Comment by tialaramex

A log monitor? Or specifically the crt.sh codebase?

Yes, the logs are public and I ran equivalent monitoring for a previous employer before the pandemic. You will need to consume records at the rate they're created to keep up, Let's Encrypt have stats you can look at, if you can cope with twice their typical daily throughput you'll be fine on average, but peaks will swamp you temporarily so design for that.

You can choose whether to store everything, or just stuff you consider interesting, and you can choose whether to care forever or only until expiry (so 398 days)

If you want everything (full certificates), indefinitely, that's a lot of data. Um, several terabytes per year maybe?