GSLB Vserver is not responding with GSLB Service IP or sending the empty DNS response despite the GSLB service is up.

In the below snippets, We could see that the GSLB Vserver is configured with 4 GSLB Services and Spillover Method is configured as HEALTH and Spillover threshold as 70%.

Only 2 out of 4 GSLB Services are Active. Thus Spillover Health Threshold has fallen to 50% and  the GSLB Vserver is not responding with GSLB Service IP despite the other 2 GSLB Services are UP.

NOTE: If "Empty Down Response" is enabled under GSLB Vserver, Then it will respond to DNS request with empty DNS response when the GSLB Server is Down or When the aforementioned Spilllover condition is met.

Configuration Snippet:

add gslb vserver <GSLB Vserver Name> ANY -dnsRecordType A -lbMethod STATICPROXIMITY -backupLBMethod LEASTCONNECTION -netmask 255.255.255.255 -v6netmasklen 128 -tolerance 0 -persistenceType SOURCEIP -persistenceId 101 -persistMask 255.255.255.255 -v6persistmasklen 128 -timeout 5 -EDR ENABLED -ECS DISABLED -ecsAddrValidation DISABLED -MIR DISABLED -disablePrimaryOnDown DISABLED -dynamicWeight DISABLED -state ENABLED -considerEffectiveState NONE -soMethod HEALTH -soPersistence DISABLED -soPersistenceTimeOut 2 -soThreshold 70 -soBackupAction ACCEPT -appflowLog DISABLED -noDefaultBindings NO

Log Snippet:

> Show gslb vserver <GSLB Vserver Name>

<GSLB VServer NAME> - ANY State: UP (Inactive:Health too low/No Backup configured)

DNS Record Type: A
Last state change was at Wed Dec 2 07:58:11 2020
Time since last state change: 132 days, 03:37:52.630
Configured Method: STATICPROXIMITY
BackupMethod: LEASTCONNECTION
No. of Bound Services : 4 (Total) 2 (Active)
Persistence: SOURCEIP
Persistence Mask: 255.255.255.255 Persistence v6MaskLength: 128
Persistence Timeout: 5 min Persistence ID: 101
Disable Primary Vserver on Down: DISABLED Site Persistence: NONE

Empty Down Response: ENABLED
EDNS Client Subnet: DISABLED
EDNS Client Subnet Address Validation: DISABLED
Multi IP Response: DISABLED
Dynamic Weights: DISABLED
Cname Flag: DISABLED
Effective State Considered: NONE
Spillover Method: HEALTH Health Threshold (by weight): 70 % Health (by weight) : 50%
Spillover Backup Action: ACCEPT
 

Spillover threshold is not usually recommended in GSLB setup. Hence, Either remove the Spillover threshold or configure the Threshold value accordingly by ensuring the availability of the services at any given instant

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Problem Cause

Working as expected. GSLB Vserver is configured with Spillover Threshold and the Threshold has gone below the configured  threshold. Thus the GSLB Vserver did not respond with the ip address of exisiting GSLB Service which are in UP state.