Kong plugin tag-executor

This plugin is designed specifically for Kong dbless with declarative config mode of operation. If you're running Kong with database and have outside tools/pipelines that control Kong's configuration this plugin is of little use to you.

Goal of this plugin is to reduce duplication of huge plugin configurations for cases when plugins must be configured on specific routes (especially when number of services and routes increases in your project all the time).

For this particular reason plugin utilizes Route tags to determine if plugin phases should be invoked. (It feels like this feature belongs inside Kong's core functionality like it's done today with route, service, consumer references, but for now this plugin will do the job).

Installation

Install the plugin using luarocks

luarocks install kong-plugin-tag-executor

Capabilities

Plugin can use configuration of any other plugin installed in Kong instance referenec docs.
Plugin is designed to work with declarative_config only (Tested only against dbless Kong). In theory can work in 'Kong with DB' environments.
Execution of nested plugins and their phases respects Kong's plugin execution order.
Plugin is executed before any other plugin (has pretty High Priority)
Plugin is supposed to be global (targeting tags provides really fine grained control).
Can be used on specific routes, services, consumers (which defeats the purpose).

Limitations

Providing nested plugin configuration for tag-executor itself (self-config) has no effect. tag-executor plugin is omitted from phase executions to avoid potential overflows due to recursive calls.
Works only with HTTP/HTTPS requests (No stream support yet?).

Example

Below is the example configuration one might use in declarative_config:

- name: tag-executor
  config:
    tag_execute_steps:
      - name: service-tracing-step
        target_tag: tracing
        plugins:
          - name: correlation-id
            config:
              header_name: correlation-id
              generator: uuid
              echo_downstream: true
          - name: request-transformer
            config:
              add:
                headers:
                  - X-Traced-With:correlation
      - name: another-step
          # More and more configurations

Whenever Kong receives a request this plugin invokes each of tag_execute_steps. In this example when route that has tracing tag is matched, correlation-id and request-transformer plugins are invoked and request to upstream gets modified by the plugins.

Configuration

Property	Description
`name` required Type: string	The name of the plugin, in this case `tag-executor`.
`config.tag_execute_steps` required Type: array of record elements	The steps to invoke on each phase of the plugin.
`config.tag_execute_steps.[?].name` required Type: string	Unique name of this step.
`config.tag_execute_steps.[?].target_tag` optional Type: string	Tag to match on `route`. If not specified applies steps to all routes.
`config.tag_execute_steps.[?].plugins` required Type: array of plugin configurations	Configurations of plugins to execute (Kong declarative configuration format). Refer to particular plugin documentation for configuration reference.

Notes to self/TODO

Upload to Luarocks via GH Actions
Write docs for Kong plugin hub
More testing