CouchDB Backup & Restore

Add support for CouchDB backup and restore functionality in Trove.

Launchpad Blueprint: https://blueprints.launchpad.net/trove/+spec/couchdb-backup-restore

Problem Description

CouchDB is one of the NoSQL databases that Trove supports. While Trove provides support for doing backups and restores, this functionality has not been implemented for CouchDB.

Proposed Change

The recommended method for doing full backups in CouchDB is to do a simple filesystem copy of the data files [1]. Since CouchDB does not officially support incremental backups, this feature will not be implemented in this release.

CouchDB is a document based database system where each database consist of several documents and each document is a JSON structure. In CouchDB, each document is associated with a revision number. Each database is stored as a single .couch file which is an append-only file (Every time a change is made to the document, it does not overwrite the existing document, instead it creates a new document with an updated version number). This makes it easy to do a full backup by simply copying this .couch file.

The following steps give a high level overview of the full backup and restore process for CouchDB.

Backup process is explained as follows:

  1. Locate the database files to be backed up. By default, the database files are located under /var/lib/couchdb directory (this location will be specified in the couchdb config file under /etc/couchdb directory). In CouchDB, each database is wholly contained in a single append-only file. This means that we can take a backup while its being written to.
  2. Compress and/or encrypt the database files and stream it to Swift storage.

Restore process is explained as follows:

  1. Stream and uncompress backup from storage to the database file directory (this location is specified in the /etc/couchdb config file)
  2. Change ownership of the files to the CouchDB user and group

Configuration

The following configuration options will be updated with the corresponding values for CouchDB:

  • backup namespace
  • restore namespace
  • backup_strategy

Database

None

Public API

None

Public API Security

None

Python API

None

CLI (python-troveclient)

The following commands will be functional for CouchDB after these changes:

  • backup-create
  • backup-delete
  • backup-list
  • create –backup

Internal API

None

Guest Agent

The CouchDB guestagent will be modified to add support for full backup and restore functionality. In addition, new strategies will also be added to support these new features.

The following guestagent file will be modified:
  • trove/guestagent/datastore/experimental/couchdb/manager.py
and the following new strategy files will be added for CouchDB:
  • trove/guestagent/strategies/backup/experimental/couchdb_impl.py
  • trove/guestagent/strategies/restore/experimental/couchdb_impl.py

Alternatives

Since CouchDB does not officially support incremental backups, an alternative to doing this is to use the CouchDB replication interface. CouchDB’s replication interface supports master-master replication model and replicates at the database level. It uses the REST API to trigger replication between databases on a source and target systems. If the databases are not on the same system, the source/target should be specified in a URI format:

http://<address>:<port>/<database name>

An example of a request for replicating database ‘db1’ from a local server to a remote server on x.x.x.x server would be:

curl -X POST -d ‘{“source”:”db1”,”target”:”http://x.x.x.x:5984:db1“}’
http://localhost:5984/_replicate

When replication is enabled for a database from a source to target system, it uses the document revision numbers to track differences and detect conflicts and resolve it.

Dashboard Impact (UX)

TBD (section added after approval)

Implementation

Assignee(s)

Mariam John (mariamj@us.ibm.com)

Milestones

Mitaka

Work Items

There will only be one work item for this feature. This includes implementing the strategies for CouchDB backup and restore and make the necessary guestagent changes. This will also include test-cases necessary to test the new functionalities.

Upgrade Implications

None

Dependencies

None

Testing

  • Add new test cases to test backup and restore functionality for CouchDB:

    • Add new unit tests to test the newly implemented functionality
    • Add a new CouchDB helper class to the existing integration-test framework.

Documentation Impact

The datastore documentation should be updated to reflect the enabled features.

Appendix

None