5.3. Backing up CouchDB

CouchDB has three different types of files it can create during runtime:

  • Database files (including secondary indexes)
  • Configuration files (*.ini)
  • Log files (if configured to log to disk)

Below are strategies for ensuring consistent backups of all of these files.

5.3.1. Database Backups

The simplest and easiest approach for CouchDB backup is to use CouchDB replication to another CouchDB installation. You can choose between normal (one-shot) or continuous replications depending on your need.

However, you can also copy the actual .couch files from the CouchDB data directory (by default, data/) at any time, without problem. CouchDB’s append-only storage format for both databases and secondary indexes ensures that this will work without issue.

To ensure reliability of backups, it is recommended that you back up secondary indexes (stored under data/.shards) prior to backing up the main database files (stored under data/shards as well as the system-level databases at the parent data/ directory). This is because CouchDB will automatically handle views/secondary indexes that are slightly out of date by updating them on the next read access, but views or secondary indexes that are newer than their associated databases will trigger a full rebuild of the index. This can be a very costly and time-consuming operation, and can impact your ability to recover quickly in a disaster situation.

On supported operating systems/storage environments, you can also make use of storage snapshots. These have the advantage of being near-instantaneous when working with block storage systems such as ZFS or LVM or Amazon EBS. When using snapshots at the block-storage level, be sure to quiesce the file system with an OS-level utility such as Linux’s fsfreeze if necessary. If unsure, consult your operating system’s or cloud provider’s documentation for more detail.

5.3.2. Configuration Backups

CouchDB’s configuration system stores data in .ini files under the configuration directory (by default, etc/). If changes are made to the configuration at runtime, the very last file in the configuration chain will be updated with the changes.

Simple back up the entire etc/ directory to ensure a consistent configuration after restoring from backup.

If no changes to the configuration are made at runtime through the HTTP API, and all configuration files are managed by a configuration management system (such as Ansible or Chef), there is no need to backup the configuration directory.

5.3.3. Log Backups

If configured to log to a file, you may want to back up the log files written by CouchDB. Any backup solution for these files works.

Under UNIX-like systems, if using log rotation software, a copy-then-truncate approach is necessary. This will truncate the original log file to zero size in place after creating a copy. CouchDB does not recognize any signal to be told to close its log file and create a new one. Because of this, and because of differences in how file handles function, there is no straightforward log rotation solution under Microsoft Windows other than periodic restarts of the CouchDB process.