priority-updater

Tool to quickly create a plugin with an updated priority.

Status

early development

Description

Kong plugin priorities are static, in source. Occasionally there is a use-case for a different priority setting, in which case the user is advised to create a copy of the original plugin and modify the source.

This utility makes this process a lot easier. It creates a wrapper plugin that takes the original plugin and adjusts the priority.

There are two main uses:

1. Executing plugins in a different order
2. Running the same plugin functionality twice or more (create indentical plugins with slightly different priorities)

WARNING!

Do NOT upload the generated plugins to LuaRocks since that would pollute the LuaRocks repository with loads of useless/duplicate plugins.

Usage

1. Create a wrapper for the 'request-transformer' with priority '999':

   ./create.sh "request-transformer" 999

   New rock is generated: kong-plugin-request-transformer_999-0.1-1.all.rock. The new plugin name is request-transformer_999 (the old name with the appended new priority)

2. Copy the resulting .rock file to the target system. Or use the docker tools to inject it into a Kong docker image.

3. Install the plugin on your Kong system using LuaRocks

   luarocks install kong-plugin-request-transformer_999-0.1-1.all.rock

4. Use your new plugin with Kong (use the NEW name with priority!)

   curl -X POST http://kong:8001/plugins \
       --data "name=request-transformer_999"  \
       --data "config.remove.headers=x-toremove, x-another-one"

Requirements/Prerequisites

The utility is a bash script that uses a docker build container. Hence only those are required to run it.

Implementation details

• The plugin does not contain any functional code, but shares everything with the original:
  • if the original code gets updated, the wrapper will use the updated code.
  • the new plugin shares the same management API endpoints and data (DAO's).
• There is no performance penalty for using the wrapper.
• One caveat: If a plugin uses its own table to store state (eg. updates values in self), then that is the only part that is NOT shared. Afaik there are currently no such plugins.

History/Changelog

Note: the version is the version of the generated wrapper code, and independent of the original code. If the Lua code of the wrapper changes, then also change the version at:

• the generated wrapper in priority.lua, the WRAPPER_VERSION constant
• the VERSION in handler.lua

0.4 14-Apr-2020

• Fix: workaround for a LuaJIT bug.

0.3 14-Dec-2020

• Fix: fix in version 0.2 was incomplete, the new error could be the existing plugins name, instead of the new name.

0.2 04-Dec-2020

• Fix: plugins with daos.lua or api.lua would fail on more recent versions of Kong because it checks the exact error message.

0.1 12-Jun-2019

• Initial version