Stop 05 · Scripting & Programming for DevOpsTopics · 6/8

YAML & Config File Fundamentals

In short

GitHub Actions, Kubernetes, Ansible, Docker Compose: all YAML. One wrong space and the pipeline fails with a confusing error. Learn the rules once and save yourself many late nights.

YAML is the near-universal configuration format across DevOps tools — CI/CD pipelines, Kubernetes manifests, Ansible playbooks — understanding its indentation-sensitive syntax prevents a huge share of frustrating errors.

The mascot at a vegetable market holds a long shopping list with neatly indented scribbled lines.

Think of it like this

Mummy's grocery list

Mummy writes 'Vegetables' and indents onions and tomatoes under it, then 'Dairy' with milk and paneer under that. The indent alone tells you what belongs where. YAML works exactly like that, so shifting one line by a space moves paneer into the vegetable bag.

Watch it happen

How YAML indentation nests data

config

service: payments

ports:

- 8080

database:

host: db.internal

port: 5432

1/4Top-level keys sit at column zero. service is a simple key: value pair.

The big ideas

What you need to know

Spaces only, never tabs

YAML forbids tabs for indentation. Set your editor to insert two spaces when you press Tab.

Quote risky values

1.10 becomes the number 1.1, and in older YAML parsers NO can become false. Quote versions and codes.

Maps and lists

key: value makes a map. - item makes a list. Kubernetes files are mostly maps holding lists of maps.

Lint before you push

yamllint or your editor's YAML extension catches bad indentation before CI or kubectl does.

See it in code

Walk through the code

yaml

1service: payments2replicas: 33debug: false4version: "1.10"     # quoted, or YAML reads it as the number 1.15ports:6  - 80807  - 90908database:9  host: db.internal10  port: 543211env:12  - name: LOG_LEVEL13    value: info14notes: |15  Multi-line text keeps16  its line breaks.

1/4Simple values: a string, a number, a boolean and a version quoted so it stays a string.

Run yamllint file.yaml or python3 -c "import yaml,sys; print(yaml.safe_load(open(sys.argv[1])))" file.yaml to see how a parser reads it.

Save yourself the pain

Common mistakes

Oops

Mixing tabs and spaces, or 2 and 4 spaces, in the same file.

Do this instead

Use two spaces everywhere, turn on 'show whitespace' in your editor, and lint before committing.

Oops

Writing version: 1.10 or country: NO without quotes.

Do this instead

Quote anything that must stay text: versions, zip codes, country codes and strings like yes or on.

Your mission

Find the YAML bugs

~20 min

Quick check

Your config has version: 1.10 without quotes. What does a YAML parser give your app?

Go deeper

1Write a small YAML file and validate it with an online or CLI YAML linter.
2Learn common YAML pitfalls: inconsistent indentation, tabs vs spaces, and quoting rules.
3Compare the same configuration expressed in YAML versus JSON to see the readability trade-off.