Variables, Templates and Handlers

Estimated time: 35 minutes

Overview

Questions

• How does one requirement become a configuration file?
• When should a handler run?

Objectives

• Trace a variable through a template to a managed file.
• Change a listing description and predict handler notification.
• Verify the rendered response and a second converge.

Start from working staging

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From the pointcloud-infra repository root, run pixi run staging-up if staging is stopped. Preserve your existing edits. In this episode change only content/descriptions.yml, and record the original Iceland folder description so you can restore it afterwards.

The role separates inputs (defaults/main.yml and playbook variables), templates (templates/), tasks (tasks/), and handlers (handlers/main.yml). Read ansible/playbooks/group_vars/all.yml: it loads content/descriptions.yml into potree_descriptions. Then read the role’s templates/pointcloud-descriptions.inc.j2 and the “Install listing descriptions” task in tasks/apache.yml.

A template renders variables into text. The template module compares that text with the destination file; if the file changes, this task notifies Reload httpd. Two handlers listen to that name: a configuration syntax check and a reload. Handlers normally run after the play’s tasks and repeated notifications coalesce. The syntax-check handler uses changed_when: false; it still executes.

Challenge

Change one requirement

Requirement: the root listing must describe Iceland as Workshop collection. Change the existing Iceland entry under folders in content/descriptions.yml. Do not add a second folders mapping or edit a generated file in the container.

Before running, predict which task will notify a handler and whether the handler should run on a second converge. Then run:

BASH

pixi run staging-up
curl -ksSf https://localhost:8443/ | grep 'Workshop collection'
podman exec pointcloud-staging apachectl configtest
pixi run staging-up

Record the changed task, handlers, HTTP response, and second recap. Explain why changing this description should reload Apache but editing an ordinary HTML page need not do so. Use -k only for this local self-signed lab.

Show me the solution

Change the entry to Iceland: "Workshop collection". The description template writes /etc/httpd/conf.d/pointcloud-descriptions.inc. Apache must reload to use that configuration. Expect the template to report a change and both listening handlers to run. On the second run, unchanged template output should not notify them. The response check confirms the new description is actually served; a recap alone cannot do that. Ordinary HTML is read as content without a config reload.

If the description is absent, inspect indentation and the exact folder name, then inspect the generated include file. A successful syntax check only proves Apache accepts the configuration, not that the description is correct.

Restore only your description edit and converge again. Run pixi run staging-verify after restoring the original content; the existing verifier checks some specific descriptions. Continue to Organize a role, validate inputs.

Key Points

• Variables carry requirements; templates render them into managed files.
• Changed template output can notify handlers; reporting no change suppresses notification.
• Check the served result as well as configuration syntax.