I changed my default DNS servers, rebuilt the network on a VPS, but
/etc/resolv.conf failed to change to updated DNS servers.
OnApp 5.x, 6.x
OnApp doesn't overwrite resolvers during rebuilding the network. The resolvers are only put in place when the virtual server is being built. For existing virtual servers, these changes are done manually.
Rebuild Network should configure the NIC properties inside the virtual server. Add the iptables rules to the compute resource for the virtual machine's NICs to set up bridging according to the networks configured in OnApp.