Does anyone know what if any is the overhead when I specify hostnames instead of IP addresses for all nodes in a pool, with 2000 Load Balancers, each having 3 nodes in a Pool.
We'll hammer your DNS server quite hard when we start up, as we'll need to resolve these dns names to IPs. This will delay the startup time.
Once we've done that, we cache the results and refresh occasionally. Default is every 24 hours, but you can configure this on the Global Settings -> System Settings page.
Caching it for 24 hours? Tsk...
There is a field named TTL in the DNS reply which is authoritative for the amount of time you can cache this information.
Hi Edwin - good point.
Rather than resolving the DNS entries once and using the result in perpetuity, we explicity re-resolve every 24 hours (or whatever the Stingray admin configures). We generally use the OS functions to perform DNS resolution; these don't return TTL values but the OS cache (if there is one) or the local nameserver will respect the TTL to reduce the load on the nameserver and improve resolution performance.
The implication is that if the DNS admin configures a TTL of less that 24 hours, we'll round it up to 24 hours.
CORRECTION: the 24-hour re-resolution does not apply to dns names in pool configurations. We use a different system for those, and they are re-resolved every 30 seconds (by default). If you need to change that period, check out the expert key 'dns!checktime' as described in Configuration System Guide in the Stingray Product Documentation. Note that intermediate DNS resolvers may cache the result for 24 hours (or whatever your TTL may be) - it all depends on your configuration for your DNS entries and the resolution path that you define.