Terminal, Git, and YAML essentials

This primer supplies the small amount of syntax that later chapters rely on. You may skim it now and return when a command or manifest feels unfamiliar.

Read a shell command before running it

The prompt is not part of a command. Run commands from the directory named by the lab. A relative path such as stages/stage1 starts at your current working directory; pwd prints that directory and ls lists its contents.

Shell symbols change behaviour:

Syntax	Meaning
command --flag value	Run a program with an option and its value.
`a	b`
a && b	Run b only if a succeeds.
> file	Replace a file with command output. Treat this as destructive.
<name>	A placeholder in these docs; replace it, including the brackets.

Stop if a command targets a cluster, namespace, file, or volume you did not expect. Use Ctrl+C to stop a foreground watch or port-forward.

Record the lab revision with Git

Git identifies an exact repository state with a commit hash. git status shows local changes; git rev-parse HEAD prints the current commit. Changing commits can overwrite local work, so use a clean, dedicated lab clone.

git status --short
git rev-parse HEAD

The lab compatibility contract provides the supported clone and checkout commands.

Read YAML as nested data

YAML uses indentation to express structure. Spaces matter; tabs should not be used. A mapping associates keys with values, while a sequence begins each item with -.

A small Pod request

apiVersion: v1                 # mapping key and scalar value
kind: Pod
metadata:                     # nested mapping
  name: booking
  labels:
    app: booking
spec:
  containers:                 # sequence
    - name: booking
      image: example/booking:1.0
      ports:
        - containerPort: 8082

Read a Kubernetes manifest in four passes:

1. apiVersion and kind: what type of object is requested?
2. metadata: what is it called, where does it live, and which labels identify it?
3. spec: what desired state is requested?
4. references and selectors: which other names or labels must match exactly?

YAML order usually does not mean execution order. A valid-looking manifest can still reference a missing name, use an unsupported field, or request something the cluster cannot provide. API acceptance is only the first evidence rung.

Check your understanding

If containers: is followed by two lines beginning with - name:, what does that represent?

A sequence containing two container definitions. The dash creates each list item; indentation shows that both belong to containers.

Does a successful kubectl apply prove that the application works?

No. It proves that the API accepted the request. Controllers must still converge, Pods must become useful, and the passenger path must be verified.

Continue to Meet Apollo Airlines, the application whose request path will connect every later concept.