The DNS Cache Gotcha

I just received a notification that Avalara, a NetSuite bundle that we use to calculate tax, is planning to make DNS changes on June 30th. I’m cringing!

Let me explain…

Not that long ago, our primary DNS server got a new IP Address. Networking 101 tells us, this is not a problem. Right? Any system (including NetSuite) relying on that IP can simply flush the DNS cache, and the system will do a fresh lookup and find the new IP. Super easy!

And just for the record, any system that doesn’t flush their DNS cache falls back to a parameter called the TTL (time to live). Our DNS provider, Network Solutions, sets our TTL at 48 hours.

When the IP address of our primary DNS server changed, our SuiteTalk app that communicates with APIs at our location (see diagram below) stopped working.

DNS Lookup

NetSuite cached an incorrect IP for our primary name server. Even though the IP of my web service remained unchanged, my user event scripts in NetSuite began failing. They could not locate my APIs.

I contacted NetSuite and told them they needed to flush their DNS cache. No response. This drug on long enough that I made the following prediction: “If they don’t flush their DNS cache in the next couple of hours, the TTL is going to expire and the problem will fix itself.”

Within 10 minutes of my saying that… the problem fixed itself. Our outage lasted exactly 48 hours. Yikes!

This brings me back to Avalara. They sent a letter stating that on June 30th, any customer that continues to connect to their web service using a static IP will experience a service interruption. To me, this implies that they are actually changing the IP of their web service. They are assuming that customers who use a URL to locate their web service will be fine. Based on my experience, I’d give that a 50/50 chance.

Avalara customers, brace for impact!

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