[Dnsmasq-discuss] Dealing with a unstable/slow upstream DNS

Simon Kelley simon at thekelleys.org.uk
Fri Oct 4 11:32:54 BST 2013


On 04/10/13 08:56, Joachim Berdal Haga wrote:
> Hi,
>
> I have tried to use dnsmasq on a compute cluster where the DNS is
> occasionally very slow. I was hoping to avoid the administration of a large
> host file on every node. But I have not been able to mask the problems
> completely:
>
> 1) I can maintain /etc/hosts on the master node, but the worker nodes will
> still query, and wait for, for AAAA records. The problem is compounded by
> the negative-lookup TTL being rather short. Is it possible to instruct
> dnsmasq to not forward AAAA requests when the A record is deduced from
> /etc/hosts (or vice versa)?

No, but you're not the first person to ask for this feature. I've been 
hesitant to add it because it introduces a form of pollution into the 
DNS that will make deploying IPv6 more difficult.
>
> 2) For cached entries (not in /etc/hosts), there is still the occasional
> hang when the entry expires. Which, as mentioned, happens fairly frequently
> for negative lookups. Is it possible to instruct dnsmasq to refresh its
> cache while replying immediately with the already cached record? Either
> optimistically (when the entry will soon expire) or lazily (when the entry
> has just expired).
>

No again. I once saw a patch to dnsmasq that did this for a number of 
configured domains. You can't really do it for all domains, since it 
will make the cache grow without bound - one a domain is in you can't 
ever lose it again.


> I have looked hard at the documentation, and so I guess that the answer to
> these questions is no :-) But still worth asking. And maybe there are other
> ways to deal with it?
>

Cheers,

Simon.
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