3 ms·

Doesn’t that mean the cert is already invalid by the time certbot notices, so you already have an outage? And if certbot is running daily then that outage could

Doesn’t that mean the cert is already invalid by the time certbot notices, so you already have an outage? And if certbot is running daily then that outage could be up to 24 hours.

mholt 5y ago
Not if the last valid OCSP response is stapled to the certificate. Of course, clients can ignore that and use their own revocation lists/logic, which sometimes get pushed faster than OCSP responses. (Or clients can just block any certificates/CAs they want to, really.)
patrakov 5y ago
Technically, yes. However, if the certificate is used with With HAproxy or any other solution that provides a stapled OCSP response from some kind of cache (e.g. as a file updated by cron), it is possible to avoid the outage completely by fetching the fresh OCSP response every day, and not updating the on-disk copy if it says "bad". This way, the old but still valid copy is served to customers while the system takes the necessary steps to renew the certificate.
schoen 5y ago
There was an idea we discussed of "intent to revoke", but it ended up looking like a quite a bit of work for a small benefit, so the situation is as mholt describes. :-) For this specific reason, Certbot is recommended to run twice per day, and that is the default behavior in OS Certbot packages as well as the more recent official snap package. Further to mholt's point, not all clients will enforce OCSP at all, while if you're using stapling, the client is being told about the last-valid OCSP response, so the outage would probably be a fairly small minority of clients in either case.
- kiwijamo 5y ago
  I know of at least one OS Certbot package where the check is only done weekly--FreeBSD. Would be interested to know if the twice-daily approach is the default in other OS packages.
  - schoen 5y ago
    Wow, thanks for pointing this out. Do you know who maintains this for FreeBSD, by any chance?

Doesn’t that mean the cert is already invalid by the time certbot notices, so you already have an outage? And if certbot is running daily then that outage could be up to 24 hours.

mholt 5y ago

Not if the last valid OCSP response is stapled to the certificate. Of course, clients can ignore that and use their own revocation lists/logic, which sometimes get pushed faster than OCSP responses. (Or clients can just block any certificates/CAs they want to, really.)

patrakov 5y ago

Technically, yes. However, if the certificate is used with With HAproxy or any other solution that provides a stapled OCSP response from some kind of cache (e.g. as a file updated by cron), it is possible to avoid the outage completely by fetching the fresh OCSP response every day, and not updating the on-disk copy if it says "bad". This way, the old but still valid copy is served to customers while the system takes the necessary steps to renew the certificate.

schoen 5y ago

There was an idea we discussed of "intent to revoke", but it ended up looking like a quite a bit of work for a small benefit, so the situation is as mholt describes. :-) For this specific reason, Certbot is recommended to run twice per day, and that is the default behavior in OS Certbot packages as well as the more recent official snap package. Further to mholt's point, not all clients will enforce OCSP at all, while if you're using stapling, the client is being told about the last-valid OCSP response, so the outage would probably be a fairly small minority of clients in either case.

kiwijamo 5y ago
I know of at least one OS Certbot package where the check is only done weekly--FreeBSD. Would be interested to know if the twice-daily approach is the default in other OS packages.
- schoen 5y ago
  Wow, thanks for pointing this out. Do you know who maintains this for FreeBSD, by any chance?