Hi,
I’ve been using WPT to test a CloudFront implementation, and have noticed that despite the general timing measurements being faster for requests to Cloudfront vs the Origin, the Speed Index seems to be consistently lower for the Origin.
Can anyone shed some light on why this might be? This behaviour has repeated fairly consistently across 180 tests, from varied geographic locations.
This is a test against the Origin from Sydney:
http://www.webpagetest.org/result/141214_D2_KAQ/
This is a test against the CF implementation from Sydney:
http://www.webpagetest.org/result/141214_VK_KAS/
And here’s the comparison:
http://www.webpagetest.org/video/compare.php?tests=141214_VK_KAS,141214_D2_KAQ
Again for a test from Ireland:
Origin
http://www.webpagetest.org/result/141214_TQ_K9C/
CF
http://www.webpagetest.org/result/141214_WY_K9G/
Comparison
http://www.webpagetest.org/video/compare.php?tests=141214_WY_K9G,141214_TQ_K9C
The origin always seems to fare better with visual progress. Cloudfront is set to cache everything, so there shouldn’t be an additional RT to fetch from the origin for any requests (with the exception of 3rd party scripts), assuming a cache-hit (response headers indicate that CF is mostly delivering hits).
The origin server is in AWS US west coast, CF is US east coast.
If anyone can set me straight on this, I’d really appreciate it.