在「Understanding Round Robin DNS (hyperknot.com)」這邊看到的,原文在「Understanding Round Robin DNS」這邊。
作者猜測是測到 Cloudflare 的 bug?
I've been trying to understand what this behavior is, and I highly suspect it's a bug in their network.
看起來遇到的情況是:
- 當 CDN 的後端伺服器是多組 IP address 時,
- 有一組 IP address 的服務中斷,
在這樣的情境下,Cloudflare 不會自動切到其他伺服器上,這件事情讓 Cloudflare 的 CTO John Graham-Cumming 跑到 Hacker News 上面回應 (id=41956258),從他的句子看起來他也認為不太正常,但不確定發生什麼事情:
Hmm. I've asked the authoritative DNS team to explain what's happening here. I'll let HN know when I get an authoritative answer. It's been a few years since I looked at the code and a whole bunch of people keep changing it :-)
My suspicion is that this is to do with the fact that we want to keep affinity between the client IP and a backend server (which OP mentions in their blog). And the question is "do you break that affinity if the backend server goes down?" But I'll reply to my own comment when I know more.
然後剛剛看到看起來這個功能內部沒有放給 free tier,但現在放了 (id=41974044):
Update: change is rolling out to do zero downtime failover on free accounts.
看起來之前是放在付費版的功能裡,然後內部討論後決定放到 free tier?