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Horizon Template

What is Horizon Template​

Horizon uses a packaging format called Horizon Template. You can use the Horizon template to deploy various workloads and achieve best practices through a user-friendly form. This document explains the template format and provides basic guidance for building Horizon templates.

Prepare​

Horizon Templates are based on Helm Charts, Json Schema and React JsonSchema Form, so it is important to have a basic understanding of the following knowledge before proceeding:

  • Helm Charts
    Helm charts contain a series of Kubernetes resources that can be used to deploy various simple or complex applications to a Kubernetes cluster.
  • Json Schema
    Json Schema is a declarative language that allows you to annotate and validate JSON documents.
  • React JsonSchema Form
    React JsonSchema Form is a library that generates user-friendly HTML forms based on Json Schema. The form collects user input, which is used to render the chart and generate the final manifest file for deployment to Kubernetes.

Why do we choose React JsonSchema Form​

The values.json.schema specification provided by Helm Chart is mainly for validation, we choose React Json Schema Form mainly because of its stronger form display capabilities. In addition, we applied go template syntax to the json schema file to enhance its flexibility.

Template Structure​

A typical Horizon template is organized as a collection of files that match this:

├── Chart.yaml
├── README.md
├── templates
│   ├── _helpers.tpl
│   └── resource.yaml
│── values.yaml
├── schema
│   ├── application.schema.json
│   └── application.ui.schema.json
└── output
    └── outputs.yaml

It mainly consists of the following parts:

Helm Chart​

Helm chart includes the following files:

├── Chart.yaml
├── README.md
├── templates
│   ├── _helpers.tpl
│   └── resource.yaml
└── values.yaml
  • Chart.yaml
    A standard Helm Chart file that contains meta-information about the chart, such as the chart name, version, and description.

For example:

apiVersion: v2
name: deployment
description: A Horizon Template Chart for kubernets
type: application
version: 0.0.0

  • README.md
    A markdown file that provides documentation and usage instructions for the chart.

    For example:

    # Template name
    template description
    ## Structure
    structure description

  • templates
    A directory contains Go template files that define the Kubernetes resources that will be deployed when the chart is installed. These templates use the values from the values.yaml file and the user input from the form to render the final Kubernetes manifest files.

    • resource.yaml
      The main resource manifest file to applyed to Kubernetes, we recommend you to use a unique name for the name field, such as {{ .Values.horizon.instance }}, for more built-in parameters, please refer to GitOps Repository Structure.

      In addition to the built-in parameters, you can also customize the parameters through the json schema. We recommend putting your parameters in .Values.app.

      For example:

      apiVersion: apps/v1
      kind: Deployment
      metadata:
        name: {{ .Values.horizon.instance }}
      spec:
        replicas: {{ .Values.app.spec.replicas }}
        selector:
        template:
          metadata:
            labels:
            {{- include "podLabels" . | nindent 8 }}
          spec:
            containers:
            - name: {{ .Values.horizon.instance }}
              image: {{ .Values.image }}

    • _helpers.tpl
      An optional file that contains Go template functions that can be reused across different yaml files.

      For example:

      {{- define "podLabels" -}}
      horizoncd.github.io/application: {{ .Values.horizon.application }}
      horizoncd.github.io/instance: {{ .Values.horizon.instance }}
      horizoncd.github.io/environment: {{ .Values.env.environment }}
      {{- end }}

Refer to Helm Chart documentation for more information

Json Schema​

The json schema directory format is as follows:

└── schema
    ├── application.schema.json
    └── application.ui.schema.json

  • application.schema.json
    application.schema.json is used to generate a user-friendly form for users to create application or instance and validate their inputs, it follows the JSON Schema specification, you need to write this file based on the Helm Chart's values.yaml. You can also use Go template syntax in the application.schema.json file to quote admin tags to conditionally show some special options.

    For example, if we set an admin tag maxReplicas=60, the replicas of instance can exceed the default limit of 30. 

    {
      "type": "object",
      "properties": {
        "app": {
          "title": "application",
          "type": "object",
          "properties": {
            "spec": {
              "type": "object",
              "title": "spec",
              "properties": {
                "replicas": {
                  "type": "integer",
                  "title": "replicas",
                  "default": 1,
                  "minimum": 0,
                  "maximum":
                  {{- .maxReplicas | default 30 }}
                },
              },
            }
          }
        }
      }
    }

  • application.ui.schema.json
    The application.ui.schema.json is used to describe the layout and appearance of the form generated by React JsonSchema Form. It can also reference the application.schema.json to customize the form's behavior and appearance.

    For example:

    {
      "ui:order": [
          "app"
      ],
      "app":{
        "ui:order":[
            "spec",
        ],
        "spec": {
          "ui:order":[
            "replicas",
            "*"
          ]
        }
      }
    }

Output​

The output directory includes the following file:

└── output
    └── outputs.yaml

  • outputs.yaml
    It's an optional file that allows the template author to define a set of outputs that can be queried after the template is deployed.

    The following example is to output the generated domain of instance:

    domain:
      description: the domain for the instance
      value: {{ .Values.horizon.instance }}.cloudnative.com

Overall, the Horizon template format allows developers to easily package and distribute Kubernetes-based applications using Helm Charts, while providing a user-friendly form-based input experience using React JsonSchema Form and json schema.

GitOps Repository Structure​

Based on this template, users can create applications and instances through a form on the website. We use GitOps approach to managing the resources that are deployed using the Horizon Template, the directory structure of the gitops repo is as follows:

.
├── Chart.yaml
├── application.yaml
├── manifest.yaml
├── pipeline
│   ├── pipeline-output.yaml
│   └── pipeline.yaml
├── sre
│   └── sre.yaml
├── system
│   ├── env.yaml
│   ├── horizon.yaml
│   └── restart.yaml
└── tags.yaml

  • Chart.yaml
    The gitops repository is also a Helm chart. It relates to the horizon template through the dependencies function in Chart.yaml.

    For example:

    apiVersion: v2
    name: demo
    version: 1.0.0
    dependencies:
    - name: deployment
      version: v0.0.1-ec06d596
      repository: https://horizon-harbor-core.horizon.svc.instance.local/chartrepo/horizon-template

  • application.yaml
    A list of parameters filled in by the user through the form generated by the schema.

    For example:

    deployment:
      app:
        envs:
        - name: test
          value: test
        spec:
          replicas: 1
          resource: x-small

  • manifest.yaml
    The version of the template, which is currently 0.0.2.

    For example

    version: 0.0.2

  • pipeline

    • pipeline-output.yaml
      The pipeline-output file contains the output of CI stage, you can control the output content by customizing the CI script. The default CI script will output the address of the built image and git info.

      ParameterMeaning
      .Values.imageFull path of built image.
      .Values.git.{ref}Git ref of source code. These types of refs are currently supported: branch,tag,commit
      .Values.git.commitIDCommit id of source code
      .Values.git.urlURL of source code

      For example:

      deployment:
        image: library/demo:v1
        git:
          branch: master
          commitID: 28992d8f35a6ef38d59181080b3728df9540d8d6
          url: https://github.com/horizoncd/springboot-source-demo.git

    • pipeline.yaml
      The pipeline.yaml file contains configuration for CI stage, the administrator can customize the json schema of CI stage to extend more build types.

      ParameterMeaning
      .Values.buildTypeBuild type of this instance. "dockerfile" is supported by default.
      .Values.dockerfile.pathPath of dockerfile.
      .Values.dockerfile.contentContent of dockefile
      pipeline:
        buildType: dockerfile
        dockerfile:
          path: ./Dockerfile

  • sre

    • sre.yaml
      In some special situations, SRE can override any parameters in the horizon template's values.yaml through sre.yaml. For example, if we want to schedule an application to nodes with a specific label, we can modify sre.yaml as follows:

      deployment: 
        affinity:
          nodeAffinity:
            requiredDuringSchedulingIgnoredDuringExecution:
              nodeSelectorTerms:
              - matchExpressions:
                - key: cloudnative/demo
                  operator: In
                  values:
                  - "true"

      sre.yaml is generally used to deal with special requirements, while json schema is used to support general requirements.

  • system

    There are some files in the system directory, which contain some parameters that you can refer to in the template.

    • env.yaml

      ParameterMeaning
      .Values.env.environmentEnvironment name
      .Values.env.regionKubernetes name
      .Values.env.namespaceNamespace name
      .Values.env.baseRegistryAddress of image registry
      .Values.env.ingressDomainDomain of ingress

      For example:

      deployment:
        env:
          environment: local
          region: local
          namespace: local-1
          baseRegistry: horizon-harbor-core.horizon.svc.instance.local
          ingressDomain: cloudnative.com

    • horizon.yaml

      ParameterMeaning
      .Values.horizon.applicationApplication name
      .Values.horizon.instanceIDinstance id
      .Values.horizon.instanceinstance name
      .Values.horizon.template.nameTemplate name
      .Values.horizon.template.releaseDomain of ingress
      .Values.horizon.priorityPriority of this instance. you can use it for oversale or preemption.

      For example:

      deployment:
        horizon:
          application: demo
          instanceID: 1
          instance: demo-1
          template:
            name: deployment
            release: v0.0.1-ec06d596
          priority: P0

    • restart.yaml

      ParameterMeaning
      .Values.restartTimeRestart time of instance.You can use it in the resource annotations for rolling update.

      For example:

      deployment:
        restartTime: "2023-01-06 18:28:49"

How to Add a New Template in Horizon​

You can create a new template repository on Github and submit the files according to the above requirements. Then, follow the Template Management Guide to add the new template.