How can I use managed DNS providers to route traffic during failover events?

Managed DNS providers can help you steer users to a healthy site or service during failures by changing DNS answers automatically based on health checks and policy. Here’s the common pattern.

1) Use multiple endpoints

Set up two or more targets, such as:

• Primary data center / cloud region
• Secondary region / disaster recovery site
• Active-active clusters
• CDN / load balancer endpoints

2) Put DNS in front of them

Create DNS records for your application hostname, for example:

• app.example.com -> primary load balancer
• app.example.com -> secondary load balancer

Managed DNS providers typically support:

• Failover records: return the primary unless it is unhealthy
• Health checks: probe HTTP, TCP, HTTPS, or a specific path
• Weighted routing: send most traffic to primary, some to secondary
• Latency/geolocation routing: choose the closest healthy endpoint
• Geo failover: use regional backups if a region fails

3) Configure health checks

Tell the DNS provider what “healthy” means:

• HTTP GET /health
• Response code 200
• Optional content match like "ok"
• Retry thresholds and timeout settings

This allows DNS answers to change automatically when the primary stops responding.

4) Set failover policy

Typical setup:

• Primary answer if health check passes
• Secondary answer if primary fails
• Optional tertiary or “backup” target for additional resilience

Some providers also support “evaluate target health” for load balancers or aliases.

5) Tune TTL carefully

DNS failover is not instant because resolvers cache answers.

• Use a low TTL for failover-sensitive records, often 30–300 seconds
• Lower TTL = faster switchover, but more DNS queries
• Remember some clients and resolvers may ignore TTL or cache longer than expected

6) Make sure the app is ready for failover

DNS only moves new connections to the new endpoint. Ensure:

• Sessions are stateless or replicated
• Databases have replication/failover plans
• Certificates exist on all endpoints
• External dependencies are available in both sites
• The backup site can actually handle traffic

7) Test failover regularly

Simulate outages and verify:

• Health checks detect failure
• DNS records switch as expected
• Applications work after the switch
• Failback is controlled and doesn’t flap

8) Be aware of DNS limitations

DNS-based failover is useful, but not perfect:

• Existing clients may keep using cached results
• Browsers, ISPs, and mobile networks can cache aggressively
• It’s best for steering traffic, not for immediate real-time cutover

For very fast failover, combine DNS with:

• Global load balancers
• Anycast
• CDN failover
• Application-level retries and circuit breakers

Example architecture

1. app.example.com points to a managed DNS record
2. DNS provider checks https://primary.example.com/health
3. If healthy, return primary load balancer IP/CNAME
4. If unhealthy, return secondary region’s load balancer
5. TTL is set to 60 seconds
6. Monitoring and alerting notify operators

Popular managed DNS features to look for

• Health checks
• Primary/secondary failover
• Weighted records
• Geo/latency routing
• API automation
• Low TTL support
• Integration with cloud load balancers

If you want, I can also show you:

• a specific example using Route 53, Cloud DNS, Azure DNS, or Cloudflare, or
• a sample failover configuration and health-check setup.