Closes https://github.com/coder/internal/issues/369
We can't know whether a replacement (i.e. drift of terraform state
leading to a resource needing to be deleted/recreated) will take place
apriori; we can only detect it at `plan` time, because the provider
decides whether a resource must be replaced and it cannot be inferred
through static analysis of the template.
**This is likely to be the most common gotcha with using prebuilds,
since it requires a slight template modification to use prebuilds
effectively**, so let's head this off before it's an issue for
customers.
Drift details will now be logged in the workspace build logs:
Plus a notification will be sent to template admins when this situation
arises:
A new metric - `coderd_prebuilt_workspaces_resource_replacements_total`
- will also increment each time a workspace encounters replacements.
We only track _that_ a resource replacement occurred, not how many. Just
one is enough to ruin a prebuild, but we can't know apriori which
replacement would cause this.
For example, say we have 2 replacements: a `docker_container` and a
`null_resource`; we don't know which one might
cause an issue (or indeed if either would), so we just track the
replacement.
---------
Signed-off-by: Danny Kopping <dannykopping@gmail.com>
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>
