Hello, I recently setup a PWS - it is a Ambient Weather WS-2902. I monitor the DNS traffic on my network, and noticed in the less then 24 hours DNS requests for rtupdate.wunderground.com has passed 60% of all DNS records on my network - so far at 18,936 hits.
Looking more into the issue, I noticed that rtupdate.wunderground.com has a DNS TTL of 60 seconds. I understand that part of the problem is likely Ambient Weather WS-2902 not doing its own DNS caching. However, with a 60 seconds TTL, it wouldn't matter much even if it were. 60 seconds is very short. Please increase your TTL to at least 300 seconds (5 minutes). Not only would this reduce the load on your own DNS servers, but it would also reduce the network load of people with a PWS by allowing ISP's or other DNS providers to maintain a cache of greater then 60 seconds. It would also reduce latency by allowing the DNS cache to be effective. Of course greater then 5 minutes would be even better, but I understand the desire to keep cache time low in case a DNS entry needs modification.
RackSpace has a very logical best practices for DNS TTL here: https://support.rackspace.com/how-to/about-ttl-best-practices/
They recommend using a TTL of 24 hours and then lowering it to 5 minutes the day before any infrastructure changes.
Google.com uses a TLL of 5 minutes. Facebook.com also has a TTL of 5 minutes. Microsoft.com uses a TTL of 1 hour - which I personally think is the best of both worlds between caching and the desire to quickly make changes. Interestingly enough, facebook's API endpoints (api.facebook.com and graph.facebook.com and graph.instagram.com) also use a TTL of 1 hour - which makes a lot of since. The primary domains will be used when a user types it in on a browser, but the API endpoints are almost constantly being hit in the background and so benefit the most when it comes to cached DNS records. I think this same logic would easily apply to rtupdate.wunderground.com - as you can tell its being hit very often.
Thank you for your time and consideration