DuraCloud-Chronopolis Flow

Snapshot

1. In DuraCloud, content is added by the user into a Snapshot Storage Provider space. This is a staging area that is backed by S3.
2. The user selects a button in the space to create snapshot and enters snapshot metadata
3. The DuraCloud UI calls the storage provider snapshot task indicating space to snapshot
4. The snapshot task creates snapshot properties file and stores it in snapshot space
   1. When the snapshot properties file is added, the space is transitioned to read-only
5. The snapshot task calls to the bridge application to indicate that a snapshot needs to be taken, providing DuraCloud host/port/space
6. The bridge application adds an entry to the snapshot db table with the details of the snapshot action
7. The bridge application connects to DuraCloud and copies all content from DuraCloud space to bridge storage
   1. During transfer, content metadata is captured in a file
   2. During transfer, each content item is added to content db table (with snapshot id)
8. The bridge application creates a manifest for the content and verifies all content was transferred correctly
9. The bridge application sends a notification to chronopolis that a snapshot is ready
10. Chronopolis moves the content from bridge storage into preservation storage and constructs DPN bag 
    1.  Chronopolis validates against the manifest written by DuraCloud to the bridge storage
    2. Chronopolis creates the necessary bag files (bagit, bag-info, dpn-info) and registry entry for DPN
       
11. Chronopolis performs replication to other Chronopolis nodes and DPN
    
    1. Ace Tokens are created for other Chronopolis Nodes
    2. AMQP used to relay information about the state of replication
12. Chronopolis makes a call to the bridge application to indicate that content has been successfully copied to preservation storage
13. The bridge application deletes the directory in bridge storage used for the snapshot
14. The bridge application makes a call to a task in the DuraCloud Chronopolis provider to indicate that it is now time to clean up the snapshot content
15. The cleanup task sets a policy on the underlying S3 bucket which causes the content to be removed within 24 hours
16. The bridge application watches the snapshot space, and when it becomes empty, calls the snapshot complete task, which clears the S3 bucket policy
17. The bridge application notifies the user who requested the snapshot that it has been completed

Snapshot Display

1. A DuraCloud user selects the Snapshot Storage Provider in the DuraCloud UI
2. The DuraCloud UI (DurAdmin) make the usual call to get spaces and also calls a task in the Snapshot Storage Provider to request a list of snapshots
3. The snapshots task calls the bridge application to request a list of snapshots
   1. Note: DuraCloud is not aware of the snapshot database. All communication with the db goes through the bridge application.
4. The bridge application queries the database (snapshot table) to retrieve a listing of snapshots which are visible to the given DuraCloud account
5. The bridge application returns list of snapshots, which are passed back up the chain to the UI
6. The DuraCloud UI displays the list of snapshots alongside the traditional spaces in a way the distinguishes the two sets, providing a Restore button on each snapshot space
7. When a snapshot space is selected, a call to another task in the Snapshot Storage Provider is made to retrieve the listing of content items
8. The snapshot content item task calls the bridge application to request the list of content in a snapshot
9. The bridge application queries the database to retrieve the listing of content
10. The bridge application returns the first X items, which is passed back up the chain to the UI
11. The DuraCloud UI displays the list of content items in the same way it would display content items for a traditional space
12. Requests for more items in the content listing follow the same pattern, but with a parameter to indicate offset

Restore

1. The DuraCloud user browses the snapshot listings and clicks the "Restore" button on a snapshot
2. The DuraCloud UI calls a DuraCloud Restore task
3. The DuraCloud Restore task creates a space where the restored content will be placed and calls the bridge application with a restore request
   1. A bucket policy will be added to the space to delete content after a set time period (3 weeks? a month?)
4. The bridge application adds an entry to the restore db table
5. The bridge application creates a directory in bridge storage and sends a notification to Chronopolis to request a restore action
6. Chronopolis copies the contents of the snapshot DPN bag to the bridge storage directory
   1. Chronopolis will validate the files on the bridge storage against the manifest in the bag (originally created during the snapshot phase) 
   2. BagIt files are omitted during the copy, leaving only the files which were originally written by the bridge application
      
7. The bridge application copies content from bridge storage to DuraCloud space
8. The bridge application reads the content metadata file and updates each content item with its metadata values
9. The bridge application verifies (based on manifest) that content transferred to DuraCloud is consistent with the content that was originally in DuraCloud (pre-snapshot)
10. The bridge application deletes the directory in bridge storage used for the restore action
11. The bridge application notifies the user who requested the restoration that the process is complete, informs them of the space ID where they can find their content, and tells them the date on which the content will be removed