I have experienced a strange situation in which squid repeatedly returns dns resolution error messages even though I can resolve the same names at the command line, and even fetch the same pages via wget. Running squid -k reconfigure fixes the problem immediately.
My first theory was that there is some sporadic network outage, but once its fixed squid retains the negative dns cache of failed requests. So I tried lowering the negative_dns_ttl setting down to a few seconds, but it didn't help. This problem is hard to diagnose because this server is in production and I can't afford cranking up the logs and wait until it happens again, and I also have to be quick to fix it instead when this situation happens instead of spending more time investigating the cause. I wrote a perl script that "tails" the access log to detect when this error condition happens and then automatically runs squid -k reconfigure and informs me via email. This script is useful to warn me about error conditions, even if they are unrelated to Squid, and I would like to retain it even if I can solve the root problem. But at the same time I would like to improve it by using the Cache Manager interface, or SNMP, and somehow get the number of failed requests and total requests served in the last x minutes. Is it possible to get this information in this way instead of reading the access log? So I would appreciate any help with both issues: 1. strange dns cache problem 2. improving my monitoring via Cache Manager or SNMP Thanks.
