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Gaps in waterfall specifically in IE
10-27-2014, 04:17 AM
Post: #13
RE: Gaps in waterfall specifically in IE
I work with Sundeep, and we finally figured out what was wrong.

The AWS support team checked on their side and confirmed that everything worked well, but the way we did our tests for OCSP stapling was actually flawed.

The OCSP stapling happens at the CloudFront edge level so every node from an edge location needs to do it. The first request returns immediately a non-stapled answer and the node fires an OCSP request to our CA and then caches the answer which is then used for the subsequent requests hitting that edge node. (The nodes currently don't share these caches, but I filed a feature request so that they try to use a shared storage for that content, like they do for static content.)

During our test we only executed a relatively small number of requests, so we never hit the same edge node twice and that's why it appeared the stapling was broken. When testing you need to fire a few hundreds of requests until consistently getting stapled responses.

As for explaining the rest of the gap from our waterfall graph, we saw that it often happens that the CPU is maxed out while loading our app, for multiple reasons:
  • sometimes due to multiple SSL connections started at the same time, since they are quite heavy during the negotiation phase
  • while other gaps can be explained due to heavy CPU use during the parsing of Javascript and CSS content (our webapp code is around 400K when minified and compressed)
When these overlap, the gap can grow even up to a few seconds, and it's exacerbated if the testing machine is not powerful enough.
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RE: Gaps in waterfall specifically in IE - alien_ - 10-27-2014 04:17 AM

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