I have looked at all historical reports at https://letsencrypt.status.io and the result is covered in a write-up at https://medium.com/enigma-shards.

I’d be keen to hear any feedback and happy to amend accordingly. What I came up with was:

99.9% uptime if only “total disruptions” are taken into account; and

98% if partial disruptions are included (this goes up to 98.8% for 2017 only)

What surprised me was that the 2-server configuration doesn’t really seem to help much, except for seamless updates. I mention a few things that may be worth to look at but overall, I think guys here can be proud of themselves.

Here’s a couple of charts to bring in some color.

A complete text is at https://medium.com/enigma-shards, enjoy

It’s not surprising that the total duration and the number of “partial downtime” incidents are larger than for complete disruptions — you can notice that the chart above goes one order higher, even though it again uses a logarithmic scale. As a result, the overall up-time here was at around 98% at the end of September 2017. If you wonder what it would look like if we skipped the big incident in May 2016, the final up-time would go up to 98.8% in 2017 only.