Sysadmin Give a domain a different IP?

Adding additional IPs to a server involves 2 main tasks

1. Adding and registering additional IPs to system network configuration
2. Configuring Nginx to use those additional IPs

Additional IPs System Configuration

For CentOS to add additional IP address, you need to first be assigned additional IP addresses by your web host or order the additional IPs. For instance, OVH calls additional IPs failover IPs.

OVH has a guide for adding and registering the additional IPs for CentOS and other Linux distributions to the system outlined at Network IP Aliasing | OVH Docs.

There's a previous discussion for this with tips at Sysadmin - How to add a IPv4 Failover Range to CentOS 7? including scripting the format for each
/etc/sysconfig/network-scripts/ifcfg-eth0:X file you need to create.

Example for CentOS 6 & 7

Example IP range 192.168.2.2 to 192.168.2.10 in SSH or shell script define IPLIST variable listing all additional IP addresses in single space separated list and define i variable with starting value of 0. Then a for ip in $IPLIST loop incrementing i variable by 1 for each IP listed in IPLIST

Code (Text):

IPLIST="192.168.2.2 192.168.2.3 192.168.2.4 192.168.2.5 192.168.2.6 192.168.2.7 192.168.2.8 192.168.2.9 192.168.2.10"
i=0
for ip in $IPLIST; do
  i=$(($i+1))
echo -e "\n/etc/sysconfig/network-scripts/ifcfg-eth0:${i}"; echo "
DEVICE="eth0:$i"
BOOTPROTO=static
IPADDR="$ip"
NETMASK="255.255.255.255"
BROADCAST="xxx.xxx.xxx.xxx"
ONBOOT=yes";
echo -e "\nifup eth0:${i}";
done

Gives following display only output

Code (Text):

/etc/sysconfig/network-scripts/ifcfg-eth0:2

DEVICE=eth0:2
BOOTPROTO=static
IPADDR=192.168.2.2
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:2

/etc/sysconfig/network-scripts/ifcfg-eth0:3

DEVICE=eth0:3
BOOTPROTO=static
IPADDR=192.168.2.3
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:3

/etc/sysconfig/network-scripts/ifcfg-eth0:4

DEVICE=eth0:4
BOOTPROTO=static
IPADDR=192.168.2.4
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:4

/etc/sysconfig/network-scripts/ifcfg-eth0:5

DEVICE=eth0:5
BOOTPROTO=static
IPADDR=192.168.2.5
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:5

/etc/sysconfig/network-scripts/ifcfg-eth0:6

DEVICE=eth0:6
BOOTPROTO=static
IPADDR=192.168.2.6
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:6

/etc/sysconfig/network-scripts/ifcfg-eth0:7

DEVICE=eth0:7
BOOTPROTO=static
IPADDR=192.168.2.7
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:7

/etc/sysconfig/network-scripts/ifcfg-eth0:8

DEVICE=eth0:8
BOOTPROTO=static
IPADDR=192.168.2.8
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:8

/etc/sysconfig/network-scripts/ifcfg-eth0:9

DEVICE=eth0:9
BOOTPROTO=static
IPADDR=192.168.2.9
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:9

/etc/sysconfig/network-scripts/ifcfg-eth0:10

DEVICE=eth0:10
BOOTPROTO=static
IPADDR=192.168.2.10
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

ifup eth0:10

Where the first entry /etc/sysconfig/network-scripts/ifcfg-eth0:2 would contain

Code (Text):

DEVICE=eth0:2
BOOTPROTO=static
IPADDR=192.168.2.2
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

and command to start up the interface for initial first time for eth0:2 would be

Code (Text):

ifup eth0:2

Example for CentOS 7 Only

For CentOS 7 there's a 2nd method for adding additional IPs to your system Linux Basics: Assign Multiple IP Addresses To Single Network Interface Card On CentOS 7 | Unixmen. Instead of separate /etc/sysconfig/network-scripts/ifcfg-eth0:X files where X increments, you add additional IPs within the same /etc/sysconfig/network-scripts/ifcfg-eth0 existing file defined by variable IPADDRx where x increments from 1 to number of IP addresses you want to add. Your file might not be named eth0 as it depends on your CentOS 7 network device naming scheme which you can find out via command below to check which network device belongs to your existing public IP address for your server:

Code (Text):

ifconfig

So if you existing /etc/sysconfig/network-scripts/ifcfg-eth0 file contain

Code (Text):

DEVICE=eth0
BOOTPROTO=static
IPADDR=192.168.2.1
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

adding additional example IPs above would add these additional entries

Code (Text):

IPADDR1="192.168.2.2"
IPADDR2="192.168.2.3"
IPADDR3="192.168.2.4"
IPADDR4="192.168.2.5"
IPADDR5="192.168.2.6"
IPADDR6="192.168.2.7"
IPADDR7="192.168.2.8"
IPADDR8="192.168.2.9"
IPADDR9="192.168.2.10"

so /etc/sysconfig/network-scripts/ifcfg-eth0 file with additional IPs would contain

Code (Text):

DEVICE=eth0
BOOTPROTO=static
IPADDR0=192.168.2.1
IPADDR1="192.168.2.2"
IPADDR2="192.168.2.3"
IPADDR3="192.168.2.4"
IPADDR4="192.168.2.5"
IPADDR5="192.168.2.6"
IPADDR6="192.168.2.7"
IPADDR7="192.168.2.8"
IPADDR8="192.168.2.9"
IPADDR9="192.168.2.10"
NETMASK=255.255.255.255
BROADCAST=xxx.xxx.xxx.xxx
ONBOOT=yes

again you can script for this IPLIST variable defining space separated list of additional IP addresses in a for ip in $IPLIST loop with starting i=0 variable that increments by a value of 1 for each IPLIST entry

Code (Text):

IPLIST="192.168.2.2 192.168.2.3 192.168.2.4 192.168.2.5 192.168.2.6 192.168.2.7 192.168.2.8 192.168.2.9 192.168.2.10"
i=0
for ip in $IPLIST; do
  i=$(($i+1))
  echo "IPADDR${i}=\"$ip\""
done

changing existing IPADDR line from

Code (Text):

IPADDR=192.168.2.1

to

Code (Text):

IPADDR0=192.168.2.1

Then restart your networking service

Code (Text):

service network restart

check the additional IPs registered on your system via command

Code (Text):

ifconfig

Configuring Nginx Additional IP Usage

To configure Nginx additional IPs, you need to first do the above to add the additional IPs to the system's networking configuration and for the IPs to show up in ifconfig output and be pingable. Nginx can setup Vhosts to use either name based hosting (default) sharing the main IP address or IP based hosting where a Vhost uses a dedicated or different IP address for main IP address. This is controlled by Nginx listen directive How nginx processes a request

Centmin Mod 123.09beta01 and higher have native support to configure Nginx vhost creation routines to use a separate second IP from the main server IP address via persistent config file /etc/centminmod/custom_config.inc set variable called SECOND_IP discussed and added at Beta Branch - update nginx vhost generator routines support second IP

Support secondary dedicated IP configuration for centmin mod nginx vhost generator, so out of the box, new nginx vhosts generated will use the defined SECOND_IP=111.222.333.444 where the IP is a secondary IP addressed added to the server.

You define SECOND_IP variable is centmin mod persistent config file outlined at Upgrade Centmin Mod - CentminMod.com LEMP Nginx web stack for CentOS you manually create the file at /etc/centminmod/custom_config.inc and add SECOND_IP=yoursecondary_IPaddress variable to it which will be registered with nginx vhost generator routine so that any new nginx vhosts created via centmin.sh menu option 2 or /usr/bin/nv or centmin.sh menu option 22, will have pre-defined SECOND_IP ip address set in the nginx vhost's listen directive.

So in persistent config file you create or already created at /etc/centminmod/custom_config.inc set in it

Code (Text):

SECOND_IP=111.222.333.444

So at centmin.sh menu option 2, 22 or nv command runs to create a fresh new Nginx vhost instead of server{} context's listen directive being listed as

Code (Text):

listen 80;

with SECOND_IP set it will become

Code (Text):

listen 111.222.333.444:80;

for HTTPS on port 443

instead of

Code (Text):

listen 443;

with SECOND_IP set it will become

Code (Text):

listen 111.222.333.444:443;

where you defined SECOND_IP=111.222.333.444

Thus allowing you to use a different server IP for new nginx vhosts generated automatically.

Now if you want to use a different IP address from main server IP or the one defined in SECOND_IP variable, then right now you would need to manually edit your Nginx vhost config file's listen directive yourself defining the additional IP you added earlier and restart Nginx server afterwards

Code (Text):

service nginx restart

or centmin mod command shortcut

Code (Text):

ngxrestart

You can spin up a test VPS to try this without touching your live VPS