除了 DNS 的 TTL 外,還有瀏覽器本身的 cache time...

在看「Reviewing Fastly’s New Approach To Load Balancing In The Cloud」這篇的時候被提醒:

However, most browsers have implemented their own caching layer that can override the TTL specified by the server. In fact, some browsers cache for 5-10 minutes, which is an eternity when a region or data center fails and you need to route end users to a different location.

我印象中沒那麼長,但也記不起來多長,所以查了一下...

結果 IE 在「How Internet Explorer uses the cache for DNS host entries」直接說三十分鐘 XDDD 這篇文章是 2011 年更新的,所以至少到 IE9 都是對的?

Internet Explorer 4.x and later versions modify how DNS host entries are cached by decreasing the default time-out value to 30 minutes.

Firefox 的值可以從 Mozilla networking preferences 這邊對 network.dnsCacheExpiration 的說明看到是 60 秒。

Google Chrome 沒找到官方的說明...

不過這可以知道當你要換 IP address 時,如果可以讓新舊 IP 都提供服務的話,至少規劃半個小時會比較保險。如果有其他理由而沒辦法同時提供服務的話,至少公告步驟裡要有「重開瀏覽器」這塊。

而作業系統自己的 cache 又是另外要計算進去的事了...

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One Response to 除了 DNS 的 TTL 外,還有瀏覽器本身的 cache time...

  1. Chikei says:

    有點舊,不過 https://bugs.chromium.org/p/chromium/issues/detail?id=164026 "which honors TTL = max(60s, server_reported_ttl)"

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