I’ve been reading up on the exact functionality of the zero-downtime-failover (ZDF) feature.
According to Preventing site downtime – Cloudflare Help Center there is a limitation that under certain circumstances the failover only retries once:
Though the meaining of this sentence is not really clear to me.
Does this mean that CF will only perform ZDF and only do it for one other origin if one of these three response codes is received from the origin server? If so this would seem strange as those response codes should only be used by proxies and not by applications.
Or does this mean that CF will perform ZDF on any Status 5xx, but only do it once if 521-523 is received from origin?
What’s the exact mechanic here? When will ZDF be performed and when will CF give up and serve an error page?
Also does ZDF update the “healthy”-state of an origin?