Generate Topics with Templates

Declaring resources one by one gets tedious when you manage dozens of similar topics across teams or regions. In this tutorial you’ll learn Jikkou’s templating by generating a list of topics from a compact data file — a single template plus a few values produces many resources.

By the end you’ll understand the values variable, values files, and how to preview rendered output before applying it.

Prerequisites

• You have completed the Getting Started tutorial.
• You have a running Kafka cluster and a configured Jikkou context.

Step 1 — Define your values

Templating separates data from structure. Put the data in a values file:

file: values.yaml

topicPrefix: "iot-events"
partitions: 6
replicas: 1
countryCodes:
  - fr
  - be
  - de
  - es

Step 2 — Write the template

Now write a template that loops over the data. Templates use Jinja syntax, where {{ ... }} outputs a value and {% ... %} is a control statement. The values from your file are available under the top-level values variable.

file: topics.tpl

apiVersion: "kafka.jikkou.io/v1beta2"
kind: "KafkaTopicList"
items:
{% for country in values.countryCodes %}
  - metadata:
      name: "{{ values.topicPrefix }}-{{ country }}"
    spec:
      partitions: {{ values.partitions }}
      replicationFactor: {{ values.replicas }}
      configs:
        cleanup.policy: "delete"
{% endfor %}

Step 3 — Preview the rendered resources

Always render and inspect the result before touching the cluster. The validate command renders the template and prints the resulting resources:

jikkou validate --files ./topics.tpl --values-files ./values.yaml

You should see four fully-rendered topics — iot-events-fr, iot-events-be, iot-events-de, and iot-events-es — each with 6 partitions.

Step 4 — Apply the generated topics

Once you’re happy with the output, preview the plan and apply it. The same --values-files flag is accepted by diff, apply, create, and update:

jikkou diff  --files ./topics.tpl --values-files ./values.yaml   # preview
jikkou apply --files ./topics.tpl --values-files ./values.yaml   # apply

Add a country to values.yaml, re-run diff, and you’ll see Jikkou plan a single new topic — without touching the template.

Step 5 — Override values from the command line

You can pass or override individual values with --set-value (-v), which is handy in CI pipelines:

jikkou apply --files ./topics.tpl \
  --values-files ./values.yaml \
  --set-value partitions=12

You can also read values from the environment inside the template — for example {{ system.env.TOPIC_PREFIX | default('iot-events', true) }}.

What you learned

• Templating separates data (values files) from structure (the template).
• values exposes your data; {{ }} outputs values and {% %} drives loops and conditions.
• Render and inspect with validate before applying.
• --values-files and --set-value work with diff, apply, and the other reconciliation commands.

Next steps

• Read the Templates concept for two-phase rendering, ConfigMap references, and advanced features.
• Manage multiple schemas the same way using a SchemaRegistrySubjectList — see Manage Schemas.