTimezone string `db:"scheduling_timezone" json:"scheduling_timezone"`
}
type TemplateVersionPresetParameter struct {
@ -3419,6 +3420,13 @@ type TemplateVersionPresetParameter struct {
Value string `db:"value" json:"value"`
}
type TemplateVersionPresetPrebuildSchedule struct {
ID uuid.UUID `db:"id" json:"id"`
PresetID uuid.UUID `db:"preset_id" json:"preset_id"`
CronExpression string `db:"cron_expression" json:"cron_expression"`
DesiredInstances int32 `db:"desired_instances" json:"desired_instances"`
}
type TemplateVersionTable struct {
ID uuid.UUID `db:"id" json:"id"`
TemplateID uuid.NullUUID `db:"template_id" json:"template_id"`