Closescoder/internal#312
Depends oncoder/terraform-provider-coder#408

This PR adds support for defining anautoscaling 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

• 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.