DNS, Hostname, Alias

Q: When there are multiple NICs, how to generate /etc/hosts records?

When there are multiple NICs, and you want to use confignetwork to configure these NICs, suggest to use hosts table to configure the installation NIC (installnic) and to use nics table to configure secondary NICs. Refer to the following example to generate /etc/hosts records.

Best practice example:

  • There are 2 networks in different domains: mgtnetwork and pubnetwork

  • mgtnetwork is xCAT management network

  • There are 2 adapters in system node1: eth0 and eth1

  • Add installnic eth0 10.5.106.101 record in /etc/hosts, its alias is mgtnic

  • hostnames node1-pub and node1.public.com are for nic eth1, IP is 192.168.30.101

Steps:

  1. Add networks entry in networks table:

    chdef -t network mgtnetwork net=10.0.0.0 mask=255.0.0.0 domain=cluster.com
chdef -t network pubnetwork net=192.168.30.0 mask=255.255.255.0 domain=public.com

  2. Create node1 with installnic IP 10.5.106.101, its alias is mgtnic:

    chdef node1 ip=10.5.106.101 hostnames=mgtnic groups=all

  3. Configure eth1 in nics table:

    chdef node1 nicips.eth1=192.168.30.101 nichostnamesuffixes.eth1=-pub nicaliases.eth1=node1.public.com nictypes.eth1=Ethernet nicnetworks.eth1=pubnetwork

  4. Check node1 definition:

    lsdef node1
    Object name: node1
     groups=all
     ip=10.5.106.101
     hostnames=mgtnic
     nicaliases.eth1=node1.public.com
     nichostnamesuffixes.eth1=-pub
     nicips.eth1=192.168.30.101
     nicnetworks.eth1=pubnetwork
     nictypes.eth1=Ethernet
     postbootscripts=otherpkgs
     postscripts=syslog,remoteshell,syncfiles

  5. Execute makehosts -n to generate /etc/hosts records:

    makehosts -n

  6. Check results in /etc/hosts:

    10.5.106.101 node1 node1.cluster.com mgtnic
192.168.30.101 node1-pub node1.public.com

  7. Edit /etc/resolv.conf, xCAT management node IP like 10.5.106.2 is nameserver:

    search cluster.com public.com
nameserver 10.5.106.2

  8. Execute makedns -n to configure DNS

Q: How to configure aliases?

There are 3 methods to configure aliases:

  1. Use hostnames in hosts table to configure aliases for the installnic.

  2. If you want to use script confignetwork to configure secondary NICs, suggest to use aliases in nics table to configure aliases. Refer to Configure Aliases

  3. If you want to generate aliases records in /etc/hosts for secondary NICs and you don’t want to use the script confignetwork to configure these NICs, suggest to use otherinterfaces in hosts table to configure aliases. Refer to following example:

    • If you want to add node1-hd 20.1.1.1 in hosts table, and don’t use confignetwork to configure it, you can add otherinterfaces like this:

      chdef node1 otherinterfaces="node1-hd:20.1.1.1"

    • After executing makehosts -n, you can get records in /etc/hosts like following:

      20.1.1.1 node1-hd

Note: If suffixes or aliases for the same IP are configured in both hosts table and nics table, will cause conflicts. makehosts will use values from nics table. The values from nics table will over-write that from hosts table to create /etc/hosts records.

Q: How to handle the same short hostname in different domains?

You can follow the best practice example.

Best practice example:

  • There are 2 networks in different domains: mgtnetwork and pubnetwork

  • mgtnetwork is xCAT management network

  • Generate 2 records with the same hostname in /etc/hosts, like:

    10.5.106.101 node1.cluster.com
192.168.20.101 node1.public.com

  • Nameserver is xCAT management node IP

Steps:

  1. Add networks entry in networks table:

    chdef -t network mgtnetwork net=10.0.0.0 mask=255.0.0.0 domain=cluster.com
chdef -t network pubnetwork net=192.168.30.0 mask=255.255.255.0 domain=public.com

  2. Create node1 with ip=10.5.106.101, xCAT can manage and install this node:

    chdef node1 ip=10.5.106.101 groups=all

  3. Create node1-pub with ip=192.168.30.101, this node is only used to generate /etc/hosts records for public network, can use _unmanaged group name to label it:

    chdef node1-pub ip=192.168.30.101 hostnames=node1.public.com groups=_unmanaged

  4. Execute makehosts -n to generate /etc/hosts records:

    makehosts -n

  5. Check results in /etc/hosts:

    10.5.106.101 node1 node1.cluster.com
192.168.30.101 node1-pub node1.public.com

  6. Edit /etc/resolv.conf, for example, xCAT management node IP is 10.5.106.2 :

    search cluster.com public.com
nameserver 10.5.106.2

  7. Execute makedns -n to configure DNS

Q: When to use hosts table and nics table?

hosts table is used to store IP addresses and hostnames of nodes. makehosts use these data to create /etc/hosts records. nics table is used to stores secondary NICs details. Some scripts like confignetwork use data from nics table to configure secondary NICs. makehosts also use these data to create /etc/hosts records for each NIC.