Module structure

The source code of the module and its assembly rules must be located in a directory with a certain structure. The best analog is a Helm chart. This page describes the structure of module directories and files.

There is a repository containing the sample module template. We recommend you start your module development with it.

Below is an example of the directory structure of a module created from a template, containing the rules for building and publishing using GitHub Actions:

📁 my-module/
├─ 📁 .github/
│  ├─ 📁 workflows/
│  │  ├─ 📝 build_dev.yaml
│  │  ├─ 📝 build_prod.yaml
│  │  ├─ 📝 checks.yaml
│  │  ├─ 📝 deploy_dev.yaml
│  │  └─ 📝 deploy_prod.yaml
├─ 📁 .werf/
│  ├─ 📁 workflows/
│  │  ├─ 📝 bundle.yaml
│  │  ├─ 📝 images.yaml
│  │  ├─ 📝 images-digest.yaml
│  │  ├─ 📝 python-deps.yaml
│  │  └─ 📝 release.yaml
├─ 📁 charts/
│  └─ 📁 helm_lib/
├─ 📁 crds/
│  ├─ 📝 crd1.yaml
│  ├─ 📝 doc-ru-crd1.yaml
│  ├─ 📝 crd2.yaml
│  └─ 📝 doc-ru-crd2.yaml
├─ 📁 docs/
│  ├─ 📝 README.md
│  ├─ 📝 README.ru.md
│  ├─ 📝 EXAMPLES.md
│  ├─ 📝 EXAMPLES.ru.md
│  ├─ 📝 CONFIGURATION.md
│  ├─ 📝 CONFIGURATION.ru.md
│  ├─ 📝 CR.md
│  ├─ 📝 CR.ru.md
│  ├─ 📝 FAQ.md
│  ├─ 📝 FAQ.ru.md
│  ├─ 📝 ADVANCED_USAGE.md
│  └─ 📝 ADVANCED_USAGE.ru.md
├─ 📁 hooks/
│  ├─ 📝 ensure_crds.py
│  ├─ 📝 hook1.py
│  └─ 📝 hook2.py
├─ 📁 images/
│  ├─ 📁 nginx
│  │  └─ 📝 Dockerfile
│  └─ 📁 backend
│     └─ 📝 werf.inc.yaml
├─ 📁 lib/
│  └─ 📁 python/
│     └─ 📝 requirements.txt
├─ 📁 openapi/
│  ├─ 📁 conversions
│  │  ├─ 📁 testdata
│  │  │  ├─ 📝 v1-1.yaml
│  │  │  └─ 📝 v2-1.yaml
│  │  ├─ 📝 conversions_test.go
│  │  └─ 📝 v2.yaml
│  ├─ 📝 config-values.yaml
│  ├─ 📝 doc-ru-config-values.yaml
│  └─ 📝 values.yaml
├─ 📁 templates/
│  ├─ 📝 a.yaml
│  └─ 📝 b.yaml
├─ 📝 .helmignore
├─ 📝 Chart.yaml
├─ 📝 module.yaml
├─ 📝 werf.yaml
└─ 📝 werf-giterminism.yaml

charts

The /charts directory contains Helm helper charts used when rendering templates.

Deckhouse Kubernetes Platform (DKP) has its own library for working with templates called lib-helm. You can read about the library’s features in the lib-helm repository. To add the library to the module, download the tgz-archive with the appropriate release and move it to the /charts directory of the module.

crds

This directory contains CustomResourceDefinitions (CRDs) used by the module components. CRDs are updated every time the module is started, if there are updates.

For CRDs from the module’s /crds directory to be applied in the cluster, the hello.py hook must be added from the module template. See hooks for more information.

To render CRDs from the /crds directory in the site documentation or documentation module in the cluster, follow these steps:

create a translation file with a structure identical to the original resource file:
- in it, keep only the description parameters containing the translation text;
- use the doc-ru- prefix in the name: e.g., /crds/doc-ru-crd.yaml for /crds/crd.yaml.
create /docs/CR.md and /docs/CR.ru.md files.

docs

The /docs directory contains the module documentation:

README.md — this file describes what the module is for, what problem it solves and outlines the general architectural principles.

The (front matter) file metadata as a YAML structure must present in all language versions of the file. You can use the following parameters in the metadata:
- title — (recommended) The title of the module description page, for example, “Deckhouse web admin console”. It is also used in navigation if linkTitle parameter is not specified.
- menuTitle — (recommended) The name of the module to show in the menu on the left sidebar of the page, e.g., “Deckhouse Admin”. If not set, the name of the directory or repository is used, e.g. deckhouse-admin.
- linkTitle — (optional) Alternative title for navigation if, for example, the title is very long. If not set, the title parameter is used.
- description — (recommended) A short unique description of the page content (up to 150 characters). It should not repeat the `title’. Goes on with the meaning of the title and reveals it in more detail. It is used during generation of preview links and indexing by search engines, e.g., “The module allows you to fully manage your Kubernetes cluster through a web interface with only mouse skills.”
- d8Edition — (optional) ce/be/se/ee. The minimum edition in which the module is available. The default is ce.
- moduleStatus — (optional) experimental. The status of the module. If a module is labeled as experimental, a warning that the code is unstable is displayed on its pages. Also, a special bar in the menu is displayed.
Metadata example
```
---
title: "Deckhouse administrator web console"
menuTitle: "Deckhouse Admin"
description: "The module allows you to fully manage your Kubernetes cluster through a web interface with only mouse skills."
---
```
The EXAMPLES.md file contains examples of module configuration with description.

The (front matter) file metadata as a YAML structure must present in all language versions of the file. You can use the following parameters in the metadata:
- title – (recommended) The title of the page, e.g., Examples. It is also used in navigation if there is no linkTitle.
- description – (recommended) A short unique description of the page content (up to 150 characters). It should not repeat the `title’. Goes on with the meaning of the title and reveals it in more detail. It is used during generation of preview links and indexing by search engines, e.g., “Examples of storing secrets in a neural network and automatically substituting them into thoughts when communicating.”
- linkTitle – (optional) Alternative title for navigation if, for example, the title is very long. If not set, the title parameter is used.
Metadata example
```
---
title: "Examples"
description: "Examples of storing secrets in a neural network with automatic substitution into thoughts when communicating."
---
```
FAQ.md – the file contains frequently asked questions related to module operation, e.g., “What scenario should I choose: A or B?”.

The (front matter) file metadata as a YAML structure must present in all language versions of the file. You can use the following parameters in the metadata:
- title – (recommended) The title of the page.
- description – (recommended) A short unique description of the page content (up to 150 characters).
- linkTitle – (optional) Alternative title for navigation if, for example, the title is very long. If not set, the title parameter is used.
Metadata example
```
---
title: "FAQs"
description: "Frequently asked questions."
---
```
ADVANCED_USAGE.md — this file contains instructions for debugging the module.

The (front matter) file metadata as a YAML structure must present in all language versions of the file. You can use the following parameters in the metadata:
- title – (recommended) The title of the page.
- description – (recommended) A short unique description of the page content (up to 150 characters).
- linkTitle – (optional) Alternative title for navigation if, for example, the title is very long. If not set, the title parameter is used.
Metadata example
```
---
title: "Module debugging"
description: "This section covers all the steps for debugging the module."
---
```
Manually add CR.md and CR.ru.md, the files for generating resources from the /crds/ directory.
Metadata example
```
---
title: "Custom resources"
---
```
Manually add CONFIGURATION.md, the file to create resources from /openapi/config-values.yaml and /openapi/doc-<LANG>-config-values.yaml.
Metadata example
```
---
title: "Module settings"
---
```

All images, PDF files and other media files should be stored in the /docs directory or its subdirectories (e.g, /docs/images/). All links to files should be relative.

You need a file with the appropriate suffix for each language, e.g. image1.jpg and image1.ru.jpg. Here’s how you can include images in your document:

[image1](image1.jpg) in an English-language document;
[image1](image1.ru.jpg) in a Russian-language document.

hooks

The /hooks directory contains the module’s hooks. A hook is an executable file executed in response to an event. Hooks are also used by the module for dynamic interaction with Kubernetes API. For example, they can be used to handle events related to the creation or deletion of objects in a cluster. Get to know the concept of hooks before you start developing your own hook. You can use the Python library by the Deckhouse team to speed up the development of hooks.

Hook requirements:

The hook must be written in the Python language.
When run with the --config parameter, the hook must output its configuration in YAML format.
When run without parameters, the hook must perform its intended action.

The hook files must be executable. Add the appropriate permissions using the chmod +x <path to the hook file> command.

You can find example hooks in the module template repository.

Below is an example of a hook that enables CRDs (from the /crds directory of the module):

import os

import yaml
from deckhouse import hook

# We expect structure with possible subdirectories like this:
#
#   my-module/
#       crds/
#           crd1.yaml
#           crd2.yaml
#           subdir/
#               crd3.yaml
#       hooks/
#           ensure_crds.py # this file

config = """
configVersion: v1
onStartup: 5
"""


def main(ctx: hook.Context):
    for crd in iter_manifests(find_crds_root(__file__)):
        ctx.kubernetes.create_or_update(crd)


def iter_manifests(root_path: str):
    if not os.path.exists(root_path):
        return

    for dirpath, dirnames, filenames in os.walk(top=root_path):
        for filename in filenames:
            if not filename.endswith(".yaml"):
                # Seek only manifests.
                continue
            if filename.startswith("doc-"):
                # Skip YAML files for module documentation.
                continue

        crd_path = os.path.join(dirpath, filename)
        with open(crd_path, "r", encoding="utf-8") as f:
            for manifest in yaml.safe_load_all(f):
                if manifest is None:
                    continue
                yield manifest

    for dirname in dirnames:
        subroot = os.path.join(dirpath, dirname)
        for manifest in iter_manifests(subroot):
            yield manifest


def find_crds_root(hookpath):
    hooks_root = os.path.dirname(hookpath)
    module_root = os.path.dirname(hooks_root)
    crds_root = os.path.join(module_root, "crds")
    return crds_root


if __name__ == "__main__":
    hook.run(main, config=config)

images

The /images directory contains instructions for building module container images. The first level contains directories for files used to create the container image, the second level contains the building context.

There are two ways to define a container image:

Dockerfile — this file contains commands for building images. To build an application from source code, copy it next to the Dockerfile and include it in the image using the COPY command.
The werf.inc.yaml file, which is the same as the image definition section in werf.yaml.

The image name matches the directory name for this module, written in camelCase notation starting with a small letter. For example, the directory /images/echo-server corresponds to the image name echoServer.

The built images have content-based tags that can be used when building other images. To use content-based image tags, enable the lib-helm library. You can also use other features of the helm_lib library of Deckhouse Kubernetes Platform.

Below is an example of using a content-based image tag in a Helm chart:

image: {{ include "helm_lib_module_image" (list . "<image name>") }}

openapi

conversions

The /openapi/conversions directory contains module parameter conversion files and their tests.

Module parameter conversions allow you to convert the OpenAPI specification of module parameters from one version to another. Conversions may be necessary when a parameter is renamed or moved to a different location in a new version of the OpenAPI specification.

Each conversion can only be performed between two consecutive versions (e.g., from the first to the second one). There can be several conversions, and the chain of conversions must cover all versions of the parameter specification with no “gaps”.

The conversion file is an arbitrarily named YAML file of the following format:

version: N # The version number to convert to. 
conversions: []  # A set of jq expressions to transform data from the previous version.

Below is an example of a module parameter conversion file where in version 2, the .auth.password parameter has been removed:

version: 2
conversions:
  - del(.auth.password) | if .auth == {} then del(.auth) end

Conversion tests

You can use the conversion.TestConvert function to write conversion tests. It receives the following parameters:

path to the source configuration file (i.e., the version before the conversion);
path to the resulting configuration file (i.e., the version after the conversion).

An example of a conversion test.

templates

The /templates directory contains Helm templates.

Use the path .Values.<moduleName> to access module settings in templates, and .Values.global for global settings. The module name is converted to camelCase notation.
To facilitate working with templates, use lib-helm, which is a set of extra functions that make it easier to work with global and module values.
Accesses to the registry from the ModuleSource resource are available at the .Values.<moduleName>.registry.dockercfg path.

To use these functions to pull image pools in controllers, create a secret and add it to the corresponding parameter: "imagePullSecrets": [{"name":"registry-creds"}].

apiVersion: v1
kind: Secret
metadata:
  name: registry-creds
type: kubernetes.io/dockerconfigjson
data:
  .dockerconfigjson: {{ .Values.<moduleName>.registry.dockercfg }}

A module can have parameters with which it can alter its behavior. Module parameters and their validation scheme are described in OpenAPI-schemes in /openapi directory.

The settings are stored in two files: config-values.yaml and values.yaml.

You can find an example of an OpenAPI schema in module template.

config-values.yaml

This file is required to validate the module parameters that the user can configure via ModuleConfig.

To render the schema in the documentation on the site or in the documentation module in the cluster, create:

the doc-ru-config-values.yaml file with a structure similar to that of the config-values.yaml file. Keep only the translated description parameters in the doc-ru-config-values.yaml file;
the /docs/CONFIGURATION.md and /docs/CONFIGURATION.ru.md files to enable rendering of data from the /openapi/config-values.yaml and /openapi/doc-ru-config-values.yaml files.

An example of a /openapi/config-values.yaml schema with a single configurable nodeSelector parameter:

type: object
properties:
  nodeSelector:
    type: object
    additionalProperties:
      type: string
    description: |
      The same as the Pods' `spec.nodeSelector` parameter in Kubernetes.

      If the parameter is omitted or `false`, `nodeSelector` will be determined
      [automatically](https://deckhouse.io/products/kubernetes-platform/documentation/v1/#advanced-scheduling).</code>

An example of the /openapi/doc-ru-config-values.yaml file for the Russian translation of the schema:

properties:
  nodeSelector:
    description: |
      Russian description. Markdown markup.</code>

values.yaml

This file is required for validating the source data when rendering templates without using extra Helm chart functions. Its closest analogs are Helm’s schema files.

You can automatically add parameter validation from config-values.yaml to values.yaml. In this case, the basic values.yaml looks as follows:

x-extend:
  schema: config-values.yaml
type: object
properties:
  internal:
    type: object
    default: {}

.helmignore

.helmignore allows you to exclude files from the Helm release. In case of DKP modules, directories /crds, /images, /hooks, /openapi must be added to .helmignore to avoid exceeding 1 Mb limit of Helm release size.

Chart.yaml

This is a mandatory file for a chart, similar to Chart.yaml in Helm. It must contain at least a name parameter with the module name and a version parameter with the version.

An example:

name: echoserver
version: 0.0.1
dependencies:
- name: deckhouse_lib_helm
  version: 1.5.0
  repository: https://deckhouse.github.io/lib-helm

module.yaml

This file stores the following module settings:

tags: string — the additional module tags, which are converted to module labels: module.deckhouse.io/$tag="".
weight: integer — the module weight. The default weight is 900, you can set your own weight between 900 and 999.
stage: string — module lifecycle stage. Can be Sandbox, Incubating, Graduated, or Deprecated.
description: string — the module description.

An example:

tags: ["test", "myTag"]
weight: 960
stage: "Sandbox"
description: "my awesome module"

Applying this file will create a module (deckhouse.io/v1alpha/Module) with the labels module.deckhouse.io/test="" and module.deckhouse.io/myTag="", weight 960, and the description my awesome module.

This way you can control the module sequence as well as specify additional meta-information for the modules.

charts

crds

docs

hooks

images

openapi

conversions

Conversion tests

templates

config-values.yaml

values.yaml

.helmignore

Chart.yaml

module.yaml

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