Tie Route Server anycast advertisements to application health

Source facts

Microsoft’s Route Server anycast guidance requires NVAs to stop advertising a route when the local application instance becomes unavailable. The intent is to avoid sending traffic to a failed instance. The same guidance warns that BGP convergence can delay failover, so route-based recovery must be assessed against the application’s recovery requirements. Microsoft Learn.

Applicability

Use this review for an approved anycast design with regional NVAs and Route Server. Identify the application health signal that controls each advertised prefix, the alternate destination and the owner of the routing policy.

DSE recommendation

DSE recommends writing a withdrawal criterion that reflects application readiness. Have the application and network teams agree what observation should remove the local route and what permits its return. Include recovery behavior and return-path requirements in the test plan. Avoid equating appliance uptime with permission to continue advertising a failed application’s address.

Verification

In a controlled rehearsal, make the local application unavailable while leaving the NVA running. Observe the health decision, route withdrawal, remote path change and application recovery timestamps. Restore the service and inspect route readvertisement. Record measured interruption and unresolved session behavior rather than promising immediate or lossless failover.

Official references

Microsoft Learn: Anycast routing with Azure Route Server.