Cloud computing delivers computing resources (servers, storage, networking, software) over the internet on a pay-as-you-go model.
graph TD
subgraph IaaS["IaaS — Infrastructure as a Service"]
VM["Virtual Machines\nStorage, Networking\nYou manage: OS + everything above"]
end
subgraph PaaS["PaaS — Platform as a Service"]
PLAT["Runtime, Middleware, DB\nYou manage: App + Data only"]
end
subgraph SaaS["SaaS — Software as a Service"]
APP["Full application\nYou manage: nothing (just use it)"]
end
IaaS --> PaaS --> SaaS
IaaS_EX["Examples:\nAWS EC2, Azure VMs\nGoogle Compute Engine\nDigitalOcean Droplets"]
PaaS_EX["Examples:\nAWS Elastic Beanstalk\nHeroku, Google App Engine\nAzure App Service"]
SaaS_EX["Examples:\nGmail, Office 365\nSalesforce, Slack\nGitHub"]
| Model | Description | Example |
|---|---|---|
| Public Cloud | Shared infrastructure, pay-per-use | AWS, Azure, GCP |
| Private Cloud | Dedicated infrastructure for one org | On-prem VMware, OpenStack |
| Hybrid Cloud | Mix of public + private | On-prem + AWS with VPN |
| Multi-Cloud | Multiple public providers | AWS + Azure |
A VM is a software emulation of a physical computer. Multiple VMs run on one physical host via a hypervisor.
Physical Host
├── Hypervisor (Type 1: ESXi, Hyper-V, KVM)
│ ├── VM 1: Ubuntu Server (2 vCPU, 4 GB RAM)
│ ├── VM 2: Windows Server (4 vCPU, 8 GB RAM)
│ └── VM 3: CentOS (1 vCPU, 2 GB RAM)
Type 1 Hypervisor = Bare metal (runs directly on hardware) — production
Type 2 Hypervisor = Hosted (runs on top of OS) — VirtualBox, VMware Workstation
# Check if KVM supported
egrep -c '(vmx|svm)' /proc/cpuinfo # >0 means yes
# Install KVM + management tools
sudo apt install qemu-kvm libvirt-daemon-system virtinst virt-manager
# Create VM from CLI
virt-install \
--name ubuntu-server \
--ram 2048 \
--vcpus 2 \
--disk path=/var/lib/libvirt/images/ubuntu.qcow2,size=20 \
--cdrom /tmp/ubuntu-22.04-server.iso \
--network bridge=virbr0 \
--graphics none \
--console pty,target_type=serial \
--os-variant ubuntu22.04
# Manage VMs
virsh list --all # List VMs
virsh start ubuntu-server # Start VM
virsh shutdown ubuntu-server # Graceful shutdown
virsh destroy ubuntu-server # Force stop
virsh suspend ubuntu-server # Pause
virsh resume ubuntu-server # Resume
virsh snapshot-create-as ubuntu-server snap1 # SnapshotContainers are lightweight, portable, isolated environments that share the host OS kernel (unlike VMs which emulate full hardware).
Virtual Machine: Container:
┌──────────────────┐ ┌──────────────────┐
│ App A │ │ App A │
│ Libraries │ │ Libraries │
│ Guest OS │ ├──────────────────┤
├──────────────────┤ │ App B │
│ App B │ │ Libraries │
│ Libraries │ ├──────────────────┤
│ Guest OS │ │ Container Runtime│
├──────────────────┤ │ (Docker Engine) │
│ Hypervisor │ ├──────────────────┤
├──────────────────┤ │ Host OS Kernel │
│ Hardware │ ├──────────────────┤
└──────────────────┘ │ Hardware │
└──────────────────┘
Startup: minutes Startup: seconds
Size: GBs Size: MBs
Isolation: Full OS Isolation: Process-level
# Install Docker
curl -fsSL https://get.docker.com | sh
sudo usermod -aG docker $USER # Add user to docker group (re-login)
# Images
docker pull ubuntu:22.04 # Download image
docker images # List local images
docker rmi ubuntu:22.04 # Remove image
# Containers
docker run ubuntu:22.04 echo "hello" # Run command in container
docker run -it ubuntu:22.04 bash # Interactive shell
docker run -d -p 8080:80 nginx # Detached, port mapping
docker run --name myapp -d nginx # Named container
# Flags:
# -d = detached (background)
# -it = interactive terminal
# -p host:container = port mapping
# --name = container name
# -v /host:/container = volume mount
# -e VAR=val = environment variable
# --rm = remove on exit
# Container management
docker ps # Running containers
docker ps -a # All containers
docker stop myapp # Stop
docker start myapp # Start stopped container
docker restart myapp # Restart
docker rm myapp # Remove container
docker logs myapp # View logs
docker logs -f myapp # Follow logs
docker exec -it myapp bash # Shell into running container
docker inspect myapp # Full container info
docker stats # Live resource usage
# Dockerfile
cat > Dockerfile << 'EOF'
FROM node:18-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
EXPOSE 3000
CMD ["node", "server.js"]
EOF
docker build -t myapp:1.0 . # Build image
docker build -t myapp:1.0 -f Dockerfile.prod .
# Docker Compose
docker compose up -d # Start all services
docker compose down # Stop and remove
docker compose logs -f # Follow logs
docker compose ps # StatusSSH provides encrypted remote terminal access to Linux/Unix systems.
See also: Networking Fundamentals → (Port 22)
# Basic connection
ssh username@hostname
ssh username@192.168.1.100
ssh -p 2222 username@host # Custom port
ssh -i ~/.ssh/id_rsa username@host # Specific key
ssh -v username@host # Verbose (debug connection)
# SSH config file (~/.ssh/config) — simplify connections
Host myserver
HostName 192.168.1.100
User alice
Port 22
IdentityFile ~/.ssh/id_rsa_myserver
ServerAliveInterval 60
# Now just:
ssh myserver# Generate key pair
ssh-keygen -t ed25519 -C "alice@laptop" # Modern (recommended)
ssh-keygen -t rsa -b 4096 -C "alice@laptop" # RSA 4096-bit
# Files created:
# ~/.ssh/id_ed25519 (private key — keep secret!)
# ~/.ssh/id_ed25519.pub (public key — share this)
# Copy public key to server
ssh-copy-id alice@192.168.1.100
ssh-copy-id -i ~/.ssh/id_ed25519.pub alice@192.168.1.100
# Manual copy (if ssh-copy-id not available)
cat ~/.ssh/id_ed25519.pub | ssh alice@host "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"
# Key permissions (MUST be correct or SSH refuses)
chmod 700 ~/.ssh/
chmod 600 ~/.ssh/id_ed25519 # Private key
chmod 644 ~/.ssh/id_ed25519.pub # Public key
chmod 600 ~/.ssh/authorized_keys
chmod 600 ~/.ssh/config# Config file: /etc/ssh/sshd_config
# Recommended security settings:
Port 22 # Change to non-standard (e.g., 2222)
PermitRootLogin no # Disable root login
PasswordAuthentication no # Keys only (after copying your key!)
PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
MaxAuthTries 3
AllowUsers alice bob # Whitelist users
X11Forwarding no
# Apply changes
sudo systemctl restart sshd# Local port forwarding: access remote service locally
# Access remote MySQL (3306) via localhost:3307
ssh -L 3307:localhost:3306 user@remotehost
# Now connect to: mysql -h 127.0.0.1 -P 3307
# Remote port forwarding: expose local service remotely
# Expose local port 8080 on remote's port 80
ssh -R 80:localhost:8080 user@remotehost
# Dynamic port forwarding (SOCKS proxy)
ssh -D 1080 user@remotehost
# Configure browser to use SOCKS5 proxy at 127.0.0.1:1080
# Jump host / Bastion host
ssh -J bastion@jumphost user@private-server
# Config file version:
# Host private-server
# ProxyJump bastion@jumphost# SCP — Secure Copy
scp file.txt alice@host:/remote/path/
scp alice@host:/remote/file.txt ./local/
scp -r local_dir/ alice@host:/remote/ # Recursive
scp -P 2222 file.txt alice@host:/path/ # Custom port
# SFTP — Interactive FTP over SSH
sftp alice@host
# Commands inside sftp:
# ls, cd, mkdir, rm, rmdir
# lls, lcd (local)
# put localfile remotefile (upload)
# get remotefile localfile (download)
# mput *.txt (upload multiple)
# mget *.txt (download multiple)
# bye / exit / quitRDP provides graphical remote access to Windows machines on port 3389.
# Enable RDP on Windows (PowerShell)
Set-ItemProperty -Path 'HKLM:\System\CurrentControlSet\Control\Terminal Server' -Name "fDenyTSConnections" -Value 0
Enable-NetFirewallRule -DisplayGroup "Remote Desktop"
# Disable RDP
Set-ItemProperty -Path 'HKLM:\System\CurrentControlSet\Control\Terminal Server' -Name "fDenyTSConnections" -Value 1
# Check if RDP is enabled
(Get-ItemProperty -Path 'HKLM:\System\CurrentControlSet\Control\Terminal Server').fDenyTSConnections
# 0 = enabled, 1 = disabled# Connect to RDP from Linux
sudo apt install freerdp2-x11
xfreerdp /v:192.168.1.100 /u:alice /p:password
xfreerdp /v:host /u:alice /p:pass /f # Fullscreen
xfreerdp /v:host:3389 /u:alice /cert-ignore # Ignore cert warning
# Remmina (GUI RDP client)
sudo apt install remmina remmina-plugin-rdp# Install AWS CLI
curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o awscliv2.zip
unzip awscliv2.zip && sudo ./aws/install
# Configure
aws configure
# AWS Access Key ID: AKIA...
# AWS Secret Access Key: ...
# Default region: ap-south-1
# Default output format: json
# Common commands
aws ec2 describe-instances # List EC2 instances
aws ec2 start-instances --instance-ids i-xxx # Start instance
aws ec2 stop-instances --instance-ids i-xxx # Stop instance
aws s3 ls # List S3 buckets
aws s3 cp file.txt s3://mybucket/ # Upload to S3
aws s3 sync ./local/ s3://mybucket/ # Sync directory
aws s3 rb s3://mybucket --force # Delete bucket
aws logs tail /aws/lambda/myfunction --follow # CloudWatch logs
# SSH to EC2
ssh -i ~/.ssh/mykey.pem ec2-user@ec2-ip-addr.compute.amazonaws.com- Networking Fundamentals ← — ports 22, 3389
- Security Concepts ← — encryption, firewall
- VPN ← — tunneling
- Software Installation ← — installing cloud tools
- Troubleshooting →