A Beginner’s Guide to DNS Failover: Keeping Your Services Online 24/7

In today’s digital economy, availability is not a feature; it’s an expectation. When a server or application goes down, the consequences can be immediate and severe. Unplanned downtime halts operations, erodes customer trust, and inflicts significant financial damage on an organization.

For many businesses, these disruptions can cost an average of $6,000 per minute. DNS failover is designed to mitigate this risk, acting as an automated safeguard that routes traffic away from failing infrastructure, ensuring business continuity and keeping your domain online.

What is DNS Failover?

DNS failover is an automated process that maintains the availability of websites, applications, and services by redirecting user traffic from an unhealthy or unavailable server to a healthy standby server. It is a dynamic form of traffic management that operates at the level of the Domain Name System (DNS), the internet’s foundational directory service.

Imagine your primary web server is like the main entrance to your corporate headquarters. If that entrance is suddenly blocked due to an unforeseen issue, a DNS failover system acts like a security guard who immediately directs all incoming visitors to a secondary entrance without them even noticing the disruption.

How Does DNS Failover Work?

The mechanics of DNS failover rely on a coordinated system of monitoring, detection, and DNS record modification. This process is designed to be swift and automatic, removing the need for manual intervention during an outage. The key components of this system include:

1. Continuous Health Monitoring: The foundation of any DNS failover solution is a network of monitoring nodes. These nodes are strategically placed in different geographic locations around the globe and are configured to perform regular “health checks” on your primary servers. Checks can range from a simple ping (ICMP) to verify basic network connectivity, to more sophisticated probes like TCP port checks to ensure a specific service is listening, or HTTP/HTTPS requests that check for a specific response code to confirm an application is running correctly.
2. Failure Detection: The monitoring nodes execute these health checks at predefined intervals; every 30 seconds, for example. A failure is declared when a certain number of consecutive checks from multiple locations fail to receive a healthy response. This multi-location approach helps prevent false positives that could be caused by localized network issues between a single monitoring node and the server. Once the predefined failure threshold is met, the system triggers a failover event.
3. DNS Record Modification: Upon detecting a failure, the DNS failover service automatically modifies the DNS records for the affected domain. Specifically, it modifies the IP the A record (or AAAA record for IPv6) is pointing to. If an active-passive setup is used, it will replace the primary IP with the secondary IP. In an active-active setup, it simply removes the unhealthy IP from the rotation.
4. The Role of Time-To-Live (TTL): A critical setting in this process is the Time-To-Live (TTL) value of the DNS record. TTL tells recursive DNS servers around the world how long to cache a DNS response. For effective failover, a low TTL (like 60-300 seconds) is essential. A low TTL ensures that when the DNS record is updated, the change propagates quickly across the internet, directing traffic to the new, healthy server with minimal delay.
5. Failback: Once the primary server recovers and starts passing health checks again, the failover system can initiate a failback. This process reverses the DNS change, restoring the primary server’s IP address to the active pool and redirecting traffic back to it. Most systems allow for both automatic and manual failback to give administrators control over the restoration process.

What are the different types of DNS Failover?

DNS failover is not a one-size-fits-all solution. The optimal configuration depends on an organization’s specific requirements for availability, performance, and cost. There are two primary models for implementing DNS failover.

Active-Passive Failover

The Active-Passive model is one of the most common and straightforward failover strategies. In this configuration, you have a primary server (Active) that handles all incoming traffic under normal conditions and one or more secondary servers (Passive) that remain on standby.

The passive server is a replica of the active one, with identical data and applications, but it does not receive any live traffic. The DNS failover system continuously monitors the health of the active server. If the primary server fails, the system automatically updates the DNS records to redirect all traffic to the passive server, which then becomes active. This approach is cost-effective as the standby resources can sometimes be lower-spec or used for other non-critical tasks until they are needed. The main goal of this model is disaster recovery and ensuring business continuity with a clear backup resource.

Active-active failover

In an Active-Active configuration, two or more servers are simultaneously active and share the traffic load. This model is often used for both high availability and load balancing. DNS routing policies, such as round-robin or latency-based routing, distribute incoming requests across all healthy servers in the pool.

If one of the servers in the active-active pool fails its health checks, the DNS failover system simply removes its IP address from the DNS records. The remaining active servers seamlessly absorb the traffic that would have gone to the failed server. This model offers superior performance and resilience, as there is no delay in activating a standby server —the other servers are already running and handling requests. It provides built-in redundancy and can improve application response times for users by directing them to the geographically closest server.

What are the benefits of DNS failover?

Implementing a robust DNS failover strategy provides tangible benefits that directly impact an organization’s bottom line, reputation, and operational stability.

• Enhanced High Availability and Reliability: The primary benefit is a significant reduction in downtime. By automatically redirecting traffic during an outage, DNS failover ensures that your services remain accessible to users, directly contributing to higher uptime percentages and service level agreement (SLA) compliance.
• Business Continuity and Disaster Recovery: DNS failover is a critical component of any comprehensive business continuity or disaster recovery (BC/DR) plan. It enables organizations to survive server failures, data center outages, or even regional disasters with minimal disruption to services. This resilience is vital in an era where 87% of organizations have experienced DNS attacks, underscoring the need for rapid recovery mechanisms.
• Improved User Experience: For end-users, seamless failover means they are unaware that a problem even occurred. Preventing service interruptions and error pages protects the user experience, which is crucial for maintaining customer satisfaction and loyalty.
• Protection of Revenue and Brand Reputation: Every minute of downtime translates to lost revenue, decreased productivity, and potential damage to a company’s brand. DNS failover directly mitigates these financial and reputational risks by keeping revenue-generating applications online.
• Simplified Outage Response: Automating the failover process frees IT teams from scrambling to manually reroute traffic during a crisis. This allows them to focus on diagnosing and resolving the root cause of the failure rather than managing its immediate impact on users.

How to Configure DNS Failover?

Setting up DNS failover typically involves using a managed DNS provider that offers this feature. The specific steps vary by provider, but the general process follows a consistent framework:

1. Select a Capable DNS Provider: Choose a provider that offers advanced features like DNS failover, health checks, and a global monitoring network. Look for providers with a strong track record of reliability and a low-latency infrastructure.
2. Define Your Server Pools: Create a pool of IP addresses for your application. This will include your primary server and your secondary or backup servers. With DNSME, you can configure up to five IP addresses for each of your host names, for example.
3. Configure Health Checks: For each IP address in your pool, configure a health check. Define the type of check (HTTP, HTTPS, TCP, or Ping), the port to monitor, the expected response, the monitoring frequency , and the failure threshold.
4. Create a Failover Record: Create a DNS record and associate it with your server pool and health check configuration. Specify the failover logic. For example: “If the primary IP fails, replace it with the failover IP.”
5. Set a Low TTL: Ensure the TTL for your failover record is set to a low value, typically between 60 and 300 seconds. This is critical for ensuring that DNS resolvers worldwide quickly fetch the updated IP address after a failover event.
6. Test the Failover Process: The most critical step is to test your configuration. Simulate a failure on your primary server (e.g., by stopping the web service or blocking the port with a firewall) and verify that traffic is automatically redirected to the backup server within the expected timeframe. Also, test the failback process to ensure a smooth return to normal operations.

How Managed DNS Reduces Complexity

The above process may sound a bit daunting if you’re new to DNS failover, but managed DNS services simplify the process by offering an existing infrastructure for monitoring and DNS resolution. What should you look for in a managed DNS provider?

1. Global, redundant infrastructure & high uptime: If the DNS layer goes down, all your services that rely on that name resolution can vanish. Look for a provider whose DNS network is globally distributed so that DNS queries from all over the world are answered quickly and reliably.
2. Automated failover and health checks: DNS failover is only useful if the system detects your failure in time and redirects traffic swiftly.
3. Low TTL: To make failover effective, you’ll want low TTLs — like a two to four minute monitoring window — for the relevant DNS records so change propagates quickly.
4. Security features: One of the benefits of a managed DNS service is that providers often invest in the security of their infrastructure, ensuring better defenses than you might be able to provide on your own.

DNS Made Easy makes failover easy

Failover should be a standard process for all organizations.

DNS Made Easy’s failover service is a powerful yet simple tool that automatically updates DNS records, guaranteeing resource availability even when the primary endpoint fails. By understanding the technical aspects, key terminology, and implementation tips, you can leverage failover mechanisms to ensure uninterrupted service for your enterprise.

Ensure uninterrupted resource availability with DNSME’s failover service. Explore our comprehensive DNS failover solutions, backed by industry-leading reliability and expertise. If your organization does not have DNS failover enabled, one of our DNS experts would be more than happy to assist with a game plan for success with a customized demo.