Linux: Git, Containers and Automation for DevOps

# Generate dedicated Ed25519 keypair for Git operations
ssh-keygen -t ed25519 -C "devops@example.com" -f ~/.ssh/id_ed25519_git

# Print public key to copy into GitHub/GitLab account settings
cat ~/.ssh/id_ed25519_git.pub

# Test authenticated SSH connectivity to remote provider
ssh -T git@github.com

# Configure repository remote URL to use SSH
git remote set-url origin git@github.com:organization/infra-repo.git

# Run container in background with port mapping and volume mount
docker run -d \
  --name webapp \
  -p 8080:80 \
  -v app_data:/usr/share/nginx/html \
  --restart unless-stopped \
  nginx:alpine

# Review running containers, resource usage, and streaming logs
docker ps
docker stats --no-stream
docker logs -f webapp

# Write compose.yaml
cat > compose.yaml <<'YAML'
services:
  web:
    build: .
    ports:
      - "80:8000"
    environment:
      - DB_HOST=db
    depends_on:
      - db

  db:
    image: postgres:15-alpine
    environment:
      POSTGRES_PASSWORD: secret
    volumes:
      - pgdata:/var/lib/postgresql/data

volumes:
  pgdata:
YAML

# Validate and start the stack
docker compose config
docker compose up -d

# Write the inventory
cat > hosts.ini <<'INI'
[webservers]
web01.internal ansible_host=10.0.1.10
web02.internal ansible_host=10.0.1.11
INI

# Write the playbook
cat > site.yml <<'YAML'
---
- name: Configure Production Web Servers
  hosts: webservers
  become: true
  tasks:
    - name: Ensure Nginx package is installed
      ansible.builtin.apt:
        name: nginx
        state: present
        update_cache: true

    - name: Ensure deployment user exists
      ansible.builtin.user:
        name: deployer
        shell: /bin/bash
        groups: sudo
        append: true

    - name: Ensure Nginx service is running and enabled at boot
      ansible.builtin.service:
        name: nginx
        state: started
        enabled: true
YAML

# Execute playbook against inventory
ansible-playbook -i hosts.ini site.yml

# Write the cloud-init user data
cat > user-data.yaml <<'CLOUD'
#cloud-config
package_upgrade: true
packages:
  - curl
  - git
  - ufw

users:
  - name: devops
    sudo: ALL=(ALL) NOPASSWD:ALL
    shell: /bin/bash
    ssh_authorized_keys:
      - ssh-ed25519 AAAAC3NzaC1l... admin@laptop

runcmd:
  - ufw default deny incoming
  - ufw allow 22/tcp
  - ufw --force enable
CLOUD

# Validate the schema
cloud-init schema --config-file user-data.yaml

# Write the disk check script
cat > disk_check.py <<'PY'
#!/usr/bin/env python3
import subprocess
import json
import sys

def check_disk_space(threshold_percent=80):
    """Inspect disk usage and return warning if threshold is breached."""
    cmd = ["df", "--output=pcent,target", "/"]
    result = subprocess.run(cmd, capture_output=True, text=True, check=True)
    
    # Parse second line (usage percentage)
    lines = result.stdout.strip().splitlines()
    usage_str = lines[1].split()[0].replace("%", "")
    usage = int(usage_str)
    
    if usage >= threshold_percent:
        print(f"[ALERT] Root filesystem at {usage}% capacity!")
        return 1
    
    print(f"[OK] Root filesystem nominal at {usage}%.")
    return 0

if __name__ == "__main__":
    sys.exit(check_disk_space())
PY

# Run it and show the exit code
python3 disk_check.py; echo "Exit status: $?"