# Migrate Backblaze B2 S3 bucket: Generated downloads

Move object storage from Backblaze B2 S3 bucket to Ample, one component at a time.

**Destination verified on Ample**: an export query rendered to a CSV artifact stored with metadata in a private bucket and returned only to an authorized caller (401 without token, export=ok rows=3).

**Source procedure**: Inventory the bucket with `rclone size` or the B2 dashboard.

**Not migrated automatically**: B2 file versions, lifecycle rules and application-key restrictions are not migrated.

## Cutover
Switch the app's S3_* environment to the Ample bucket with a redeploy, verify reads and writes, keep B2 read-only until confirmed.

## Rollback
Keep the source untouched until you confirm; nothing at the source is changed or deleted by this guide.

### Prerequisites
- Authorized access to the Backblaze B2 S3 bucket source and its export tooling
- An inventory of every component in scope and out of scope
- A validated backup or copy before any cutover
- An Ample account token with servers:write, buckets:write

## Workflow Steps
1. **Inventory the source**  
List what Backblaze B2 S3 bucket provides beyond the component you are moving. Out of scope here: B2 file versions, lifecycle rules and application-key restrictions are not migrated.

2. **Source step 1**  
Inventory the bucket with `rclone size` or the B2 dashboard

3. **Source step 2**  
Copy objects with `rclone sync` from the B2 S3-compatible endpoint to the Ample bucket endpoint using the issued credentials (path-style)

4. **Source step 3**  
Verify a sample of objects by size and checksum after the copy

5. **Create the destination bucket and copy**  
Create the bucket, copy with rclone or the S3 CLI in path-style mode using the issued credentials, then pass the credentials to the app as encrypted S3_* variables.

6. **Validate before cutover**  
Run the app's own checks and, for data, compare counts and checksums; the example checks are the pattern self-tests (/p/generated-downloads).

7. **Cut over**  
Switch the app's S3_* environment to the Ample bucket with a redeploy, verify reads and writes, keep B2 read-only until confirmed.

8. **Rollback**  
Point DNS or configuration back to the source. The source was never modified; deletion is a separate, user-executed step after validation.

### Success Checks
- **Destination app responds on its public URL**  
  - **Kind**: http_get  
  - **Path**: /  
  - **Expect**: ample canary express patterns

- **Generated-downloads check from the destination example**  
  - **Kind**: http_get  
  - **Path**: /p/generated-downloads  
  - **Expect**: see the pattern fixture checks

- **Data or object counts and checksums match the source**  
  - **Kind**: manual  
  - **Expect**: operator comparison before cutover

### Limitations
- Documentation only: nothing is executed automatically and no execution binding is offered.
- The source-side procedure is documented from Backblaze B2 S3 bucket's standard tooling and was not executed in this catalog's evidence; the destination side was verified with the pattern fixture.
- No full source-product parity is claimed: B2 file versions, lifecycle rules and application-key restrictions are not migrated.
- Verified on the node-22 template at s-1vcpu-1gb; region, compliance and request-duration limits are unknown.
- PutObject and GetObject with path-style addressing are verified; bulk copy tooling and other S3 operations are not.