Custom plugins not loading with no LuaRocks module found for `kong.plugins.base_plugin`

When starting a Kong EE 3.x instance, custom plugins are causing the startup to fail. There is an error shown for a missing LuaRocks module kong.plugins.base_plugin. For example;

2026/08/27 07:18:53 [error] 1#0: init_by_lua error: /usr/local/share/lua/5.1/kong/tools/module.lua:36: error loading module 'kong.plugins.my-custom-plugin.handler':
/usr/local/share/lua/5.1/kong/plugins/my-custom-plugin/handler.lua:1: module 'kong.plugins.base_plugin' not found:No LuaRocks module found for kong.plugins.base_plugin
no field package.preload['kong.plugins.base_plugin']

The significant message is:

module 'kong.plugins.base_plugin' not found:No LuaRocks module found for kong.plugins.base_plugin
no field package.preload['kong.plugins.base_plugin']

The code for the custom plugin is inheriting from the base_plugin module. This module has been deprecated from 2.4.1.0 and has been removed in 3.0.0.0.

The BasePlugin class was deprecated in Kong v2.4.x and will be removed in v3.0.x. Plugins that extend base_plugin.lua will continue to work until v3.0.x but should be updated to the newer, simpler pattern.

You will need to update your plugin to use the newer code format as per the docs.