DevOps Classroom notes 19/Oct/2024

YAML

• This is data representation format
• YAML uses key value or name value pairs to represent data
• values can be of following types
  • simple/scalar
    • text
    • number
    • bool
  • complex
    • list/array
    • map/dictionary/object
• YAML syntax is heavily inspired from python and json (javascript object notation)
• YAML files will have extension of .yaml or .yml
• yaml basic syntax

key: <value>

• Sample YAML

---
title: "Venom The Last Dance" # Text
year: 2024 # number
budget: 110.5 # number
imaxRelease: yes # boolean
genre: # list
  - Action
  - Adventure
  - Fantasy
  - Sci-Fi
starcast: # object
  Venom: Tom Hardy # Text
  Military Member: Chiwetel Ejiofor # Text
  Scientist: Juno Temple # Text

---

Writing Kubernetes Manifests

• Kuberentes manifests are strictly structured by api-references
• Refer Here for reference pages and Refer Here for 1.31 api reference

Hello Pod

• Lets start by writing a pod which will run nginx container
• Refer Here for changeset

---
apiVersion: v1
kind: Pod
metadata:
  name: hello-pod
spec:
  containers:
    - name: web
      image: nginx:1.27

• To create pods from manifest kubectl apply -f <filename.yaml>
• To get basic information

kubectl get pods <pod-name>

• to get little more info

kubectl get pods <pod-name> -o wide

• To get detailed information

kubectl describe pods <pod-name>

• To get podinfo in yaml format

kubectl get pods <pod-name> -o yaml

• To watch the changes

kubectl get pods -w

Create a Pod with two containers

• pod name activity-2
• containers:
  • ngnix
  • alpine with command sleep 1d

---
apiVersion: v1
kind: Pod
metadata:
  name: activity-2
spec:
  containers:
    - name: web
      image: nginx:1.27
    - name: sidecar
      image: alpine
      args: # cmd
        - sleep
        - 1d

• Refer Here

Activity 3: Writing a Pod with a container with exits

• K8s tries restarting pod after crashloopbackoff
  
• Refer Here for changes
• in the arguments lets pass sleep 10s

Init containers

• These represent checking for preconditions

Activity 4:

• Lets write a pod spec with nginx and alpine with sleep 1d
• init containers
  • init1 alpine with sleep 10s
  • init2 alpine with sleep 10s
• Refer Here for spec

Activity 5

• create a pod with
  • container:
    • name: test
    • image: alpine
    • args: sleep 1d
  • we need to pass the following environmental variables
    • USERNAME = admin
    • PASSWORD = admin@123
• equivelent docker commnad

docker run -e "USERNAME=admin" -e "PASSWORD=admin@123" alpine sleep 1d

• Refer Here
  

Lets start adding labels

• Refer Here for official docs
• lets create a pod with nginx container and labels
  • env: dev
  • app: web
  • release: v1.6.9

---
apiVersion: v1
kind: Pod
metadata:
  name: web
  labels:
    env: dev
    app: web
    release: v1.6.9
spec:
  containers:
    - name: web
      image: nginx:1.27

---

Label selectors

• Refer Here for official docs