Template

Tags:

Template helps you to dynamically define resource definition files from external data.

Template Engine

Jikkou provides a simple templating mechanism based-on Jinjava, a Jinja template engine for Java.

Read the official documentation of Jinja to learn more about the syntax and semantics of the template engine.

How Does It Work ?

Jikkou performs the rendering of your template in two phases:

First, an initial rendering is performed using only the values and labels passed through the command-lines arguments.
- Thus, it is perfectly OK if your resource file is not initially a valid YAML file.
Then, a second and final rendering is performed after parsing the YAML resource file using the additional values and labels as defined into the YAML resource file.
- Therefore, it’s important that your resource file is converted into a valid YAML file after the first rendering.

Important

You should use {% raw %}...{% endraw %} tags to ensure the variables defined into the template are not be interpreted during the first rendering.

VariablesCLI-Configuration.md

Jikkou defines a number of top-level variables that are passed to the template engine.

values:
- The values passed into the template through the command-line --values-files and/or --set-value arguments
- In addition, values can be defined into the application.conf file and directly into the template file using the property template.values.
- By default, values is empty.
labels:
- The labels passed into the template through the command-line argument: --set-label.
- In addition, labels can be defined into the template file using the property metadata.labels.
- By default, labels is empty.
system.env:
- This provides access to all environment variables.
system.props:
- This provides access to all system properties.

Template Values

When using templating, a resource definition file may contain the additional property template. fields:

apiVersion: The api version (required)
kind: The resource kind (required)
metadata:
  labels: The set of key/value pairs that you can use to describe your resource file (optional)
  annotations: The set of key/value pairs automatically generated by the tool (optional)
template:
  values: The set of key/value pairs to be passed to the template engine (optional)
spec: Specification of the resource

Values Data File

Values Data File are used to define all the necessary values (i.e., the variables) to be used for generating a template.

Example

# file: ./values.yaml
topicConfigs:
  partitions: 4
  replicas: 3
topicPrefix: "{{ system.env.TOPIC_PREFIX | default('test', true) }}"
countryCodes:
  - fr
  - be
  - de
  - es
  - uk
  - us

Template Resource File

Example

# file: ./kafka-topics.tpl
apiVersion: 'kafka.jikkou.io/v1beta2'
kind: 'KafkaTopicList'
items:
  { % for country in values.countryCodes % }
  - metadata:
      name: "{{ values.topicPrefix}}-iot-events-{{ country }}"
    spec:
      partitions: { { values.topicConfigs.partitions } }
      replicas: { { values.topicConfigs.replicas } }
      configMapRefs:
        - TopicConfig
    { % endfor % }
---
apiVersion: "core.jikkou.io/v1beta2"
kind: "ConfigMap"
metadata:
  name: TopicConfig
template:
  values:
    default_min_insync_replicas: "{{ values.topicConfigs.replicas | default(3, true) | int | add(-1) }}"
data:
  retention.ms: 3600000
  max.message.bytes: 20971520
  min.insync.replicas: '{% raw %}{{ values.default_min_insync_replicas }}{% endraw %}'

Command

$  TOPIC_PREFIX=local jikkou validate --files topics.tpl --values-files values.yaml

(Output)

---
apiVersion: "kafka.jikkou.io/v1beta2"
kind: "KafkaTopicList"
metadata:
  labels: { }
  annotations:
    jikkou.io/resource-location: "file:///tmp/jikkou/topics.tpl"
spec:
  topics:
    - metadata:
        name: "local-iot-events-fr"
      spec:
        partitions: 4
        replicas: 3
        configs:
          min.insync.replicas: "2"
          retention.ms: 3600000
          max.message.bytes: 20971520
    - metadata:
        name: "local-iot-events-be"
      spec:
        partitions: 4
        replicas: 3
        configs:
          min.insync.replicas: "2"
          retention.ms: 3600000
          max.message.bytes: 20971520
    - metadata:
        name: "local-iot-events-de"
      spec:
        partitions: 4
        replicas: 3
        configs:
          min.insync.replicas: "2"
          max.message.bytes: 20971520
          retention.ms: 3600000
    - metadata:
        name: "local-iot-events-es"
      spec:
        partitions: 4
        replicas: 3
        configs:
          min.insync.replicas: "2"
          max.message.bytes: 20971520
          retention.ms: 3600000
    - metadata:
        name: "local-iot-events-uk"
      spec:
        partitions: 4
        replicas: 3
        configs:
          min.insync.replicas: "2"
          max.message.bytes: 20971520
          retention.ms: 3600000
    - metadata:
        name: "local-iot-events-us"
      spec:
        partitions: 4
        replicas: 3
        configs:
          min.insync.replicas: "2"
          max.message.bytes: 20971520
          retention.ms: 3600000

Last modified October 16, 2023: docs(gh-page): update (ce64836f)