Consider the time the renewal job took when rescheduling it

With throttling, renewal jobs can take a significant time to complete (e.g. when a bunch of domains are renewing around the same time). To make sure we can spread out the renewal as evenly as possible throughout the period, and to ensure the renewal checks on different workers stay in sync, consider the duration of the actual job execution when re-scheduling the check.

Author: gohai

lib/resty/auto-ssl/jobs/renewal.lua

@@ -254,12 +254,14 @@ end
 local function renew(premature, auto_ssl_instance)
   if premature then return end
 
+  local start = ngx.now()
   local renew_ok, renew_err = pcall(do_renew, auto_ssl_instance)
   if not renew_ok then
     ngx.log(ngx.ERR, "auto-ssl: failed to run do_renew cycle: ", renew_err)
   end
 
-  local timer_ok, timer_err = ngx.timer.at(auto_ssl_instance:get("renew_check_interval"), renew, auto_ssl_instance)
+  local delay = math.max(0, auto_ssl_instance:get("renew_check_interval") - (ngx.now() - start))
+  local timer_ok, timer_err = ngx.timer.at(delay, renew, auto_ssl_instance)
   if not timer_ok then
     if timer_err ~= "process exiting" then
       ngx.log(ngx.ERR, "auto-ssl: failed to create timer: ", timer_err)