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feat: implement scheduling mechanism for prebuilds (#18126)

Browse Source 
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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114
coderd/schedule/cron/cron_test.go
View File

@ -163,6 +163,120 @@ func Test_Weekly(t *testing.T) {
}
}
func TestIsWithinRange(t *testing.T) {
t.Parallel()
testCases := []struct {
name string
spec string
at time.Time
expectedWithinRange bool
expectedError string
}{
// "* 9-18 * * 1-5" should be interpreted as a continuous time range from 09:00:00 to 18:59:59, Monday through Friday
{
name: "Right before the start of the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 8:59:59 UTC"),
expectedWithinRange: false,
},
{
name: "Start of the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 9:00:00 UTC"),
expectedWithinRange: true,
},
{
name: "9:01 AM - One minute after the start of the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 9:01:00 UTC"),
expectedWithinRange: true,
},
{
name: "2PM - The middle of the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 14:00:00 UTC"),
expectedWithinRange: true,
},
{
name: "6PM - One hour before the end of the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 18:00:00 UTC"),
expectedWithinRange: true,
},
{
name: "End of the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 18:59:59 UTC"),
expectedWithinRange: true,
},
{
name: "Right after the end of the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 19:00:00 UTC"),
expectedWithinRange: false,
},
{
name: "7:01PM - One minute after the end of the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 19:01:00 UTC"),
expectedWithinRange: false,
},
{
name: "2AM - Significantly outside the time range",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 02:00:00 UTC"),
expectedWithinRange: false,
},
{
name: "Outside the day range #1",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Sat, 07 Jun 2025 14:00:00 UTC"),
expectedWithinRange: false,
},
{
name: "Outside the day range #2",
spec: "* 9-18 * * 1-5",
at: mustParseTime(t, time.RFC1123, "Sun, 08 Jun 2025 14:00:00 UTC"),
expectedWithinRange: false,
},
{
name: "Check that Sunday is supported with value 0",
spec: "* 9-18 * * 0",
at: mustParseTime(t, time.RFC1123, "Sun, 08 Jun 2025 14:00:00 UTC"),
expectedWithinRange: true,
},
{
name: "Check that value 7 is rejected as out of range",
spec: "* 9-18 * * 7",
at: mustParseTime(t, time.RFC1123, "Sun, 08 Jun 2025 14:00:00 UTC"),
expectedError: "end of range (7) above maximum (6): 7",
},
}
for _, testCase := range testCases {
testCase := testCase
t.Run(testCase.name, func(t *testing.T) {
t.Parallel()
sched, err := cron.Weekly(testCase.spec)
if testCase.expectedError != "" {
require.Error(t, err)
require.Contains(t, err.Error(), testCase.expectedError)
return
}
require.NoError(t, err)
withinRange := sched.IsWithinRange(testCase.at)
require.Equal(t, testCase.expectedWithinRange, withinRange)
})
}
}
func mustParseTime(t *testing.T, layout, value string) time.Time {
t.Helper()
parsedTime, err := time.Parse(layout, value)
require.NoError(t, err)
return parsedTime
}
func mustLocation(t *testing.T, s string) *time.Location {
t.Helper()
loc, err := time.LoadLocation(s)