Config and data backup & restore

EMQX is highly available when clustered, and most of the data in EMQX cluster is fully replicated to all nodes — However, we should still plan for the worst. Let’s discuss data backup and restore for disaster recovery.

Terminologies

Mnesia (opens new window): The name of the built-in database inside each EMQX node. Data export import: A command line tool to support data export & import using a JSON file as the transient drop.

Files

Config files

When using morden provisioning tools for EMQX deployment, configuration changes are mostly managed by the tools, and even source controlled in for example a git repo.

In case manual config changes are made to the config files, it’s a good idea to have them backed up.

The config files are possibly located in below places, but it differ depending on installation

• Default to /etc/emqx when installed from RPM or DEB packages
• Default to /opt/emqx/etc shen running in docker container
• In /path/to/install/dir/etc when directly extracted from zip package.

Mnesia Database

There are two approaches to create a backup of the Mnesia database.

Export ‘mnesia’ data

The commands introduced in Data import and export, can be used backup the database to a JSON file using the export command, and restore whth the import command.

When recovering a EMQX cluster from the exported file, the new EMQX cluster should be started with at empty state, and the import command should repopulate the database for all nodes in the cluster.

Backup ‘mnesia’ dir

In EMQX Mnesia database, tables are stored in the mnesia sub directory in EMQX’s data directory. Backing up the database can be as simple as making a copy of all the files in the mnesia directory.

The database schema (which is also stored in mnesia directory) is unique per EMQX node, meaning a backup can not be used to restore another node in the cluster.

Depending on installation and configuration, data dir can be located in below possible paths.

• Where the environment variable EMQX_NODE__DATA_DIR points to
• Where the node.data_dir config key points to in emqx.conf
• /opt/emqx/data when running in docker (typically a mounted volume)
• <install-path>/data when installed from zip package extraction
• /var/lib/emqx/ when installed from RPM or DEB packages

What about Persisted Sessions ?

Prior to v5.0, EMQX nodes are rather stateless by themselves, in the sense that persistent session states are delegated to external databases (EMQX Enterprise feature).

So, for persisted sessions, there is nothing to backup from where the EMQX nodes are running.