Re: [PATCH proxmox-backup] acme: partially fix #6372: scale certificate renewal checks by lifetime

["Shannon Sterz" <s.sterz@proxmox.com>]

On Tue Apr 21, 2026 at 4:46 PM CEST, Manuel Federanko wrote:
> Start renewing a certificate once 2/3 of its total lifetime have passed,
> instead of the hardcoded 30 days. This stays consistent with many
> certificates, which are valid for 90 days.
>
> The update service runs daily, impose a 3 day minimum remaining lifetime
> to still be able to handle transient failures for certificate renewals.
>
> Signed-off-by: Manuel Federanko <m.federanko@proxmox.com>
> Fixes: https://bugzilla.proxmox.com/show_bug.cgi?id=6372
> ---
>  src/api2/node/certificates.rs          | 21 +++++++++++++++++++--
>  src/bin/proxmox-daily-update.rs        |  3 ++-
>  src/bin/proxmox_backup_manager/acme.rs |  3 ++-
>  3 files changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/src/api2/node/certificates.rs b/src/api2/node/certificates.rs
> index a69f6511..6e7b3326 100644
> --- a/src/api2/node/certificates.rs
> +++ b/src/api2/node/certificates.rs
> @@ -306,16 +306,33 @@ pub fn new_acme_cert(force: bool, rpcenv: &mut dyn RpcEnvironment) -> Result<Str
>  /// parameter is set).
>  pub fn renew_acme_cert(force: bool, rpcenv: &mut dyn RpcEnvironment) -> Result<String, Error> {
>      if !cert_expires_soon()? && !force {
> -        bail!("Certificate does not expire within the next 30 days and 'force' is not set.")
> +        let lead = cert_renew_lead_time()? / (24 * 60 * 60);
> +        bail!("Certificate does not expire within the next {lead} days and 'force' is not set.")
>      }
>
>      spawn_certificate_worker("acme-renew-cert", force, rpcenv)
>  }
>
> +/// When to start checking for new certs.
> +pub fn cert_renew_lead_time() -> Result<i64, Error> {
> +    let cert = pem_to_cert_info(get_certificate_pem()?.as_bytes())?;
> +    if let (Some(notafter), Some(notbefore)) =
> +        (cert.not_after_unix().ok(), cert.not_before_unix().ok())

no need to convert between `Option` and `Result` here. simply do:

    if let (Ok(notafter), Ok(notbefore)) = (cert.not_after_unix(), cert.not_before_unix()) {

here :)

> +    {
> +        // gets usually checked every day by the daily-update service,
> +        // start checking at least 3 days before expiry
> +        let lifetime = notafter - notbefore;
> +        let lead = std::cmp::max(lifetime / 3, 3 * 24 * 60 * 60);

i talked to Fabian a bit and we came to the following consensus
regarding the 3 day cut-off here. this function should probably just
encode the lead time itself, not the 3 day cut off as that is an
artifact of how we refresh acme certificates in the daily-update task.
essentially the plan is to have this function return the lead time as
follows:

1. for short-lived certificates (< 10 days) the lead time should be half
   of the lifetime of the certificate [1].
2. for other certificates the lead time should be 1/3 of the
   certificates lifetime [2].

this is based on recommendations by let's encrypt [1,2]. for
ultra-short-lived certificates, however, the daily update service will
only have very limited chances to successfully renew the certificate,
since it will only run once a day. hence, the 3 day cut-off should be
moved to the daily update service. the service should check the validity
of the certificate with the 3 day cut-off in mind. it should then call
the acme renewal endpoint with the `force` parameter set to `true` to
by-pass the validity check based on the lead time outlined above. does
that make sense?

[1]: https://letsencrypt.org/docs/integration-guide/
[2]: https://letsencrypt.org/2025/12/02/from-90-to-45#action-required

> +        Ok(lead)
> +    } else {
> +        Ok(30 * 24 * 60 * 60)
> +    }

tiny nit: imo it might be a bit cleaner to do `return Ok(lead)` in the
if branch above, drop the else and return `Ok(30 * 24 * 60 * 60)` by
default.

> +}
> +
>  /// Check whether the current certificate expires within the next 30 days.
>  pub fn cert_expires_soon() -> Result<bool, Error> {
>      let cert = pem_to_cert_info(get_certificate_pem()?.as_bytes())?;
> -    cert.is_expired_after_epoch(proxmox_time::epoch_i64() + 30 * 24 * 60 * 60)
> +    cert.is_expired_after_epoch(proxmox_time::epoch_i64() + cert_renew_lead_time()?)
>          .map_err(|err| format_err!("Failed to check certificate expiration date: {}", err))
>  }
>
> diff --git a/src/bin/proxmox-daily-update.rs b/src/bin/proxmox-daily-update.rs
> index c4d68e30..e5e96eb9 100644
> --- a/src/bin/proxmox-daily-update.rs
> +++ b/src/bin/proxmox-daily-update.rs
> @@ -75,7 +75,8 @@ async fn check_acme_certificates(rpcenv: &mut dyn RpcEnvironment) -> Result<(),
>      }
>
>      if !api2::node::certificates::cert_expires_soon()? {
> -        log::info!("Certificate does not expire within the next 30 days, not renewing.");
> +        let lead = api2::node::certificates::cert_renew_lead_time()? / (24 * 60 * 60);
> +        log::info!("Certificate does not expire within the next {lead} days, not renewing.");
>          return Ok(());
>      }
>
> diff --git a/src/bin/proxmox_backup_manager/acme.rs b/src/bin/proxmox_backup_manager/acme.rs
> index 57431225..d1a2323f 100644
> --- a/src/bin/proxmox_backup_manager/acme.rs
> +++ b/src/bin/proxmox_backup_manager/acme.rs
> @@ -415,7 +415,8 @@ pub fn plugin_cli() -> CommandLineInterface {
>  async fn order_acme_cert(param: Value, rpcenv: &mut dyn RpcEnvironment) -> Result<(), Error> {
>      if !param["force"].as_bool().unwrap_or(false) && !api2::node::certificates::cert_expires_soon()?
>      {
> -        println!("Certificate does not expire within the next 30 days, not renewing.");
> +        let lead = api2::node::certificates::cert_renew_lead_time()? / (24 * 60 * 60);
> +        println!("Certificate does not expire within the next {lead} days, not renewing.");
>          return Ok(());
>      }
>