Re: DNS cache?

[Martin Pala]

Yet one hint - even if you use DNS round-robbin, it could be better to 
monitor both physical addresses/hostnames then virtual/multihost name.

This is because clients are directed randomly to one of your servers. In 
the case that one of them fails, ca. half of the requests will fail as 
well (unless you have dynamic DNS updates) - when you monitor both hosts 
directly, you will know the error as soon as possible. When you monitor 
loadballanced hostname, the error report can be delayed until you get 
failed node address from DNS.

In any case, it is useful to know that particular machine failed and 
that fix is needed, to solve temporary single point of failure.

Martin

Jonathan Trott wrote:
> I am monitoring a remote web cluster using monit. The cluster is connected 
> using multiple ADSL connections and the load is distributed using round 
> robin DNS with a TTL of 0. The problem is that when I test http using the 
> DNS name in monit, it appears to cache the DNS response the first time it 
> starts up and doesn't refresh the record. This means that if the link that 
> monit has cached the IP address of goes down, monit returns an alert even 
> though the other connections are fine and the website is still reachable.
> Can we get monit to follow the TTL of DNS records and lookup the record 
> again when that TTL has expired? This would also be useful for testing 
> servers/services hosted on dynamic DNS for instance.
> Thanks,
> JT
>
>
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