kreate-kube 0.3.0

kreate kubernetes application from templates

kreate-kube

kreate kubernetes/kustomize yaml files based on templates

The purpose of the kreate-kube framework is to easily create kubernetes resources for an application. This is especially useful if you have many different applications that you would like to keep as similar as possible, while also having flexibility to tweak each application.

Installing and running kreate-kube

Installing

The kreate-kube framework is available on PyPi. To install it, you will need:

• python3 At least version 3.8 is needed.
• venv virtual environments in Python when you need to use different versions of the framework.
• pip package installer for python, to install packages

To create a virtual environment with kreate-kube in a Linux or Unix environment (like MacOs) one should:

python3 -m venv .venv         # create a virtual environment in the .venv directory
. .venv/bin/activate          # activate the virtual environment
python3 -m pip  kreate-kube   # install the latest version of kreate-kube

This will install the kreate-kube package, including a script kreate that can be called from the commandline.

Note: For Windows the commands might be slightly different, but venv and pip are well documented in the Python community.

Running

You can now call the kreate command line. Some examples:

kreate -h          # show help info
kreate version     # show the version

kreate files   # kreate all files based on the konfig.yaml in the current directory
kreate         # The same (files is the default command)

kreate diff    # kreate output that shows differences between the kreate and a real kubernetes cluster
kreate apply   # apply the kreated files to a kubernetes cluster

Note: for diff and apply your .kube/config should be set up correctly

By default kreate It will look for a file konfig.yaml in your current directory. It is possible to specify a different directory or file using the --konfig option. If this is a directory it will look for a konfig.yaml file in this directory.

Example using application structure file

Kreating resources is based on a application strukture definition file. Usually there are ate least 3 files needed for a setup:

• konfig.yaml ties all together
• <app>-strukture.yaml describes the structure of all application components
• values-<app>-<env>.yaml contains specific values for a certain environment Note that these filename may be changed.

demo-strukture.yaml

The structure file is a yaml describing in a high level which resources are needed:

Deployment:
  main:
    vars:
    - demo-vars
    secret-vars:
    - demo-secrets
    patches:
      AntiAffinityPatch: {}
      HttpProbesPatch: {}
      AddEgressLabelsPatch: {}

Egress:
  db:
    name: egress-to-db
    cidr_list: {{ val.db_egress_cidr_list }}
    port: {{ val.db_port }}

Ingress:
  all:
    host: {{ val.ingress_host_internal }}
    path: /
    options:
      - basic_auth

Kustomization:
  main:
    configmaps:
      demo-vars:
        vars:
          ENV: {{ val.env }}
          DB_URL: {{ val.DB_URL }}

Secret:
  main:
    name: demo-secrets
    vars:
      DB_PSW: {{ secret.DB_PSW | dekrypt() }}
      DB_USR: {{ secret.DB_USR }}

SecretBasicAuth:
  basic-auth:
    users:
      - admin
      - guest

Service:
  main:
    name: demo-service

Note: This shows only a small subset of possibilities of kreate-kube

konfig.yaml

The konfig.yaml ties everything together:

• Some general values (mainly application name and enviroment)
• extra environment specific "stuff" to load
  • values such as IP numbers and urls
  • secrets such as usernames and passwords
• what strukture file(s) to use In general values and secrets will be loaded from separate files, to keep the konfig.yaml file simple, and to separate this environment specific part separated.

The file can contain several other things as well:

• files to be mounted in a pod, such as application configuration files
• secret_files as files, but encrypted and stored as kubernetes Secret
• extra custom templates for resources and patches

Below is a simple but typical example.

{% set appname = "demo" %} # reuse the appname in rest of this file
{% set env = "acc" %}      # reuse the env in rest of this file
values:
  vars:
    appname: {{ appname }}
    env: {{ env }}
    team: knights
    project: kreate-kube-demo
    image_version: 2.0.2
  files:
    - values-{{appname}}-{{env}}.yaml
secrets:
  files:
    - secrets-{{appname}}-{{env}}.yaml

strukture_files:
  - {{appname}}-strukture.yaml

Note: In a future version, the value-files, secrets-files and strukture_files might use sane defaults (as allready shown using {{ appname }} and {{ env }}), so these section might be omitted in the future

Versions of kreate-kube

At this moment there are not many versions of kreate-kube:

• 0.1.0 This version was incomplete and does not work when installed from Pypi
• 0.2.0 This was the first functional version
• 0.3.0 This is the current version, and adds many backward incompatible changes
  • use of a more flat konfig.yaml, with a main app section
  • support for default files to simplify konfig.yaml
  • rename of several patches to remove Patch suffix, and not start with a verb
  • many improvements and cleanup changes

It is expected that new versions will come out regulary:

• fixing bugs
• enhancing command line interface
• adding templates
• improving templates and default values
• improving Python API Some of these enhancements may not be backward compatible. While in 0.x stage there will be only garantuee for backward compatibility between patch versions (e.g. 0.x.1 and 0.x.2)

After the 1.0 release a semantic versioning for backward compatibilty will be used.

In general you should specify a specific version of kreate with a requirements.txt file.

History

This is a rewrite of a similar project written as bash scripts. The bash scripts have been used for deploying over 30 applications to development, acceptance and production environments.

However the bash scripting language was not the best choice, so Python was chosen for several reasons:

• Large bash scripts are difficult to maintain
  • google coding guidelines demand that bash scripts over 100 lines long are to be rewritten in Python. See https://google.github.io/styleguide/shellguide.html#when-to-use-shell, which states:

    if you are writing a script that is more than 100 lines long, or that uses non-straightforward control flow logic, you should rewrite it in a more structured language now. Bear in mind that scripts grow. Rewrite your script early to avoid a more time-consuming rewrite at a later date.

  • not many devops team members are proficient in bash
  • no OO and limited var scoping (most vars are global vars)
• Possibility to run natively on Windows (with Python installed)
  • no CRLF problems
  • Windows can recognizes *.py extension to prevent Linux file permission problems on Windows filesystems
• Much cleaner code
  • yaml parser
  • jinja templates
  • modular design, where a team can add team-specific templates and defaults for their set of applications
  • powerful requirements.txt/pip dependency management