data "coder_workspace_preset" "us-nix" {  ...    prebuilds = {    instances = 0                  # default to 0 instances        autoscaling = {      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

Multipleschedule blocks perprebuilds block are supported.
If the current time matches any defined autoscaling schedule, the corresponding number of instances is used.
If no schedule matches, thedefault 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 acontinuous time range.

For example, the expression:

* 9-18 * * 1-5

is intended to represent a continuous range from09:00 to 18:59, Monday through Friday.

However, due to minor implementation imprecision, it is currently interpreted as a range from08:59:00 to 18:58:59, Monday through Friday.

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

github-actionsbot assignedevgeniy-scherbina

May 30, 2025

evgeniy-scherbina force-pushed theyevhenii/prebuilds-autoscaling-mechanism branch from606894f toff0e813Compare

May 30, 2025 12:25

evgeniy-scherbina changed the title~~Implement autoscaling mechanism for prebuilds~~feat: implement autoscaling mechanism for prebuilds

May 30, 2025

evgeniy-scherbina force-pushed theyevhenii/prebuilds-autoscaling-mechanism branch 5 times, most recently from9af5e02 tobcfbb04Compare

June 6, 2025 19:53

evgeniy-scherbina force-pushed theyevhenii/prebuilds-autoscaling-mechanism branch 4 times, most recently from3a25178 toe0d1de7Compare

June 11, 2025 19:05

feat: implement autoscaling mechanism for prebuilds

47cb6fc

evgeniy-scherbina force-pushed theyevhenii/prebuilds-autoscaling-mechanism branch from80e52ee to47cb6fcCompare

June 12, 2025 19:08

evgeniy-scherbina marked this pull request as ready for review

June 12, 2025 19:45

evgeniy-scherbina requested review fromspikecurtis andjohnstcn ascode owners

June 12, 2025 19:45

evgeniy-scherbina mentioned this pull request

Jun 12, 2025

feat: add autoscaling configuration for prebuildscoder/terraform-provider-coder#408

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dannykopping requested changes

Jun 13, 2025

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coderd/database/dbgen/dbgen.go

		})
		require.NoError(t, err, "insert preset")
		return preset
		}

		func PresetPrebuildSchedule(t testing.TB, db database.Store, seed database.InsertPresetPrebuildScheduleParams) database.TemplateVersionPresetPrebuildSchedule {

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dannykoppingJun 13, 2025

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Typicallydbgen help funcs define default values whenseed is a zero value. Can you add those please?

coderd/database/dbgen/dbgen.go

		CronExpression: seed.CronExpression,
		Instances: seed.Instances,
		})
		require.NoError(t, err, "insert preset")

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dannykoppingJun 13, 2025

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Suggested change

	require.NoError(t,err,"insert preset")
	require.NoError(t,err,"insert preset prebuild schedule")

coderd/database/migrations/000335_add_autoscaling_to_presets.up.sql Outdated

		@@ -0,0 +1,12 @@
		-- Add autoscaling_timezone column to template_version_presets table
		ALTER TABLE template_version_presets
		ADD COLUMN autoscaling_timezone TEXT DEFAULT 'UTC' NOT NULL;

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dannykoppingJun 13, 2025

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Why do we need a default here, if the provider is not defining a default?

coderd/database/migrations/000335_add_autoscaling_to_presets.up.sql Outdated

		id UUID PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
		preset_id UUID NOT NULL,
		cron_expression TEXT NOT NULL,
		instances INTEGER NOT NULL,

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dannykoppingJun 13, 2025

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Nit: to matchtemplate_version_presets' definition.

Suggested change

	instancesINTEGERNOT NULL,
	desired_instancesINTEGERNOT NULL,

coderd/database/queries/presets.sql

		@@ -69,3 +83,6 @@ SELECT tvp.*, tv.template_id, tv.organization_id FROM
		template_version_presets tvp
		INNER JOIN template_versions tv ON tvp.template_version_id = tv.id
		WHERE tvp.id = @preset_id;

		-- name: GetPresetPrebuildSchedules :many
		SELECT * FROM template_version_preset_prebuild_schedules;

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dannykoppingJun 13, 2025

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Don't we want to constrain this to schedules that areonly associated to active template versions?

coderd/prebuilds/preset_snapshot.go

		}

		// Look for a schedule whose cron expression matches the provided time
		for _, schedule := range p.PrebuildSchedules {

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dannykoppingJun 13, 2025

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This is my main reason for blocking this review. We have to deal with conflicting schedules here, explicitly.

If we take this current approach, and conflicting schedules are evaluated in different orders on each reconciliation loop, then that will cause a lot of churn by spinning up and down prebuilds if those schedules' instance counts differ.

coderd/prebuilds/preset_snapshot_test.go Outdated

Comment on lines 1069 to 1070

		spec: "* 9-18 * * 1-5",
		at: mustParseTime(t, time.RFC1123, "Mon, 02 Jun 2025 8:59:00 UTC"),

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dannykoppingJun 13, 2025•
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This would violate my expectations as an operator. If the autoscaling schedule is going to kick in 1m before my given cron expression, that would be quite surprising and unintuitive.

I think we should try address this shortcoming if we can.
Edit: I looked into the implementation and made some suggestions.

This test could also be more explicit about why8:59:00 matches9-18.

coderd/schedule/cron/cron.go OutdatedShow resolvedHide resolved

go.mod

Comment on lines +533 to +534


		//replace github.com/coder/terraform-provider-coder/v2 => /home/coder/terraform-provider-coder

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Suggested change


	//replacegithub.com/coder/terraform-provider-coder/v2=>/home/coder/terraform-provider-coder

go.mod

		@@ -101,7 +101,8 @@ require (
		github.com/coder/quartz v0.2.1
		github.com/coder/retry v1.5.1
		github.com/coder/serpent v0.10.0
		github.com/coder/terraform-provider-coder/v2 v2.5.3
		// TODO: release new provider version and set it here
		github.com/coder/terraform-provider-coder/v2 v2.5.4-0.20250611180058-d61894db8492

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dannykoppingJun 13, 2025

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Remember TODO.

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spikecurtis commentedJun 13, 2025

The "continuous time" interpretation of the crontab makes it, I guess, relatively simple to specify spans that start and end on the hour, but consider attempting to program a span like 7:45am - 9:10am. You'd need 3 spans

45-59 7 * * 1-5
* 8 * * 1-5
0-10 9 * * 1-5

Are we just kind of assuming that operators likely only want hourly precision?

evgeniy-scherbinaand others added5 commits

June 13, 2025 10:22

fix: precision issue with is-within-range function

0f4d521

Co-authored-by: Danny Kopping <danny@coder.com>

test: fix is-within-range test

b957eb6

test: minor fixes in is-within-range test

de920b8

test: fix tests failed due to is-within-range function

5d31b43

fix: migration numbers

b3130a8

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evgeniy-scherbina commentedMay 30, 2025• editedLoading Uh oh!There was an error while loading.Please reload this page.

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Behavior

Why

Cron specification

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dannykoppingJun 13, 2025• editedLoading Uh oh!There was an error while loading.Please reload this page.

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spikecurtis commentedJun 13, 2025

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evgeniy-scherbina commentedMay 30, 2025•
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dannykoppingJun 13, 2025•
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