The OneFS SmartConnect DNS server is designed to respond to delegated queries from a site DNS server for SmartConnect zones defined on the cluster. For load-balancing to be effective, it is critically important that the site DNS servers do not cache the results.
On the cluster side, the SmartConnect time-to-live (TTL) is configurable. The default is zero and should not be changed for normal use cases. To configure the TTL for a SmartConnect pool, use the following command:
isi network pools modify <pool id> --sc-ttl=0
For load-balancing to operate optimally, it is also important that the site DNS honors the TTL returned by the OneFS SmartConnect DNS server. If the site DNS “clamps the TTL,” it is possible for the site DNS server to erroneously return the same cached value if multiple client requests are received within the same “clamp window.”
Windows Server DNS 2003, 2008, 2012, 2016, and 2019, clamp the minimum TTL to one second. If many client requests are expected within a one-second timeframe, consider a different DNS server.
Newer versions of BIND have introduced features that affect the SmartConnect ability to load balance. Depending on the BIND DNS version, consider the following information:
Note: In an event where these limits are engaged, multiple clients receive the same IP address, negating the SmartConnect ability to load balance connections. As a best practice, test these limits in a lab environment and understand how each of these features affects a specific workflow.