The risk of downtime is almost zero. Published content is stored and served as flat files. The editor runs on an entirely separate system.
All your published Unless content is saved as flat files in AWS S3 and served through the CloudFront CDN. This setup makes sure the content is cached in 50+ edge locations worldwide. If one of the edge locations goes down, the network automatically selects the next best edge location to serve your content.
Since there are no servers or running software involved in serving your content, we estimate a minimum of 99.99% uptime. And that's a conservative guess.
For our in-line editor and the content optimization features, we built a serverless infrastructure based on AWS Lambda and DynamoDB. Lambda executes on a 'per-call' basis, so system-wide crashes are highly unlikely. And we're in good company - DynamoDb is also used by Amazon and Netflix, so Unless shares the responsibility of keeping it up and running with big players.