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GuideDevOps
Lesson 2 of 9

YAML Syntax Basics

Part of the YAML tutorial series.

The Rule of White Space

The most important thing to understand about YAML is that Indentation is everything.

In languages like Java or C++, you use curly braces {} to define blocks of code. In YAML, the number of spaces at the beginning of a line determines which "parent" a "child" belongs to.

No Tabs Allowed!

You must never use tabs in a YAML file. Most modern IDEs (like VS Code) will automatically convert your Tab key into two spaces, but if you accidentally insert a hard Tab character, the YAML parser will crash.

The "Colon Space" Rule

A common mistake for beginners is forgetting the space after the colon.

  • ❌ WRONG: name:GuideDevOps (The parser thinks this is one long string).
  • ✅ RIGHT: name: GuideDevOps (The parser correctly identifies a Key and a Value).

Document Structure

1. The Three Dashes (---)

A YAML file can actually contain multiple separate documents in a single file. This is extremely common in Kubernetes (e.g., putting a Service and a Deployment in one file).

Each document starts with three dashes.

---
# Document 1
name: frontend
---
# Document 2
name: backend

2. The Three Dots (...)

The three dots signify the end of a document. While optional and rarely used in DevOps, you might see them in complex data streams.

Handling Comments

Unlike JSON, YAML supports comments natively using the # symbol.

# This whole line is a comment
replicaCount: 3  # This comment explains why we need 3 pods

Case Sensitivity

YAML is case-sensitive. Active: True is not the same as active: true. Always stick to a consistent casing strategy (usually camelCase or snake_case) for your keys to avoid confusion.

Summary Checklist

  • Use Spaces, not Tabs.
  • Always put a Space after the Colon.
  • Maintain consistent Indentation (usually 2 spaces).
  • Use --- to separate multiple manifests in one file.