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Plugin Development - File Structure

Note: This chapter assumes that you are familiar with Lua.

Consider your plugin as a set of Lua modules. Each file described in this chapter is to be considered as a separate module. Kong will detect and load your plugin's modules if their names follow this convention:

kong.plugins.<plugin_name>.<module_name>

Your modules of course need to be accessible through your package.path variable, which can be tweaked to your needs via the lua_package_path configuration property. However, the prefered way of installing plugins is through LuaRocks, which Kong natively integrates with. More on LuaRocks-installed plugins later in this guide.

To make Kong aware that it has to look for your plugin's modules, you'll have to add it to the plugins property in your configuration file, which is a comma-separated list. For example:

plugins = bundled,my-custom-plugin # your plugin name here

Or, if you don't want to load any of the bundled plugins:

plugins = my-custom-plugin # your plugin name here

Now, Kong will try to load several Lua modules from the following namespace:

kong.plugins.my-custom-plugin.<module_name>

Some of these modules are mandatory (e.g. handler.lua), and some are optional, and will allow the plugin to implement some extra-functionalities (e.g. api.lua to extend the Admin API endpoints).

Now let's describe exactly what are the modules you can implement and what their purpose is.


Basic plugin modules

In its purest form, a plugin consists of two mandatory modules:

simple-plugin
├── handler.lua
└── schema.lua
  • handler.lua: the core of your plugin. It is an interface to implement, in which each function will be run at the desired moment in the lifecycle of a request.
  • schema.lua: your plugin probably has to retain some configuration entered by the user. This module holds the schema of that configuration and defines rules on it, so that the user can only enter valid configuration values.

Advanced plugin modules

Some plugins might have to integrate deeper with Kong: have their own table in the database, expose endpoints in the Admin API, etc... Each of those can be done by adding a new module to your plugin. Here is what the structure of a plugin would look like if it was implementing all of the optional modules:

complete-plugin
├── api.lua
├── daos.lua
├── handler.lua
├── migrations
│   ├── cassandra.lua
│   └── postgres.lua
└── schema.lua

Here is the complete list of possible modules to implement and a brief description of what their purpose is. This guide will go in details to let you master each one of them.

Module name Required Description
api.lua No Defines a list of endpoints to be available in the Admin API to interact with entities custom entities handled by your plugin.
daos.lua No Defines a list of DAOs (Database Access Objects) that are abstractions of custom entities needed by your plugin and stored in the datastore.
handler.lua Yes An interface to implement. Each function is to be run by Kong at the desired moment in the lifecycle of a request.
migrations/*.lua No The corresponding migrations for a given datastore. Migrations are only necessary when your plugin has to store custom entities in the database and interact with them through one of the DAOs defined by daos.lua.
schema.lua Yes Holds the schema of your plugin's configuration, so that the user can only enter valid configuration values.

The Key-Auth plugin is an example of plugin with this file structure. See its source code for more details.


Next: Write custom logic ›

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