The Trust IV blog is built with Drupal CMS and hosted on an Ubuntu / Apache platform. We also use SOLR for indexing and search. Under normal circumstances our blog is reasonably responsive, but yesterday our site developed an embarrassing problem. (Well one that's potentially embarrassing for a company for whom web performance is so important.)
The video below demonstrates the effect of a back-end component timing out (in our case the SOLR timeout was set to 30 seconds). The normal page response time for our site is around 3 seconds (as shown on the left) for a user on a typical broadband connection.
As you can see from our WebPagetest waterfall chart, the "time to first byte" was 30 seconds. This delay almost exactly matches the timeout value for requests sent from the Apache webserver to SOLR. Basically our webserver was waiting until it had "no response" from SOLR before serving up a page. Further investigation identified a firewall change (which prevented the webserver from communicating with the index and search engine) which resulted in this timeout and the associated delay. I'm pleased to report that things are back "up and running" normally now.