What are the implications of setting DNS TTL with FabricPool?

Applies to

StorageGRID 11.x.x and later
Data ONTAP 9.2 and later
All AFF Platforms
FabricPool

Answer

Affects of TTL with DNS RR Group

•     TTL weights the amount of time before the next DNS record is resolved
•     For Instance:
  •         TTL value of 4 hours
  •         Host1 handles all IO for 4 hours straight
  •         After 4 hours Host2 handles all IO for the next 4 hours

DNS TTL (Time to Live)

•     Applies to each DNS record
•     Dictates how long the DNS query is cached for the specified record 
•     Speeds up name resolution
•     Default Value: 12 hours or 24 hours
•     Value of 0 does not cache the query

DNS RR (Round Robin) Group

•     Consists of multiple DNS records
•     Alternates resolution of records one at a time

DNS RR in FabricPool with StorageGRID

•     DNS RR is used to create High Availability Gateway Nodes
•     Gateway nodes establish HTTP sessions to send S3 operations to the Storage Nodes
•     TTL values can cause a single Gateway Node to establish all sessions to serve IO
  •     Performance Penalties can be seen due to Single Host serving all IO

Additional Information

Choosing TTL values

StorageGRID HA Groups

• Introduced in StorageGRID 11.3.0 release
• Recommend HA groups starting with StorageGRID 11.3.0
• Uses Virtual IPs (VIPs) to associate to the Active Node
• Does not require DNS RR for HA
• Failover Monitoring triggers failover for the following reasons:
  •         Active Node on which the interface is configured goes down
  •         Active interface goes down
  •         Load Balancer service stops on Active Node
  •         HA service stops on Active Node