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The Complete NGINX on Ubuntu Series: Part 15 – High Availability and Clustering
Ubuntu High Availability Tutorial Web Server NGINX

The Complete NGINX on Ubuntu Series: Part 15 – High Availability and Clustering

Welcome to Part 15 of our comprehensive NGINX on Ubuntu series! We’ll implement high availability and clustering solutions to ensure zero-downtime operations, automatic failover, and fault-tolerant infrastructure.

High Availability Fundamentals

High Availability (HA) ensures continuous service operation through redundancy, automatic failover, and fault tolerance, minimizing downtime and maintaining service quality during failures.

graph TD
    A[Clients] --> B[Virtual IP - VIP]
    B --> C[Primary NGINX Node]
    B --> D[Secondary NGINX Node]
    
    C --> E[Shared Backend Pool]
    D --> E
    
    E --> F[Backend Server 1]
    E --> G[Backend Server 2]
    E --> H[Backend Server 3]
    
    I[HA Components] --> J[Keepalived]
    I --> K[Heartbeat Monitoring]
    I --> L[Automatic Failover]
    I --> M[Shared Configuration]
    I --> N[Health Checks]
    
    style B fill:#e1f5fe
    style C fill:#e8f5e8
    style D fill:#fff3e0
    style I fill:#e3f2fd

Keepalived Setup

# Install Keepalived on both NGINX nodes
sudo apt update
sudo apt install keepalived -y

# Enable IP forwarding
echo 'net.ipv4.ip_forward = 1' | sudo tee -a /etc/sysctl.conf
echo 'net.ipv4.ip_nonlocal_bind = 1' | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

# Check network interface
ip addr show

Primary Node Configuration

# Configure Keepalived on Primary Node
sudo nano /etc/keepalived/keepalived.conf
# Keepalived configuration for Primary Node
global_defs {
    router_id NGINX_PRIMARY
    script_user root
    enable_script_security
}

# NGINX health check script
vrrp_script nginx_check {
    script "/usr/local/bin/nginx-health-check.sh"
    interval 2
    timeout 3
    rise 2
    fall 3
    weight -10
}

# Virtual Router Redundancy Protocol instance
vrrp_instance NGINX_HA {
    state MASTER
    interface eth0  # Change to your interface
    virtual_router_id 100
    priority 110
    advert_int 1
    
    authentication {
        auth_type PASS
        auth_pass nginx_ha_2024
    }
    
    # Virtual IP addresses
    virtual_ipaddress {
        192.168.1.100/24  # Your VIP
    }
    
    # Track scripts
    track_script {
        nginx_check
    }
    
    # Notification scripts
    notify_master "/usr/local/bin/nginx-master-notify.sh"
    notify_backup "/usr/local/bin/nginx-backup-notify.sh"
    notify_fault "/usr/local/bin/nginx-fault-notify.sh"
}

Secondary Node Configuration

# Configure Keepalived on Secondary Node
sudo nano /etc/keepalived/keepalived.conf
# Keepalived configuration for Secondary Node
global_defs {
    router_id NGINX_SECONDARY
    script_user root
    enable_script_security
}

# NGINX health check script
vrrp_script nginx_check {
    script "/usr/local/bin/nginx-health-check.sh"
    interval 2
    timeout 3
    rise 2
    fall 3
    weight -10
}

# Virtual Router Redundancy Protocol instance
vrrp_instance NGINX_HA {
    state BACKUP
    interface eth0  # Change to your interface
    virtual_router_id 100
    priority 100  # Lower priority than primary
    advert_int 1
    
    authentication {
        auth_type PASS
        auth_pass nginx_ha_2024
    }
    
    # Virtual IP addresses (same as primary)
    virtual_ipaddress {
        192.168.1.100/24
    }
    
    # Track scripts
    track_script {
        nginx_check
    }
    
    # Notification scripts
    notify_master "/usr/local/bin/nginx-master-notify.sh"
    notify_backup "/usr/local/bin/nginx-backup-notify.sh"
    notify_fault "/usr/local/bin/nginx-fault-notify.sh"
}

Health Check Script

# Create NGINX health check script (same on both nodes)
sudo nano /usr/local/bin/nginx-health-check.sh
#!/bin/bash

# NGINX Health Check for Keepalived
LOG_FILE="/var/log/nginx/ha-health.log"

log_event() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1" >> "$LOG_FILE"
}

# Check if NGINX process is running
if ! pgrep nginx > /dev/null; then
    log_event "NGINX process not running"
    exit 1
fi

# Check if NGINX responds to HTTP requests
if ! curl -f -s --max-time 5 http://localhost/health > /dev/null 2>&1; then
    log_event "NGINX not responding to HTTP requests"
    exit 1
fi

# Check NGINX configuration
if ! nginx -t > /dev/null 2>&1; then
    log_event "NGINX configuration test failed"
    exit 1
fi

# Check if we can bind to the VIP (when master)
VIP="192.168.1.100"
if ip addr show | grep -q "$VIP"; then
    if ! curl -f -s --max-time 5 "http://$VIP/health" > /dev/null 2>&1; then
        log_event "Cannot serve content on VIP $VIP"
        exit 1
    fi
fi

# Check system load
LOAD=$(uptime | awk -F'load average:' '{print $2}' | awk '{print $1}' | sed 's/,//')
if (( $(echo "$LOAD > 10.0" | bc -l) )); then
    log_event "System load too high: $LOAD"
    exit 1
fi

log_event "Health check passed"
exit 0

# Make executable: sudo chmod +x /usr/local/bin/nginx-health-check.sh

Notification Scripts

# Create master notification script
sudo nano /usr/local/bin/nginx-master-notify.sh
#!/bin/bash

# NGINX Master Notification Script
HOSTNAME=$(hostname)
VIP="192.168.1.100"
LOG_FILE="/var/log/nginx/ha-events.log"

log_event() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1" | tee -a "$LOG_FILE"
}

log_event "MASTER: $HOSTNAME became MASTER for VIP $VIP"

# Ensure NGINX is running
if ! systemctl is-active --quiet nginx; then
    log_event "Starting NGINX service"
    systemctl start nginx
fi

# Send notification
SUBJECT="NGINX HA: $HOSTNAME is now MASTER"
MESSAGE="$HOSTNAME has become MASTER for VIP $VIP at $(date)"

log_event "Master transition completed successfully"

# Make executable: sudo chmod +x /usr/local/bin/nginx-master-notify.sh
# Create backup notification script
sudo nano /usr/local/bin/nginx-backup-notify.sh
#!/bin/bash

# NGINX Backup Notification Script
HOSTNAME=$(hostname)
VIP="192.168.1.100"
LOG_FILE="/var/log/nginx/ha-events.log"

log_event() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1" | tee -a "$LOG_FILE"
}

log_event "BACKUP: $HOSTNAME became BACKUP for VIP $VIP"

# Ensure NGINX is running for health checks
if ! systemctl is-active --quiet nginx; then
    log_event "Starting NGINX service for health checks"
    systemctl start nginx
fi

log_event "Backup transition completed"

# Make executable: sudo chmod +x /usr/local/bin/nginx-backup-notify.sh
# Create fault notification script
sudo nano /usr/local/bin/nginx-fault-notify.sh
#!/bin/bash

# NGINX Fault Notification Script
HOSTNAME=$(hostname)
VIP="192.168.1.100"
LOG_FILE="/var/log/nginx/ha-events.log"

log_event() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1" | tee -a "$LOG_FILE"
}

log_event "FAULT: $HOSTNAME entered FAULT state for VIP $VIP"

# Try to restart NGINX
log_event "Attempting to restart NGINX service"
systemctl restart nginx

if systemctl is-active --quiet nginx; then
    log_event "NGINX restart successful"
else
    log_event "NGINX restart failed"
fi

log_event "Fault notification sent"

# Make executable: sudo chmod +x /usr/local/bin/nginx-fault-notify.sh

Shared NGINX Configuration

# Create identical NGINX configuration on both nodes
sudo nano /etc/nginx/sites-available/ha-cluster.example.com
# High Availability NGINX Configuration
upstream backend_cluster {
    server 192.168.1.10:8080 max_fails=3 fail_timeout=30s;
    server 192.168.1.11:8080 max_fails=3 fail_timeout=30s;
    server 192.168.1.12:8080 max_fails=3 fail_timeout=30s;
    server 192.168.1.13:8080 backup;
    
    keepalive 32;
}

# Server listening on VIP
server {
    listen 192.168.1.100:80;  # VIP address
    listen 80;  # All interfaces
    server_name ha-cluster.example.com;
    
    # Health check endpoint for Keepalived
    location /health {
        access_log off;
        return 200 "OK\n";
        add_header Content-Type text/plain;
        add_header X-Server-Name $hostname always;
        add_header X-Server-IP $server_addr always;
    }
    
    # Main application
    location / {
        proxy_pass http://backend_cluster;
        
        # Standard proxy headers
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        
        # HA-specific headers
        proxy_set_header X-HA-Node $hostname;
        proxy_set_header X-HA-VIP $server_addr;
        
        # Failover settings
        proxy_next_upstream error timeout http_500 http_502 http_503 http_504;
        proxy_next_upstream_tries 3;
        proxy_next_upstream_timeout 30s;
        
        # Timeouts
        proxy_connect_timeout 5s;
        proxy_send_timeout 10s;
        proxy_read_timeout 10s;
        
        # Response headers
        add_header X-Served-By $hostname always;
        add_header X-Upstream-Server $upstream_addr always;
    }
    
    # Status endpoint
    location /nginx-status {
        stub_status on;
        access_log off;
        allow 127.0.0.1;
        allow 192.168.1.0/24;
        deny all;
        
        add_header X-Server-Name $hostname always;
    }
}

Configuration Synchronization

graph TD
    A[Config Management] --> B[Git Repository]
    A --> C[Rsync Sync]
    A --> D[Shared Storage]
    
    B --> E[Version Control
Change Tracking
Rollback]
    C --> F[Real-time Sync
Automated Deploy
Consistency]
    D --> G[NFS/GlusterFS
Central Storage
Shared Access]
    
    H[Sync Methods] --> I[Push-based]
    H --> J[Pull-based]
    H --> K[Event-driven]
    
    style A fill:#e1f5fe
    style H fill:#e8f5e8
    style E fill:#fff3e0
    style F fill:#e3f2fd
    style G fill:#e8f5e8

# Create configuration sync script
sudo nano /usr/local/bin/nginx-config-sync.sh
#!/bin/bash

# NGINX Configuration Sync Script
PRIMARY_NODE="192.168.1.101"
SECONDARY_NODE="192.168.1.102"
CONFIG_DIRS=(
    "/etc/nginx/sites-available"
    "/etc/nginx/sites-enabled"
    "/etc/nginx/snippets"
)

sync_configs() {
    local source_node="$1"
    local target_node="$2"
    
    echo "Syncing configs from $source_node to $target_node"
    
    for config_dir in "${CONFIG_DIRS[@]}"; do
        rsync -avz --delete \
            "$config_dir/" \
            "root@$target_node:$config_dir/" \
            --exclude="*.tmp"
        
        if [ $? -eq 0 ]; then
            echo "Successfully synced $config_dir"
        else
            echo "Failed to sync $config_dir"
            return 1
        fi
    done
    
    # Test config on target
    ssh "root@$target_node" "nginx -t"
    
    if [ $? -eq 0 ]; then
        ssh "root@$target_node" "systemctl reload nginx"
        echo "Config sync completed"
    else
        echo "Config test failed on $target_node"
        return 1
    fi
}

# Sync based on current node
CURRENT_IP=$(hostname -I | awk '{print $1}')

case "$CURRENT_IP" in
    "$PRIMARY_NODE")
        sync_configs "$PRIMARY_NODE" "$SECONDARY_NODE"
        ;;
    "$SECONDARY_NODE")
        sync_configs "$SECONDARY_NODE" "$PRIMARY_NODE"
        ;;
    *)
        echo "Unknown node IP: $CURRENT_IP"
        exit 1
        ;;
esac

# Make executable: sudo chmod +x /usr/local/bin/nginx-config-sync.sh

HA Monitoring

# Create HA monitoring script
sudo nano /usr/local/bin/nginx-ha-monitor.sh
#!/bin/bash

# NGINX HA Monitor
VIP="192.168.1.100"

show_ha_status() {
    echo "=== NGINX High Availability Status ==="
    echo "Generated: $(date)"
    echo
    
    # VIP status
    echo "--- Virtual IP Status ---"
    if ip addr show | grep -q "$VIP"; then
        echo "✅ This node ($(hostname)) has VIP $VIP"
        echo "Status: MASTER"
    else
        echo "⚪ This node ($(hostname)) does not have VIP $VIP"
        echo "Status: BACKUP"
    fi
    echo
    
    # Keepalived status
    echo "--- Keepalived Status ---"
    if systemctl is-active --quiet keepalived; then
        echo "✅ Keepalived is running"
    else
        echo "❌ Keepalived is not running"
    fi
    echo
    
    # NGINX status
    echo "--- NGINX Status ---"
    if systemctl is-active --quiet nginx; then
        echo "✅ NGINX is running"
        
        # Test VIP connectivity
        if curl -f -s --max-time 3 "http://$VIP/health" > /dev/null 2>&1; then
            echo "✅ VIP health check passed"
        else
            echo "❌ VIP health check failed"
        fi
    else
        echo "❌ NGINX is not running"
    fi
    echo
    
    # Recent events
    echo "--- Recent HA Events ---"
    tail -5 /var/log/nginx/ha-events.log 2>/dev/null || echo "No recent events"
}

force_failover() {
    echo "Forcing failover by stopping Keepalived..."
    systemctl stop keepalived
    echo "Keepalived stopped. Failover should occur within seconds."
}

case "${1:-status}" in
    status)
        show_ha_status
        ;;
    failover)
        force_failover
        ;;
    watch)
        while true; do
            clear
            show_ha_status
            echo "Press Ctrl+C to exit..."
            sleep 5
        done
        ;;
    *)
        echo "Usage: $0 {status|failover|watch}"
        ;;
esac

# Make executable: sudo chmod +x /usr/local/bin/nginx-ha-monitor.sh

Testing HA Setup

# Setup and testing commands

# 1. Enable sites on both nodes
sudo ln -s /etc/nginx/sites-available/ha-cluster.example.com /etc/nginx/sites-enabled/

# 2. Test config on both nodes
sudo nginx -t

# 3. Start services on both nodes
sudo systemctl enable nginx keepalived
sudo systemctl start nginx keepalived

# 4. Check HA status
/usr/local/bin/nginx-ha-monitor.sh status

# 5. Test VIP connectivity
ping 192.168.1.100
curl http://192.168.1.100/health

# 6. Test failover - on primary node:
sudo systemctl stop keepalived
# Check if VIP moves to secondary

# 7. Test service failover - on master:
sudo systemctl stop nginx
# Check Keepalived detects failure

# 8. Monitor events
tail -f /var/log/nginx/ha-events.log

# 9. Watch status
/usr/local/bin/nginx-ha-monitor.sh watch

# 10. Test config sync
/usr/local/bin/nginx-config-sync.sh

What’s Next?

Excellent! You’ve implemented a robust high availability NGINX cluster with automatic failover, health monitoring, and configuration synchronization. Your infrastructure now provides zero-downtime operations and fault tolerance.

Coming up in Part 16: NGINX Performance Tuning and Optimization

References

This is Part 15 of our 22-part NGINX series. Your server now has enterprise-grade high availability! Next, we’ll fine-tune performance. Questions? Share them in the comments!

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