Kubernator

Kubernator™ (Ktor™) is an integrated solution for the Kubernetes state management. It operates on directories, processing their content via a collection of plugins, generating Kubernetes resources in the process, validating them, transforming them and then applying against the Kubernetes cluster.

Notices

Beta Software

While fully functional in the current state and used in production, this software is in BETA. A lot of things are expected to change rapidly, including main APIs, initialization procedures and some core features. Documentation at this stage is basically non-existent.

License

The product is licensed under the Apache License, Version 2.0. Please see LICENSE for further details.

Warranties and Liability

Kubernator and its plugins are provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. You are solely responsible for determining the appropriateness of using or redistributing Kubernator and assume any risks associated with doing so.

Trademarks

"Kubernator" and "Ktor" are trademarks or registered trademarks of Express Systems USA, Inc and Karellen, Inc. All other trademarks are property of their respective owners.

Problem Statement

Solution

Using Kubernator with Docker

A simple example is as follows:

$ docker run --mount type=bind,source="$(pwd)",target=/root,readonly -t ghcr.io/karellen/kubernator:latest

Using Kubernator on MacOS

$ brew install python3.11
$ pip3.11 install 'kubernator~=1.0.9'
$ kubernator --version

Please note, that some plugins (e.g. awscli, eks) may require additional volume mounts or environmental variables to be passed for credentials and other external configuration.

Mode of Operation

Kubernator is a command line utility. Upon startup and processing of the command line arguments and initializing logging, Kubernator initializes plugins. Current plugins include:

0. Kubernator App
1. Terraform
2. kOps
3. Kubernetes
4. Helm
5. Template

The order of initialization matters as it's the order the plugin handlers are executed!

The entire application operates in the following stages by invoking each plugin's stage handler in sequence:

1. Plugin Init Stage
2. Pre-start script (if specified)
3. Plugin Start Stage
4. For each directory in the pipeline:
   1. Plugin Before Directory Stage
   2. If .kubernator.py is present in the directory:
      1. Plugin Before Script Stage
      2. .kubernator.py script
      3. Plugin After Script Stage
   3. Plugin After Directory Stage
5. Plugin End Stage

Each plugin individually plays a specific role and performs a specific function which will be described in a later section.

State/Context

There is a global state that is carried through as the application is running. It is a hierarchy of objects (context) that follows the parent-child relationship as the application traverses the directory structure. For example, given the directory structure /a/b, /a/c, and /a/c/d any value of the context set or modified in context scoped to directory /a is visible in directories /a/b, /a/c and /a/c/d, while the same modified or set in /a/b is only visible there, while one in /a/c is visible in /a/c and in /a/c/d but not /a or /a/b.

Additionally, there is a context.globals which is the top-most context that is available in all stages that are not associated with the directory structure.

Note, that in cases where the directory structure traversal moves to remote directories (that are actualized by local temporary directories), such remote directory structure enters the context hierarchy as a child of the directory in which remote was registered.

Also note, that context carries not just data by references to essential functions.

In pre-start and .kubernator.py scripts the context is fully available as a global variable ktor.

Plugins

Kubernator App Plugin

The role of the Kubernator App Plugin is to traverse the directory structure, expose essential functions through context and to run Kubernator scripts.

In the After Directory Stage Kubernator app scans the directories immediately available in the current, sorts them in the alphabetic order, excludes those matching any of the patterns in context.app.excludes and then queues up the remaining directories in the order the match the patterns in context.app.includes.

Thus, for a directory content /a/foo, /a/bal, /a/bar, /a/baz, excludes f*, and includes baz and *, the resulting queue of directories to traverse will be /a/baz, /a/bal, /a/bar.

Notice, that user can further interfere with processing order of the directory queue by asking Kubernator to walk arbitrary paths, both local and remote.

Context

• ktor.app.args

  Namespace containing command line argument values

• ktor.app.walk_local(*paths: Union[Path, str, bytes])

  Immediately schedules the paths to be traversed after the current directory by adding them to the queue Relative path is relative to the current directory

• ktor.app.walk_remote(repo, *path_prefixes: Union[Path, str, bytes])

  Immediately schedules the path prefixes under the remote repo URL to be traversed after the current directory by adding them to the queue. Only Git URLs are currently supported. All absolute path prefixes are relativized based on the repository.

• ktor.app.repository_credentials_provider(func: Callable)

  Sets a repository credentials provider function func that sets/overwrites credentials for URLs being specified by walk_remote. The callable func accepts a single argument containing a parsed URL in a form of tuple. The func is expected to return a tuple of three elements representing URL schema, username and password. If the value should not be changed it should be None. To convert from git://repo.com/hello to HTTPS authentication one should write a function returning ("https", "username", "password"). The best utility is achieved by logic that allows running the plan both in CI and local environments using different authentication mechanics in different environments.

Terraform

This is exclusively designed to pull the configuration options out of Terraform and to allow scripts and plugins to utilize that data.

Context

• ktor.tf

  A dictionary containing the values from Terraform output

Kops

Context

Kubernetes

Context

Helm

Context

Templates

Context

Examples

Adding Remote Directory

ktor.app.repository_credentials_provider(lambda r: ("ssh", "git", None))
ktor.app.walk_remote("git://repo.example.com/org/project?ref=dev", "/project")

Adding Local Directory

ktor.app.walk_local("/home/username/local-dir")

Using Transformers

def remove_replicas(resources, r: "K8SResource"):
    if (r.group == "apps" and r.kind in ("StatefulSet", "Deployment")
            and "replicas" in r.manifest["spec"]):
        logger.warning("Resource %s in %s contains `replica` specification that will be removed. Use HPA!!!",
                       r, r.source)
        del r.manifest["spec"]["replicas"]


ktor.k8s.add_transformer(remove_replicas)