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Python

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 Python documentation:

Python is a programming language that lets you work quickly and integrate systems more effectively.

Code​

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

For this example, we're going to create a program that makes an HTTP request from the provided input:

#!/usr/bin/env python

import http.client
import os
import urlparse

# import method parameter from environment
method = os.getenv['PARAMETER_METHOD']
# import body parameter from environment
body = os.getenv['PARAMETER_BODY']
# import url parameter from environment
url = os.getenv['PARAMETER_URL']

# capture full URI from url
uri = urlparse(url)

# create new HTTP connection from URL
conn = http.client.HTTPSConnection(uri.hostname, uri.port)

# create headers to be added to request
headers = {}

# send HTTP request
conn.request(method, uri.path, body, headers)

# capture the response
response = conn.getresponse()

# output the response
print(response.read().decode("utf-8"))
info

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

Image​

Once we have the script 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 python:alpine

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

COPY vela-sample.py /bin/vela-sample.py

ENTRYPOINT ["python", "/bin/vela-sample.py"]
info

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:python .

# publish the image
docker push target/vela-sample:python
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 Python" \
  -e PARAMETER_METHOD="POST" \
  -e PARAMETER_URL="http://vela.localhost.com" \
  target/vela-sample:python

Usage​

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

version: "1"

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