Bash

warning

We recommend reviewing Docker's best practices before attempting to create a custom plugin.

We recommend that all plugins be placed inside a scratch image.

Overview

From Bash documentation:

Bash is the GNU Project's shell. Bash is the Bourne Again SHell. Bash is an sh-compatible shell that incorporates useful features from the Korn shell (ksh) and C shell (csh).

It is intended to conform to the IEEE POSIX P1003.2/ISO 9945.2 Shell and Tools standard. It offers functional improvements over sh for both programming and interactive use. In addition, most sh scripts can be run by Bash without modification.

Code

To create a plugin using Bash, we'll need to first decide what task we want this plugin to accomplish.

For this example, we're going to create a script that runs a curl command from the provided input:

#!/usr/bin/env bash

# import method parameter from environment
method=${PARAMETER_METHOD}
# import body parameter from environment
body=${PARAMETER_BODY}
# import url parameter from environment
url=${PARAMETER_URL}

# send curl request from provided input
curl \
  -X "${method}" \
  -d "${body}" \
  "${url}"

tip

An example of this code is provided in the bash section of the go-vela/vela-tutorials repository.

Image

Once we have the executable needed to accomplish our plugin's task, we need to create a Dockerfile to produce an image.

This image should contain the script and be setup to run that script when the plugin is executed:

FROM alpine

RUN apk add --update --no-cache bash ca-certificates curl

COPY vela-sample.sh /bin/vela-sample.sh

ENTRYPOINT ["bash", "/bin/vela-sample.sh"]

tip

An example of this image is provided in the target/vela-sample Docker repository.

Publishing

In order to run the plugin in a pipeline, we'll need to make sure we build and publish it to a Docker registry:

# build the image
docker build -t target/vela-sample:bash .

# publish the image
docker push target/vela-sample:bash

info

This has the added benefit of enabling others in the community to consume your plugin!

Troubleshooting

To verify that the plugin performs the desired task, it can be executed locally via the command line:

docker run --rm \
  -e PARAMETER_BODY="This is a sample Vela plugin written with Bash" \
  -e PARAMETER_METHOD="POST" \
  -e PARAMETER_URL="http://vela.localhost.com" \
  target/vela-sample:bash

Usage

After publishing the image to a Docker registry, it can be referenced in a pipeline:

version: "1"

steps:
  - name: sample bash plugin
    image: target/vela-sample:bash
    pull: always
    parameters:
      url: http://vela.localhost.com
      method: POST
      body: |
        This is a sample Vela plugin written with Bash