DevOps Notes

# Check OS and kernel uname -a cat /etc/os-release # Linux process list — clean, scriptable ps aux | grep nginx

systemctl status nginx journalctl -u nginx --since "1 hour ago" ss -tlnp | grep :80 chmod 640 /etc/nginx/nginx.conf

#!/bin/bash TOOLS=("git" "docker.io" "ansible" "terraform") for pkg in "${TOOLS[@]}"; do apt-get install -y $pkg && echo "✓ $pkg" done

free -h # RAM available nproc # CPU cores df -h / # Disk space # 8GB RAM = full DevOps lab possible

control-node 192.168.1.10 ├── Ansible + Terraform server-01 192.168.1.11 └── Docker + Compose apps monitor-01 192.168.1.12 └── Prometheus + Grafana

docker run -d -p 80:80 --name web nginx docker ps docker logs web --follow docker exec -it web bash

VM: App → Guest OS → Hypervisor → Host OS Con: App → Docker Engine → Host OS Startup: VM=60s Container=<1s RAM: VM=2GB Container=50MB

version: '3.9' services: postgres: image: postgres:15 volumes: - pgdata:/var/lib/postgresql/data volumes: pgdata: # named — Docker managed

docker network create app-net docker run -d --network app-net --name api myapi docker run -d --network app-net --name db postgres # api resolves db by name: db:5432 docker network inspect app-net

# ❌ Bad FROM ubuntu:latest COPY . . # ✅ Good FROM python:3.11-slim COPY requirements.txt . RUN pip install -r requirements.txt USER appuser

aws ec2 run-instances \ --image-id ami-0c55b159cbfafe1f0 \ --instance-type t3.micro \ --key-name my-key \ --security-group-ids sg-12345 ssh -i my-key.pem ubuntu@PUBLIC_IP

VPC: 10.0.0.0/16 ├── Public: 10.0.1.0/24 ← web+NAT │ ├── EC2 (web server) │ └── NAT Gateway └── Private: 10.0.2.0/24 ← app+db ├── EC2 (app server) └── RDS (database)

Client → ALB (port 443) ├── /api/* → Target Group A ├── /app/* → Target Group B └── /* → Target Group C Health Check: GET /health → 200 OK

# nginx as reverse proxy server { listen 443 ssl; server_name api.devriston.com.pk; location / { proxy_pass http://localhost:3000; proxy_set_header Host $host; } }

HA Architecture — 2 AZ ALB / \ AZ-1 AZ-2 EC2 EC2 RDS ←→ RDS (primary) (standby) Failover: automatic. RTO: ~60s

resource "aws_instance" "web" { ami = "ami-0c55b159cbfafe1f0" instance_type = "t3.micro" tags = { Name = "devriston-web" ManagedBy = "terraform" } }

terraform init # download providers + modules terraform plan # show what will change terraform apply # execute the changes + aws_instance.web will be created Plan: 2 to add, 0 to change, 0 to destroy.

terraform { backend "s3" { bucket = "devriston-tf-state" key = "prod/terraform.tfstate" region = "us-east-1" dynamodb_table = "tf-lock" encrypt = true } }

- name: Install and start Nginx hosts: webservers become: true tasks: - apt: name=nginx state=present - service: name=nginx state=started enabled=yes

name: CI/CD Pipeline on: push: branches: [main] jobs: build-test-deploy: runs-on: ubuntu-latest steps: - docker build → test → push → deploy

Feature GH Actions Jenkins Setup time Minutes Hours/Days Infrastructure Managed Self-hosted Config YAML Groovy DSL Cost Free tier Server cost Marketplace 10,000+ 1,800 plugins

healthcheck: test: ["CMD","curl","-f", "http://localhost:3000/health"] interval: 30s timeout: 10s retries: 3 restart: unless-stopped

git checkout -b feature/add-monitoring # ... make changes ... git add . && git commit -m "feat: prometheus" git push origin feature/add-monitoring # PR → review → merge → CI/CD triggers

Targets (EC2, Docker, Apps) ↓ expose /metrics endpoint Prometheus ← scrapes every 15s ├──→ Grafana (dashboards) └──→ AlertManager (alerts) ↓ Slack / Email / PagerDuty

# CPU usage % across all cores 100 - (avg by(instance)(rate( node_cpu_seconds_total{mode="idle"}[5m] )) * 100) # RAM used % (node_memory_MemTotal_bytes - node_memory_MemAvailable_bytes) / node_memory_MemTotal_bytes * 100

# First checks when something breaks df -h # disk space free -h # memory journalctl -xe --since "10m" # logs ss -tlnp # open ports

Phase 1: Linux + bash + networking + Git Phase 2: Docker + AWS + Terraform Phase 3: Ansible + GitHub Actions Phase 4: Prometheus + Grafana + Loki Phase 5: Kubernetes + Helm + ArgoCD

Effective Learning Loop 1. Pick one concept (Docker networking) 2. Read the docs (not a tutorial) 3. Build a lab (hands-on) 4. Break something (intentionally) 5. Fix it (debug the error) 6. Document on GitHub (portfolio + learning)

Tier 1 — Non-negotiable Linux fundamentals + bash scripting Networking (TCP/IP, DNS, HTTP, TLS) Git + version control workflows Tier 2 — Core DevOps Docker + CI/CD + Cloud + IaC Tier 3 — Differentiators Observability + DevSecOps

Git push → GitHub Actions ├── terraform plan (review) ├── terraform apply (provision) ├── ansible-playbook (configure) └── smoke tests (verify) ↓ Production ↓ Prometheus → Grafana (observe)

# Your very first Python program print("Hello Python") # Output: Hello Python

# Check if Python is already installed python3 --version # Output: Python 3.11.4

# Comments start with # if True: print("Indented = inside the if block") print("Not indented = outside the block")

name = "Devriston" # str (text) age = 25 # int (whole number) price = 99.50 # float (decimal) is_active = True # bool (True/False) print(name, age, price, is_active)

name = input("Enter your name: ") age = int(input("Enter your age: ")) print(f"Hello {name}, you are {age} years old")

x = 10 y = 3 print(x + y) # 13 — addition print(x % y) # 1 — remainder (modulo) print(x > y) # True — comparison

age = 20 if age >= 18: print("Adult") elif age >= 13: print("Teenager") else: print("Child")

for i in range(5): print("Count:", i) # Prints Count: 0 through Count: 4

def greet(name): print(f"Hello, {name}!") greet("Kamran") # Output: Hello, Kamran!

fruits = ["apple", "banana", "mango"] print(fruits[0]) # apple — index starts at 0 fruits.append("grape") print(fruits)