Dynamically generate helm commands in CI

Fri, May 5, 2023 2-minute read

Dynamically generate helm commands in CI

We run helm for our deployments (eventually switching to Argo thankfully) and it works OK. What it doesn’t do well in is re-usability in CI.

We have a project which all other projects inherit from for CI and it works pretty well. It takes some organisation but once its done you can basically set and forget your deployments. Except that helm sucks for that and we ended up with each project needing a bespoke helm-deploy job.

This week I sat down and designed a better solution using python templating. Next week I think I’ll re-do it in Go because its in the standard lib.

Here’s how I’m doing it python.

import os
import re

from jinja2 import Template


def prefix(re_prefix: str):
  return re.compile(r"{prefix}\w".format(prefix=re_prefix))

helm_set = {key.replace(helm_set_prefix,"").replace("_","."):val for key, val in os.environ.items() if prefix(helm_set_prefix).match(key)}
helm_set_file = {key.replace(helm_set_file_prefix,"").replace("_","."):val for key, val in os.environ.items() if prefix(helm_set_file_prefix).match(key)}
# this is just an array
helm_values = [v for k,v in os.environ.items() if k.startswith(helm_values_prefix)]

template = """

helm upgrade --install {{ release }} {{ chart_path }} \
  {%- if helm_set -%}
    {%- for k,v in helm_set.items() -%}
  --set {{ k }}={{ v }} \
    {% endfor %}
  {% endif %}
  {%- if helm_set_file -%}
    {%- for k,v in helm_set_file.items() -%}
  --set-file {{ k }}={{ v }} \
    {% endfor %}
  {% endif %}
  {%- if helm_values -%}
    {%- for v in helm_values -%}
  --values {{ v }} \
    {% endfor %}
  {% endif %}
  --atomic --timeout {{ timeout }}

data = {
  "timeout": os.getenv("TIMEOUT", "300s"),
  "release": os.getenv("RELEASE"),
  "chart_path": os.getenv("CHART_PATH", "helm"),
  "helm_set": helm_set,
  "helm_set_file": helm_set_file,
  "helm_values": helm_values,

output = Template(template)

# run me like so:
# python main.py > script.sh

I’ll bypass the how of getting this going in CI jobs but to pass values its as simple as providing environment variables with prefixes.

    RELEASE: MyRelease
    HELM_SET_db_name: foobar
    HELM_SET_FILE_cacert: ca.crt
    HELM_VALUES: helm/values.yml

Which would create a bash script which looks like

helm upgrade --install MyRelease helm \
  --set db.name='foobar' \
  --set-file cacert='ca.crt' \
  --values 'helm/values.yml' \
  --atomic --timeout 300s

This script can then be executed in another job as needed when output as an artifact which makes its highly extensible.

Update: I also wrote this in Go which is nicer because you don’t need to install anything and can build it as a binary and pass around easier.


#python #ci #helm