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Write plugins in Python

The Python PDK

Kong Gateway support for Python plugin development is provided by the kong-python-pdk library. The library provides a plugin server and Kong-specific functions to interface with Kong Gateway.

Install

To install the plugin server and PDK globally, use pip:

pip3 install kong-pdk

Development

A Kong Gateway Python plugin implementation has following attributes:

Schema = (
    { "message": { "type": "string" } },
)
version = '0.1.0'
priority = 0
class Plugin(object):
  pass

A class named Plugin defines the class that implements this plugin.
A dictionary called Schema that defines expected values and data types of the plugin.
The variables version and priority that define the version number and priority of execution respectively.

Note: This repository contains example Python plugins and an API reference.

Phase handlers

You can implement custom logic to be executed at various points of the request processing lifecycle. To execute custom code during the access phase, define a function named access:

class Plugin(object):
    def __init__(self, config):
        self.config = config
    def access(self, kong):
      pass

You can implement custom logic during the following phases using the same function signature:

certificate
rewrite
access
response
preread
log

The presence of the response handler automatically enables the buffered proxy mode.

Notes: A positional argument is required in the definition of the phase handler method. In the example below, the positional argument is called kong. The positional argument can be used as the PDK function’s root object, which means that you can call specific PDK functions by using this argument, like kong.log.info or kong.request.get_header.

Type hints

Support for type hints is available. To use type hints and autocomplete in an IDE, add the kong parameter to the phase handler function:

import kong_pdk.pdk.kong as kong
class Plugin(object):
    def __init__(self, config):
        self.config = config
    def access(self, kong: kong.kong):
        host, err = kong.request.get_header("host")

Warning: Classes and functions in the kong_pdk.pdk.kong module cannot be used directly because they’re only used for type hints. To call PDK functions, use the kong object that is passed as the phase handler’s parameter. Keep in mind that if you want to call PDK functions outside of the phase handler, you also need to pass the kong object to your outer code.

Here is an example of using the PDK functions outside of the Plugin class:

import kong_pdk.pdk.kong as kong

def example_access_phase(kong: kong.kong):
    host_header, err = kong.request.get_header("host")
    kong.log.info(host_header)

class Plugin(object):
    def __init__(self, config):
        self.config = config
    def access(self, kong: kong.kong):
        example_access_phase(kong)

Embedded server

To use the embedded server, use the following code:

if __name__ == "__main__":
    from kong_pdk.cli import start_dedicated_server
    start_dedicated_server("py-hello", Plugin, version, priority)

The first argument to start_dedicated_server defines the plugin name and must be unique.

Example configuration

To load plugins using the kong.conf configuration file, you have to map existing Kong Gateway properties to aspects of your plugin. Below are two examples of loading plugins within kong.conf.

pluginserver_names = my-plugin,other-one
pluginserver_my_plugin_socket = /usr/local/kong/my-plugin.socket
pluginserver_my_plugin_start_cmd = /path/to/my-plugin.py
pluginserver_my_plugin_query_cmd = /path/to/my-plugin.py --dump
pluginserver_other_one_socket = /usr/local/kong/other-one.socket
pluginserver_other_one_start_cmd = /path/to/other-one.py
pluginserver_other_one_query_cmd = /path/to/other-one.py -dump

The socket and start command settings coincide with their defaults and can be omitted:

pluginserver_names = my-plugin,other-one
pluginserver_my_plugin_query_cmd = /path/to/my-plugin --dump
pluginserver_other_one_query_cmd = /path/to/other-one --dump

If you want to open verbose logging, pass the -v argument to the start command line:

pluginserver_my_plugin_start_cmd = /path/to/my-plugin.py -v

Concurrency model

The Python plugin server and the embedded server support concurrency. By default, the server starts in multi-threading mode.

If your workload is IO intensive, you can use the Gevent model by passing the -g flag to start_cmd in kong.conf. If your workload is CPU intensive, consider the multi-processing model by passing the -m flag to start_cmd in kong.conf.