Hot-Patch EMQX at Runtime

Starting from 4.3, EMQX supports an easier (comparing to 4.2) hot-patch mechanism. Hot-patch is an ad-hoc patch mechanism comparing to Hot Upgrade. For certain urgent issues, a hot-patch can be applied before the fix is included in a (future) official release.

NOTE

It's recommended to upgrade to the offical release which included the patched fixes. The patched modules should be deleted before upgrading.

Steps to Patch

1. Get the list of modules to be updated from EMQX support team. For example:

emqx.beam
emqx_rule_engine.beam

2. Copy the files to data/patches directory

cp /path/to/patch/emqx.beam data/patches
cp /path/to/patch/emqx_rule_engine.beam data/patches

The exact path to the data/patches directory depends on configuration and installation. Typically, it is:

• 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

3. Load new files at runtime:

$ emqx eval 'c:lm().'
[{module, emqx},
{module, emqx_rule_engine}]

Rollback the Patched Modules

In case the patch does not work as expected, or if one wish to go back to the state before patching, below are the steps to rollback.

1. Delete the patched modules from the data/patches directory

$ mv data/patches/emqx.beam /tmp/
$ mv data/patches/emqx_rule_engine.beam /tmp/

2. reload the beam files:

$ emqx eval 'c:lm().'
[{module, emqx},
{module, emqx_rule_engine}]