helm update-values helper

tasks.py

# Details on usage see docstring
# 
# Installation:
#
# $ pip install invoke
# $ (copy/paste this file to your local tasks.py)
# 
# Usage:
# 
# 1. amend your values.yaml with a #==tags.myfeature (at line end of line to update)
# 2. $ invoke update-values -v values.yaml --specs "tags.myfeature=true"
# 3. use helm as usual
#
# Disclaimer: quick & dirty approach avoiding the hassle of yaml parsing
# 
# License: MIT
@task
def update_values(c, values_file=None, output_file=None, specs=None):
    """
    Update a helm values.yaml file by a --set compatible values string

    When setting tags in values.yaml where the tags are used as yaml anchors these are
    not updated when helm is called, see https://github.com/helm/helm/issues/5589
    
    This update-values task provides a solution.

    Args:
        c:
        values_file (str): filename of values file
        specs (str): commad separated key=values

    Usage:
        cloudmgr helm.update-values ./values.yaml --specs "tags.mytag=value"

        this will update the values.yaml file on the line that indicates, at 
        line end:
        
        #==tags.mytag 
        
        The corresponding line's value (the last string) is updated
        accordingly.

        Example:
        
            # values.yaml
            tags:
               ssl: true #==tags.ssl

        
        $ invoke update-values ./values.yaml --specs "tags.ssl=false"
        
        will replace ssl: true with ssl: false
        
            # values.yaml updated
            tags:
               ssl: fdalse #==tags.ssl
        
        Otherwise the values file is left untouched. This is idempotent, 
        that is the #== indicator is not removed.

        Only works with scalar/numeric and boolean values, strings not supported.

    Notes:
        * using jinja templating values.yaml does not help because jinja rendering is not
          indempotent. this would require to permanently keep a tempalte and
          a rendered version of values.yaml, which is confusing
        * using yaml anchors (as tags/flags/scalar values) is convenient since
          it allows to centralize global values in one place in values.yaml
        * using {{ tpl ... }} is sometimes a solution, but does not work when the values.yaml
          is driving imported helm charts that you don't want to or cannot change.

    Returns:
        saves updated values file
    """
    spec_vars = dict([pair.strip().split('=') for pair in specs.split(',')])
    with open(values_file) as fin:
        lines = fin.readlines()
    cur = None
    updated_lines = []
    for line in lines:
        if '#==' in line:
            orig, seek = line.split(' #==')
            tokens = orig.rstrip().split(' ')
            tokens[-1] = spec_vars[seek.replace('\n', '').strip()]
            new_line = ' '.join(tokens) + ' #==' + seek
            updated_lines.append(new_line)
        else:
            updated_lines.append(line)
    with open(output_file or values_file, 'w') as fout:
        fout.writelines(updated_lines)