Sales Tax Fault Tolerance

Update: Avalara restored service after 23 minutes.

One of the really hard, but really cool features we built into the RunSignup Sales Tax System was fault tolerance of unavailability of our tax rate vendor, Avalara.

Avalara is widely regarded as the best tax rate calculation system available, which is why we selected them. However, we knew that most systems do have some downtimes and we wanted to survive those periods.

Well, we are 3 days into our full implementation across all states (except Colorado – but that is a separate story) and we have our first full outage of Avalara. We had a couple of errors from them yesterday as well.

For customers, we still process registrations. We use our own sales tax tables that have been populated from Avalara and get cached as we do specific tax lookups by zipcode as a backup. This makes our calculations pretty accurate. And if there is a difference in the end, we absorb the under-calculations. We hold the actual tax reporting calculations in a queue and will process them correctly with Avalara when they return to service. This ensures all tax payments and reports to states are accurate.

We are just a few minutes into this outage in a slow time of year (December), in the evening (6PM East Coast), and we have already processed 43 sales tax transactions with our backup. As Stephen says, “At least this is a good test of our failover implementation.”

For other vendors who are implementing a sales tax system, we highly recommend designing a backup/failover strategy. As always, we are happy to share what we did and how we did it with other registration and nonprofit ticket providers. We are all in this together…

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