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I'm running an image-heavy website hosted on Windows Azure. Back-end performance is great but response times for image thumbnails, which make the bulk of page sizes, are quite volatile. I'm using the Azure CDN for serving all images but their response times vary by orders of magnitude and I haven't found any pattern in the fast (~150 milliseconds) vs slow (3-4 seconds) requests yet. This also doesn't seem to be a local phenomenon since I've tested the load times from different locations/continents. My conclusion so far is that the Azure CDN is simply not that good after all and I started looking for other ways to improve the load times of static assets.

Now that the context is clear, here is my actual question: does anyone have experience with services like Cloudflare and Incapsula for improving the performance of websites hosted on cloud infrastructure like Windows Azure? These services promise reduced server load among other things, but I'm more interested if they are actually effective in reducing response times for static files, as well as any negative impact on dynamic page content. I'd greatly appreciate any answers based on practical experience and/or advice for alternative solutions.

UPDATE: Here are the response headers for one of the images on the CDN:

HTTP/1.1 200 OK
Cache-Control: public, max-age:31536000
Content-Length: 4245
Content-Type: image/jpeg
Last-Modified: Sat, 21 Jan 2012 12:14:33 GMT
ETag: 0x8CEA64D5EC55FB6
Server: Windows-Azure-Blob/1.0 Microsoft-HTTPAPI/2.0
x-ms-request-id: d7a1ef38-6c99-4b38-a9f5-987419df5d24
x-ms-version: 2009-09-19
x-ms-lease-status: unlocked
x-ms-blob-type: BlockBlob
Date: Sun, 05 Feb 2012 12:56:12 GMT
Connection: keep-alive
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2 回答 2

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Incapsula 有两种缓存模式： 1) Basic - 此模式根据 http 标头中的指令缓存静态内容（与浏览器或商业缓存代理的行为方式相同）。这通常提供 30%-50% 的改进 2) 高级 - 此模式还缓存未在 http 标头中指定的静态内容和动态内容，方法是使用高级学习功能来确定哪些内容可缓存以及何时使缓存过期。这些方法经过优化，可以在最大缓存和提供新鲜/最新内容之间取得适当的平衡。此模式通常会增加 20%-30% 的额外改进。

于 2012-02-05T07:40:13.973 回答
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“这些服务承诺减少服务器负载等，但我更感兴趣的是它们是否真的有效减少静态文件的响应时间，以及对动态页面内容的任何负面影响。我非常感谢任何基于以下内容的答案实践经验和/或替代解决方案的建议。”

我们实际上不会影响您的动态内容，所以一切都应该很好去那里。

我们缓存静态内容。大多数用户看到整体性能提高了大约 50-60%，因此您绝对应该看到服务器上的静态资源的改进。

于 2012-02-04T16:19:50.270 回答