Installing custom dependencies in Kong Docker images

When using a custom plugin, there is sometimes a requirement to add some custom libraries for the plugin. How can the libraries be installed in a docker image for use in a Kubernetes deployment?

To create a custom image using the standard Kong image as a base, it is necessary to create a Dockerfile. The below example of a Dockerfile can be used to create a custom image that has an additional CLI tool and some lua packages installed;

FROM kong/kong-gateway:3.14.0.0

# Use the priviled root user to install new packages
USER root

# Install additional tools by using APT package manager here
# Example here is for adding the common tool jq into the image
# unzip is required by luarocks to install zip-packaged rocks
RUN apt-get update \
 && apt-get install -y jq unzip \
 && rm -rf /var/lib/apt/lists/*

# The lua package manger is installed by default with Kong 
# use the tool to install additional lua plugins

# Use the luarocks repository to install rock files
RUN ["luarocks", "install", "lua-resty-jwt"]

# Copy a local .rock file to the image and install it
COPY lua-zlib-1.2-0.linux-x86_64.rock /tmp
RUN luarocks install /tmp/lua-zlib-1.2-0.linux-x86_64.rock
RUN rm /tmp/lua-zlib-1.2-0.linux-x86_64.rock

# Switch back to the non-privileged kong user
USER kong

Note: the Enterprise -alpine image variant no longer exists; the default Kong Gateway image is now Ubuntu-based, so package installation uses apt-get rather than apk. Installing unzip is required before luarocks install, since zip-packaged rocks fail to install without it on the Ubuntu-based image.

To build the custom image, run the below command in the same directory and the Dockerfile;

docker build -t kong-with-jq-jwt .

This will create a local image with the tag kong-with-jq-jwt. You can use this in a docker-compose file like this;

image: kong-with-jq-jwt:latest

You can then push this image to your organizations docker repository with the docker push command.