Alchemy

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Replace ​

It is some times impossible to UPDATE a resource, e.g. you cannot rename a R2 Bucket name. In these cases, you need to perform a REPLACE operation to:

  1. create a new version of the Resource and update references
  2. delete the old version of the Resource (or leave it orphaned)

Trigger Replacement ​

During the update phase, you can trigger a replacement by calling this.replace():

typescript
// Implementation pattern
if (this.phase === "update") {
  if (this.output.name !== props.name) {
    // trigger replace and terminate this `"update"` phase
    this.replace();
    // (unreachable code)
  } else {
    return updateResource();
  }
}

Create new ​

After you call this.replace(), the "update" phase will terminate and be re-invoked with "create" (to create the new resource).

ts
if (this.phase === "create") {
  return createNewResource();
}

Delete old ​

After all downstream dependencies have been updated and you finally call app.finalize(), Alchemy will then invoke the "delete" phase on the old resource.

ts
const app = await alchemy("app");

// ... create resources

await app.finalize(); // finalize scopes by deleting "orphaned" and "replaced" resources