I have a shell script that I use to monitor loading times and response codes on my live server cluster. It runs a total of 250 iterations every 5 minutes, distributed across 10 servers and 6 sites. It uses curl with the -w flag to return pertinent information which is then parsed by my shell script:

curl -svw 'monitor_load_times %{time_total} %{http_code}' -b 'server=$server' -m 15 -o /dev/null $url 2>&1

This information is then parsed by a graphing script that can display a number of different responses. However, curl will occasionally return a response code of "000". When this happens, it seems to happen multiple times at once despite being distributed over many iterations:

What I'm trying to work out is if this is a client-side issue that's skewing my results or if it's actually indicative of a server-side problem affecting my entire cluster. Does 000 mean that the connection was dropped? Database entries corresponding to curl iterations with that response code return "0.000" for the time_total value. All of the search results I've found for curl returning a code of 000 are related to HTTPS being unsupported, but all of my test URLs are HTTP.

(The spike in 500 errors is a completely unrelated issue that affected my servers last night.)