Ceph » Linux kernel client

CONFIG_CEPH_LIB_USE_DNS_RESOLVER is disabled by default. Did you build your own libceph module?

I think the userspace component (request-key -> key.dns_resolver in your case?) is responsible for setting the TTL. Try enabling the in-kernel dns resolver logging with "echo 1 >/sys/module/dns_resolver/parameters/debug".

There should be a way to inspect and invalidate the in-kernel cache with keyctl.

i use CoreOS Container Linux and indeed ceph module is compiled with dns resolver module.

the userspace component is key.dns_resolver as you guessed, and it seems to no support ttl for a or aaaa :(
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/keyutils.git/tree/key.dns_resolver.c

if this can be useful to someone else here the command i use to clear the kernel dns resolver cache:
sudo keyctl clear $((16#$(sudo cat /proc/keys | grep .dns_resolver | awk '{print $1;}')))

Thanks

Looks right... If you have three mons, you can specify three ips on the mount command line and avoid the in-kernel dns resolver.