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>
## Summary
This PR introduces support for expiration policies in prebuilds. The TTL
(time-to-live) is retrieved from the Terraform configuration
([terraform-provider-coder
PR](https://github.com/coder/terraform-provider-coder/pull/404)):
```
prebuilds = {
instances = 2
expiration_policy {
ttl = 86400
}
}
```
**Note**: Since there is no need for precise TTL enforcement down to the
second, in this implementation expired prebuilds are handled in a single
reconciliation cycle: they are deleted, and new instances are created
only if needed to match the desired count.
## Changes
* The outcome of a reconciliation cycle is now expressed as a slice of
reconciliation actions, instead of a single aggregated action.
* Adjusted reconciliation logic to delete expired prebuilds and
guarantee that the number of desired instances is correct.
* Updated relevant data structures and methods to support expiration
policies parameters.
* Added documentation to `Prebuilt workspaces` page
* Update `terraform-provider-coder` to version 2.5.0:
https://github.com/coder/terraform-provider-coder/releases/tag/v2.5.0
Depends on: https://github.com/coder/terraform-provider-coder/pull/404
Fixes: https://github.com/coder/coder/issues/17916
Relates to https://github.com/coder/coder/issues/17432
### Part 1:
Notes:
- `GetPresetsAtFailureLimit` SQL query is added, which is similar to
`GetPresetsBackoff`, they use same CTEs: `filtered_builds`,
`time_sorted_builds`, but they are still different.
- Query is executed on every loop iteration. We can consider marking
specific preset as permanently failed as an optimization to avoid
executing query on every loop iteration. But I decided don't do it for
now.
- By default `FailureHardLimit` is set to 3.
- `FailureHardLimit` is configurable. Setting it to zero - means that
hard limit is disabled.
### Part 2
Notes:
- `PrebuildFailureLimitReached` notification is added.
- Notification is sent to template admins.
- Notification is sent only the first time, when hard limit is reached.
But it will `log.Warn` on every loop iteration.
- I introduced this enum:
```sql
CREATE TYPE prebuild_status AS ENUM (
'normal', -- Prebuilds are working as expected; this is the default, healthy state.
'hard_limited', -- Prebuilds have failed repeatedly and hit the configured hard failure limit; won't be retried anymore.
'validation_failed' -- Prebuilds failed due to a non-retryable validation error (e.g. template misconfiguration); won't be retried.
);
```
`validation_failed` not used in this PR, but I think it will be used in
next one, so I wanted to save us an extra migration.
- Notification looks like this:
<img width="472" alt="image"
src="https://github.com/user-attachments/assets/e10efea0-1790-4e7f-a65c-f94c40fced27"
/>
### Latest notification views:
<img width="463" alt="image"
src="https://github.com/user-attachments/assets/11310c58-68d1-4075-a497-f76d854633fe"
/>
<img width="725" alt="image"
src="https://github.com/user-attachments/assets/6bbfe21a-91ac-47c3-a9d1-21807bb0c53a"
/>
Closes https://github.com/coder/internal/issues/510
<details>
<summary> Refactoring Summary </summary>
### 1) `CalculateActions` Function
#### Issues Before Refactoring:
- Large function (~150 lines), making it difficult to read and maintain.
- The control flow is hard to follow due to complex conditional logic.
- The `ReconciliationActions` struct was partially initialized early,
then mutated in multiple places, making the flow error-prone.
Original source:
fe60b569ad/coderd/prebuilds/state.go (L13-L167)
#### Improvements After Refactoring:
- Simplified and broken down into smaller, focused helper methods.
- The flow of the function is now more linear and easier to understand.
- Struct initialization is cleaner, avoiding partial and incremental
mutations.
Refactored function:
eeb0407d78/coderd/prebuilds/state.go (L67-L84)
---
### 2) `ReconciliationActions` Struct
#### Issues Before Refactoring:
- The struct mixed both actionable decisions and diagnostic state, which
blurred its purpose.
- It was unclear which fields were necessary for reconciliation logic,
and which were purely for logging/observability.
#### Improvements After Refactoring:
- Split into two clear, purpose-specific structs:
- **`ReconciliationActions`** — defines the intended reconciliation
action.
- **`ReconciliationState`** — captures runtime state and metadata,
primarily for logging and diagnostics.
Original struct:
fe60b569ad/coderd/prebuilds/reconcile.go (L29-L41)
</details>
---------
Signed-off-by: Danny Kopping <dannykopping@gmail.com>
Co-authored-by: Sas Swart <sas.swart.cdk@gmail.com>
Co-authored-by: Danny Kopping <dannykopping@gmail.com>
Co-authored-by: Dean Sheather <dean@deansheather.com>
Co-authored-by: Spike Curtis <spike@coder.com>
Co-authored-by: Danny Kopping <danny@coder.com>
