If you want to enable DNS by setting up a /etc/resolv.conf file, add DNS to your hosts lines as shown below.
hosts: ldap dns [NOTFOUND=return] files
The recommended configuration is:
hosts: files dns
ipnodes: files dns
If per-user authentication is used, the sasl/GSSAPI and Kerberos mechanisms expect the dns naming service to be configured and enabled. See the chapters on DNS in this administration guide for further details.