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sslhttpstls1.2keep-alive

Multiple SSL/TLS handshakes despite Keep-Alive and Session Identifier/Ticket enabled

I have some trouble finding out why I'm experiencing several SSL/TLS handshakes on the same page (for several resources on the same page, i.e. multiple HTTP requests), when both Keep-Alive and Session Identifiers/Tickets are active on the website/server.

I've recently activated TLS (https) on my website and therefore I wanted to check what impact this had on the speed/load performance of the site. When going through the waterfall diagram from both various speed tests on the internet (e.g. tools.pingdom.com and webpagetest.org) and Chrome Developer Tools, i see multiple SSL handshakes/negotiations on the same page, on different content. You can see an image of this here:

enter image description here

As can be seen, there are multiple SSL negotiations on different http requests within the same domaian. I'm wondering about this, as both Keep-Alive and Session identifiers & -tickets are active (checked via multiple tests such as the ones from webpagetest.org and ssllabs.com/ssltest/). Please do also note that I dont have access to the server (apache) configurations as I'm on a shared host.

Is what I'm experiencing possibly:

  • due to the server configuration limiting some amount of connections?
  • a misconfiguration of some sort?
  • something entirely else?
  • Me that have misunderstood something?

Please note that I'm a complete rookie in this field, but I've tried to find as much information regarding this topic, but sadly not an answer.

In case you would like to test something for yourself, the website is https://www.aktie-skat.dk

Solution

  • It is normal for a browser to establish multiple parallel connections to the same site since each connection can only request and load a single resource at a time. Even with HTTP keep-alive these resources do not get loaded in parallel over a single HTTP/1.x connection but only one after the other. This is only different with HTTP/2. Apart from that some requests might result in an Connection: close from server which requires the client to use a different connection for the next requests.

    In detail: The first two handshakes start at 0.362s and 0.333s and take each about 100ms. These are full handshakes. All the other TLS handshakes are way shorter (about 50ms) and are thus abbreviated handshakes using session resume. The second TCP/TLS connection could not use session resume yet since the TLS handshake for the first connection was not done yet and thus no session was available for resume.