DNS resolution issue with CURL on AdHoc VM

[dmorissette]

Some DNS resolution issues with programs using the CURL library have been reported on the AdHoc VM recently: CURL is unable to resolve any hostname. OTOH, dig on the same hostname does work:

dmorissette@adhoc:/tmp$ curl -v http://www.google.com/
* getaddrinfo(3) failed for www.google.com:80
* Couldn't resolve host 'www.google.com'
* Closing connection #0
curl: (6) Couldn't resolve host 'www.google.com'

dmorissette@adhoc:/tmp$ dig www.google.com
[...]
;; ANSWER SECTION:
www.google.com.		604759	IN	CNAME	www.l.google.com.
www.l.google.com.	259	IN	A	74.125.155.106
[...]

Based on a quick web search, it seems that this kind of problem is related to the "hosts" setting in the /etc/nsswitch.conf.

We currently have the following line in /etc/nsswitch.conf:

hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4

... and I verified that if I put "dns" before "mdns4_minimal" then CURL works fine:

hosts:          files dns mdns4_minimal [NOTFOUND=return] mdns4

I would also note that I checked two other VMs (projects and backup) and none of them has the mdsn4 stuff, only a simple

hosts:          files dns

... so it seems that someone intentionally changed this in the AdHoc VM since it was created.

Unfortunately I don't know enough about the nsswitch.conf and mdns4 to be sure that the proposed fix above won't have other bad side-effects. Hopefully whoever added the mdns4 stuff will see this ticket and can confirm that the change to put "dns" right after "files" would be fine.

[dmorissette]

I applied the proposed fix in /etc/nsswitch.conf on the AdHoc VM and included a comment referring to this ticket:

# 2010-10-18: Moved dns right after files, see SAC ticket #644
hosts:          files dns mdns4_minimal [NOTFOUND=return] mdns4

Closing ticket. Please re-open if this change caused some side-effects.

[martin]

I think we can firmly assume every appliation which does _not_ work with "files dns" to be broken (as long as the 'hosts' file is correct ;-)