Pulumi Engine and Provider Schema Versioning: Rollback Compatibility After Breaking Changes?

Answer

No, Pulumi does not automatically guarantee rollback compatibility when a provider schema undergoes breaking changes; the engine will refuse to plan a rollback if the current provider version cannot validate the historically stored state.

Confirmed facts

• The provider plugin version and schema version used for each resource are recorded in the stack state file.
• During an update or preview the engine loads that exact provider version to validate and diff resources.
• If the provider is upgraded with a breaking schema change (e.g., a required input removed or a computed output deleted) and the original version is no longer available, the engine returns a schema‑mismatch error and aborts the rollback preview.
• Rollback succeeds only when the provider version originally used to create the resources remains installed and compatible.
• Users can preserve rollback safety by pinning the provider version in Pulumi.yaml or by exporting the state, manually migrating it to the new schema, and reimporting.

Likely explanation

The Pulumi engine treats the recorded provider version as a contract for state validation. It does not include an automatic translation layer that rewrites historical state to match a newer schema, because such a migration could drift from the actual cloud resources without user verification. Consequently, when the contract cannot be satisfied by the current provider, the engine stops the planning step to prevent potentially unsafe operations.

Steps to restore rollback safety

1. Export the stack state: pulumi stack export > state.json.
2. Locate the version field under each resource’s provider to identify the original provider version.
3. Ensure that exact version is installed: pulumi plugin install provider or pin it in Pulumi.yaml.
4. If the original version is unavailable, export the state, manually adjust the recorded provider version and any schema‑incompatible fields, then reimport: pulumi stack import --file state.json.
5. After aligning the provider, run pulumi up --target-retain or a preview to verify that rollback planning succeeds.

Missing diagnostic detail

Do you have access to the original provider version that was used to create the resources? Knowing whether that version can be installed changes the recommendation from pinning/reinstalling the old version to performing a manual state migration.