Creating custom plugins with Bash

by bradrydzewski

This provides a brief tutorial for creating a Drone webhook plugin, using simple shell scripting, to make an http requests during the build pipeline. The below example demonstrates how we might configure a webhook plugin in the Yaml file:

pipeline:
  webhook:
    image: foo/webhook
    url: http://foo.com
    method: post
    body: |
      hello world

Create a simple shell script that invokes curl using the Yaml configuration parameters, which are passed to the script as environment variables in uppercase and prefixed with PLUGIN_.

#!/bin/sh

curl \
  -X ${PLUGIN_METHOD} \
  -d ${PLUGIN_BODY} \
  ${PLUGIN_URL}

Create a Dockerfile that adds your shell script to the image, and configures the image to execute your shell script as the main entrypoint.

FROM alpine
ADD script.sh /bin/
RUN chmod +x /bin/script.sh
RUN apk -Uuv add curl ca-certificates
ENTRYPOINT /bin/script.sh

Build and publish your plugin to the Docker registry. Once published your plugin can be shared with the broader Drone community.

docker build -t foo/webhook .
docker push foo/webhook

Execute your plugin locally from the command line to verify it is working:

docker run --rm \
  -e PLUGIN_METHOD=post \
  -e PLUGIN_URL=http://foo.com \
  -e PLUGIN_BODY="hello world" \
  foo/webhook