Installing a Custom Plugin in Docker: Kong Plugin Development

By Venkata Reddy Bhavanam
Author LinkedIn:https://www.linkedin.com/in/venkatareddybhavanam/

This is the second post on installing a custom plugin in Kong API Gateway. Please check out the 1st post if you need a quick introduction to Kong and how to install a custom plugin in a VM.
In this post, we’ll learn how to install a custom plugin in Docker.

We’ll use the same custom plugin code as we used in the previous post.

Kong Plugin Development

Copying the code over here for completeness. The folder structure:

api-version/
├── handler.lua
└── schema.lua

The plugin name api-version and the contents of schema.lua

local typedefs = require "kong.db.schema.typedefs"

local PLUGIN_NAME = "api-version"

local schema = {
  name = "api-version",
  fields = {
    { consumer = typedefs.no_consumer },  -- this plugin cannot be configured on a consumer (typical for auth plugins)
    { protocols = typedefs.protocols_http },
    { config = {
        type = "record",
        fields = {
          { request_header = typedefs.header_name {
              required = true,
              default = "Hello-World" } },
          { response_header = typedefs.header_name {
              required = true,
              default = "Bye-World" } },
        },
        entity_checks = {
          { at_least_one_of = { "request_header", "response_header" }, },
          { distinct = { "request_header", "response_header"} },
        },
      },
    },
  },
}

return schema

Contents of handler.lua:

local typedefs = require "kong.db.schema.typedefs"

local PLUGIN_NAME = "api-version"

local schema = {
  name = "api-version",
  fields = {
    { consumer = typedefs.no_consumer },  -- this plugin cannot be configured on a consumer (typical for auth plugins)
    { protocols = typedefs.protocols_http },
    { config = {
        type = "record",
        fields = {
          { request_header = typedefs.header_name {
              required = true,
              default = "Hello-World" } },
          { response_header = typedefs.header_name {
              required = true,
              default = "Bye-World" } },
        },
        entity_checks = {
          { at_least_one_of = { "request_header", "response_header" }, },
          { distinct = { "request_header", "response_header"} },
        },
      },
    },
  },
}

return schema

Building the docker image:
We’ll take a base Kong image, add the plugin(and dependencies, if any), and use the final image. The Dockerfile

FROM kong/kong-gateway:3.2.2.1

**USER root**

# luarocks install dependency-name # to install any dependencies for cusotm plugin
RUN mkdir /usr/local/share/lua/5.1/kong/plugins/api-versionCOPY ./api-version /usr/local/share/lua/5.1/kong/plugins/api-version

Here, we are taking Kong base image kong/kong-gateway:3.2.2.1 and adding our plugin code.

We can now build it and run it with the following:

docker build -t kong-demo .
docker run -d --name kong-demo \
  -p "8000-8001:8000-8001" \
  -e "KONG_ADMIN_LISTEN=0.0.0.0:8001" \
  -e "KONG_PROXY_LISTEN=0.0.0.0:8000" \
  -e "KONG_DATABASE=off" \
  -e "KONG_LOG_LEVEL=debug" \
  -e "KONG_PLUGINS=bundled,api-version" \
  kong-demo

As you can see, we specify the custom plugin name along with the bundled plugins using KONG_PLUGINSenvironment variable.

Kong can be run either in DB mode using Postgres (and Cassandra, but it will be deprecated) or DB Less mode. We’ll use db-less mode and the following declarative config to create a service, route, and apply the plugin for this demo.

config.yaml
_format_version: "3.0"
_transform: trueservices:
  - name: demo
    url: https://mockbin.org
    plugins:
      - name: api-version
    routes:
      - name: demo-route
        paths:
          - /echo

Create the config with an API call to the admin API.

curl -X POST http://localhost:8001/config -F config=@config.yaml

Verify the custom plugin works by visiting the proxy URL. We’ll use HTTPie

http :8000/echo --headers
HTTP/1.1 200 OK
Bye-World: 0.1
...

That’s it. In the next post, we’ll see how to install the custom plugin in Kubernetes.

For more information: https://zelarsoft.com/