In libpcp/src/access.c, DNS resolution for ACL entries is done
once, at __pmAccAddHost() time (generally the startup time of
the daemon). This ignore the possibility of DNS entries
changing. Given that there appears to be no posix resolver API
that lets apps know the TTL of DNS information they supply, the
app can really only use the the DNS data instantaneously.
So it seems to me that we would need to do the ACL name->address
resolution at __pmAccAddClient time (whenever clients connect).
Perhaps we can add a little cache-TTL of our own, if the libc
resolvers turn out measurably too slow.
Related, getmyhostid() in libpcp/src/access.c shouldn't
imagine that there is a single "real IP address" for the host,
nor that it is unchanging.