UltraDNS Pool Types Overview

UltraDNS pools group multiple DNS records under a single hostname so responses can be controlled by the selected pool type.

Pool behavior depends on the pool configuration so depending on the pool type, UltraDNS can return records by order, random selection, health state, failover configuration, weight, geography, source IP, autonomous system number, or geographic proximity.

Resource Distribution Pools

A Resource Distribution pool groups A or AAAA records and controls how those records are returned in DNS responses.

• Resource Distribution pools support Round Robin, Fixed, and Random serving methods.
• Round Robin rotates records in priority order.
• Fixed returns records in the configured order.
• Random returns records in a random order.
• Resource Distribution pools do not provide probing or failover behavior.

Simple Monitor / Failover Pools

A Simple Monitor / Failover pool provides basic monitoring, notification, and optional failover for a single primary record.

• The configured HTTP or HTTPS probe monitors the primary record from four geographic regions.
• If the primary record is determined to be unavailable based on the configured probe sensitivity, UltraDNS can serve the failover record.
• The failover record is not probed.
• Simple Monitoring can be used without a failover record when only monitoring and notification are required.

Simple Load Balancing Pools

A Simple Load Balancing pool provides basic load balancing across a small set of primary records with an optional backup record.

• Simple Load Balancing supports up to five primary A or AAAA records.
• The pool uses an HTTP or HTTPS monitor to check the primary records.
• If the primary records are unavailable, UltraDNS can serve the configured All Fail record.
• The All Fail record is not probed.
• Supported response methods include Round Robin, Random, and Priority Hunt.

SiteBacker Pools

A SiteBacker pool provides monitored failover and availability management across multiple records.

• SiteBacker pools can contain A, AAAA, or CNAME records.
• SiteBacker can use pool-level probes or record-level probes.
• Failover behavior is controlled by record state, probe state, probe threshold, priority, Max Active Records, Max Served Records, backup method, and All Fail configuration.
• Records can be returned using Round Robin, Fixed, or Random response methods.
• SiteBacker pools cannot contain both A and AAAA records. Separate pools are required for each address family.
• SiteBacker supports sub-pools when another SiteBacker or Traffic Controller pool is added as a pool record.

Traffic Controller Pools

A Traffic Controller pool extends SiteBacker behavior with weighted traffic distribution for global server load balancing.

• Traffic Controller pools can contain A, AAAA, or CNAME records.
• Each Traffic Controller record has a weight value that helps determine the traffic load sent to that record.
• Traffic Controller can use probes to evaluate record health and adjust serving behavior.
• Traffic Controller supports probe specifications that can place records into warning, critical, or failed states.
• If a record enters a critical state, Traffic Controller can reduce that record's weight while continuing to serve it.
• Traffic Controller pools cannot contain both A and AAAA records. Separate pools are required for each address family.
• Traffic Controller supports sub-pools when another SiteBacker or Traffic Controller pool is added as a pool record.

Directional Pools

A Directional pool returns DNS responses based on the requester, the selected Directional method, and the configured Directional records.

Directional pools support two method types: Filtering and Steering.

• Filtering routes traffic based on defined rules and policies.
• Filtering record types include Geolocation, Source IP, ASN, and ASN + Geolocation.
• Steering, also called Geo Proximity routing, routes DNS queries to the resource that is geographically closest based on latitude and longitude coordinates.
• Directional pools can return A records, AAAA records, CNAME records, sub-pools, or No Response records, depending on the pool configuration.
• No Response records return No Error / No Response for the configured region, source IP group, ASN group, or matching policy.
• Directional pools on the zone apex cannot contain CNAME records.
• If a Directional pool uses both Geolocation and Source IP records, the Conflict Resolves To setting determines which match takes precedence.
• For Geolocation pools, EDNS Client Subnet may be used when supplied by the recursive resolver unless ECS is ignored at the pool level.

Sub-Pools

SiteBacker and Traffic Controller pools can be used as sub-pools within another SiteBacker or Traffic Controller pool.

• A sub-pool has its own records and probes.
• From the parent pool's perspective, a sub-pool is treated like a pool record.
• If the sub-pool is active, the active records within the sub-pool can be returned as part of the parent pool response.
• If the sub-pool hostname is outside the current zone, UltraDNS treats it as a CNAME and returns the hostname as the response.

Backup Methods for SiteBacker and Traffic Controller Pools

SiteBacker and Traffic Controller pools can use backup methods to determine how UltraDNS responds when all primary records fail health checks.

• Fail Closed stops serving primary records when all primary records fail and returns an empty DNS response.
• Backup Response serves the configured All Fail record when all primary records fail.
• Fail Open continues serving the original records even if all health checks fail.
• Backup Response requires a configured All Fail record.
• Fail Open is not available when an All Fail record is configured.

Important Notes

• Not all record types support pools. The Add Pool option is only available for compatible record types.
• Resource Distribution pools do not provide monitoring or failover behavior.
• Simple Monitor / Failover and Simple Load Balancing use HTTP or HTTPS monitoring.
• SiteBacker and Traffic Controller pools cannot mix A and AAAA records in the same pool.
• Probe behavior depends on the selected pool type, probe type, probe threshold, record state, regional probe results, and backup method.
• Pool behavior can differ significantly by pool type. Review the pool configuration before converting or changing pool types.