IP swapping is a technique used to maintain service availability during server migrations without requiring a change to dependent systems. It involves redirecting traffic to a new server while preserving the previously assigned IP address for applications and services that are hardcoded to use it. This is particularly useful in production environments where downtime and service disruption are unacceptable.

Problem Statement: Many applications, particularly those integrating with external APIs, databases, or mobile applications, are configured with static IP addresses. When a server needs to be replaced, simply changing the IP address is often impossible due to these hardcoded dependencies. Attempting a direct migration would lead to service outages and require extensive updates across numerous systems.

Scenario & Solution Overview:

The process of IP swapping typically involves configuring a network device (often a router or firewall) to forward traffic destined for the old server’s IP address to the new server. This redirection is often managed dynamically, minimizing the need for manual intervention. The core principle is to create a “virtual” IP address that routes through the new server without modifying any application configurations.

Key Components & Techniques (as highlighted in the example):

• Netplan Configuration: Netplan is a network configuration tool used on Ubuntu systems. It allows for flexible and dynamic network setup, which is crucial for IP swapping. Specific configurations will dictate the forwarding rules.
• Dynamic DNS (DDNS): While not explicitly mentioned in the provided text, DDNS is frequently used in conjunction with IP swapping. It allows the old IP address to resolve to a domain name, which can then be used to access the service through the new server.
• Traffic Redirection: The core mechanism involves configuring a router or firewall to redirect traffic from the old IP address to the new server’s IP address.
• Integration with APIs & Services: The solution relies on the flexibility of APIs and other services to dynamically update their connection strings or endpoints when the underlying IP address changes.

Example Setup (as presented):

• Server A: (Old) Ubuntu 20.04 with IP: 192.168.0.4
• Server B: (New) Ubuntu 20.04 with a dynamically assigned IP address (e.g., 192.168.0.5)

Benefits:

• Minimal Downtime: The primary benefit is the avoidance of service interruption during the migration process.
• Reduced Complexity: Simplifies the migration process by eliminating the need to update numerous applications.
• Operational Efficiency: Allows sysadmins and DevOps engineers to manage changes more effectively.

Related Concepts:

• Server Migration
• Network Redirection
• Dynamic DNS (DDNS)
• Netplan
• Firewall Configuration
• Routing