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How UFO protected from DynamoDB outages

Context - The October 21 2025 AWS Outage 

I've just read a news article about Amazon Web Services (AWS) having a problem with their DynamoDB service which impacted a lot of their customers in the popular / vital US-EAST-1 region. This reminded me of another time that relying on DynamoDB caused an outage for one of the companies that I was working for when I lived in London, and how we went about preventing that from happening again.

"It's always DNS"

"Based on our investigation, the issue appears to be related to DNS resolution of the DynamoDB API endpoint in US-EAST-1." 

It's a cliché that outages on the Internet are often caused by some issue involving DNS, that happened to match up with the root cause this time around.

What's the UFO?

My team's core service was for capturing metadata about customers' usage of various components of the website. Because the service relied on DynamoDB for storing that information, we came up with a fallback service for the rare situations of DynamoDB being unavailable for any reason. At the time we were using short names for our services, typically based on the acronym of the service name - so I retro-fitted a service name to match with UFO as acronym, Usage Fallback Option.

How did it work?

The UFO service would write to an alternative data store that was independent of DynamoDB.

Clients of the normal usage service applied a circuit-breaker approach to interactions with the regular usage service, so the fallback service would automatically start to receive traffic if an outage occurred. 

Recovery scripts were available for either re-feeding the data into DynamoDB once it came back into service, or for progressing to the next phase of the data processing pipeline.

Should this approach be broadly applicable?

The short answer is "No."

In this particular situation we had a piece of functionality that was not visible to customers and was just an implementation detail of an asynchronous data procsesing pipeline.

On other projects I have worked on services that relied on DynamoDB as the primary data source involved in serving content on a website, so there was no similar fallback mechanism available there. Caches could have hidden some of the outage, but they were not intended to keep the site up.

It made sense to invest in the fallback service for usage as usage data acted as the transaction measurement of value being delivered when it came to contract negotiations with customers.

As the most recent outage only impacted a single region, I expect that the team would have been able to switch traffic to 0% in the impacted region. This would have been possible due to the regions being structures to be fully independent.

Addendum

Blast radius

From a brief skim-read of the AWS status page it is apparent that EC2 launching had a dependency on DynamoDB, I take that to imply that the UFO service would not have been able to scale up to pick up the full load of usage events.

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Location: Christchurch, New Zealand

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