Replying to
@kpcyrd@chaos.social
@kpcyrd@chaos.social I think when there's a 1/3rd of the lifetime left is a good rule of thumb for when to start trying to renew. 30 days from expiry for a 90 day cert, 2 days out for a 6 day, etc.
ARI is defined in https://www.rfc-editor.org/rfc/rfc9773.html We have the guts implemented in instant-acme if you want a rust reference, but it's low level and a full fledged client needs to string together the pieces.