This is a reason to force reverse resolution of IPs if they do not appear in the dfs.allow. If the IP appear in dfs.allow, there's no reason to reverse-resolve it.
On Mon, Jul 29, 2013 at 4:48 PM, Daryn Sharp <da...@yahoo-inc.com> wrote: > One reason is the lists to accept or reject DN accepts hostnames. If dns > temporarily can't resolve an IP then an unauthorized DN might slip back > into the cluster, or a decommissioning node might go back into service. > > Daryn > > > On Jul 29, 2013, at 8:21 AM, 武泽胜 wrote: > > I have the same confusion, anyone who can reply to this will be very > appreciated. > > From: Elazar Leibovich <elaz...@gmail.com> > Reply-To: "user@hadoop.apache.org" <user@hadoop.apache.org> > Date: Thursday, July 25, 2013 3:51 AM > To: user <user@hadoop.apache.org> > Subject: Why Hadoop force using DNS? > > Looking at Hadoop source you can see that Hadoop relies on the fact > each node has resolvable name. > > For example, Hadoop 2 namenode reverse look the up of each node that > connects to it. Also, there's no way way to tell a database to advertise an > UP as it's address. Setting datanode.network.interface to, say, eth1, would > cause Hadoop to reverse lookup UPs on eth1 and advertise the result. > > Why is that? Using plain IPs is simple to set up, and I can't see a > reason not to support them? > > >
