Hello ML-1722,
Thank you for posting your query here!
I understand that your question is regarding the scenarios in which DNS repointing might be involved, along with an explanation of other potential networking updates that Azure might undertake during a zone failure.
Zone Failover Scenarios:
· When an entire availability zone becomes unavailable (due to maintenance, hardware failure, or other issues), Azure initiates failover procedures.
· Failover ensures that your services remain accessible by redirecting traffic to healthy zones.
· DNS repointing is one of the steps taken during this process.
Specific Scenarios for DNS Repointing:
Zone Unavailability: If a zone fails, Azure updates DNS records to redirect traffic away from the affected zone.
Storage Account Access: For storage accounts using ZRS, DNS repointing ensures that clients can still access the storage account even if one zone is down.
Service Endpoints: DNS records are updated to point to the remaining available zones’ endpoints.
Application-Level Handling: Applications should handle retries and re-establish connections after DNS updates.
Other Networking Updates:
While DNS repointing is common, other networking updates may also occur during failover:
Routing Updates: Azure updates internal routing tables to route traffic away from the failed zone.
Load Balancer Configuration: If you’re using a load balancer, its configuration may be adjusted to distribute traffic across healthy zones.
Virtual Network Gateway Updates: For services like VPN gateways, Azure may reconfigure routes to avoid the failed zone.
Application Considerations:
Applications must be resilient to transient failures during DNS updates.
Implement retry logic for any operations affected by DNS changes.
Monitor DNS propagation and adjust TTL values to minimize caching.
Please note that apart from DNS repointing, Azure orchestrates multiple actions to maintain availability during zone failures.
Do let us know if you have any further queries. I’m happy to assist you further.
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