Setting up a Load-Balancing LVS (NAT) Cluster with Piranha

Linux Virtual Server (LVS) system offers a highly-available and scalable solution for production services using specialised routing and load-balancing techniques that can be configured through the Piranha configuration tool. 

Software

Software used in this article:

  1. CentOS 6.7
  2. Piranha 0.8.6
  3. Ipvsadm 1.26

LVS Cluster

A Linux LVS cluster consists of two basic groups: the LVS routers and the real servers. To prevent a single point of failure, each group will contain two member systems.

As per CentOS documentation, the active router serves two roles in the cluster:

  1. To balance the load on the real servers,
  2. To check the integrity of the services on each of the real servers.

The backup router’s job is to monitor the active router and assume its role in the event of failure.

LVS Components

Pulse: this is the controlling process which starts all other daemons related to LVS routers. At boot time, the daemon is started by the /etc/rc.d/init.d/pulse script. It then reads the configuration file /etc/sysconfig/ha/lvs.cf. On the active router, pulse starts the LVS daemon. On the backup router, pulse determines the health of the active router by executing a simple heartbeat at a user-configurable interval.

lvs: the lvs daemon runs on the active LVS router once called by pulse. It reads the configuration file /etc/sysconfig/ha/lvs.cf, calls the ipvsadm utility to build and maintain the IPVS routing table, and assigns a nanny process for each configured LVS service. If nanny reports a real server is down, lvs instructs the ipvsadm utility to remove the real server from the IPVS routing table.

ipvsadm: this service updates the IPVS routing table in the kernel.

nanny: the nanny monitoring daemon runs on the active LVS router. Through this daemon, the active router determines the health of each real server and, optionally, monitors its workload. A separate process runs for each service defined on each real server.

Piranha configuration tool: this is the Web-based tool for monitoring, configuring, and administering an LVS cluster. This is the default tool to maintain the /etc/sysconfig/ha/lvs.cf LVS cluster configuration file.

/etc/sysconfig/ha/lvs.cf: this is the LVS cluster configuration file. Directly or indirectly, all daemons get their configuration information from this file.

Networking and IP Addresses

Our networks are set up as follows:

  1. 10.8.8.0/24internal network with no access to the Internet, but with a local DHCP server,
  2. 10.10.1.1/24 – LAN with access to the Internet.

Hostnames and roles of the virtual machines we are going to use:

  1. lvs-01 – the active LVS router,
  2. lvs-02 – the backup LVS router,
  3. lvs-03/lvs-04 – real servers, both running a pre-configured Apache webserver with SSL.

See the schema below for more information.

LVS-01 and LVS-02 Nodes’ Network Configuration

Network configuration on the lvs-01 node:

[[email protected] ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=static
PEERDNS=no
USERCTL=no
IPADDR=10.10.1.31
NETMASK=255.255.255.0
GATEWAY=10.10.1.1
[[email protected] ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE=eth1
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=dhcp
PEERDNS=yes
USERCTL=no

Routing table on the lvs-01:

[[email protected] ~]# ip ro
10.10.1.0/24 dev eth0  proto kernel  scope link  src 10.10.1.31
10.8.8.0/24 dev eth1  proto kernel  scope link  src 10.8.8.31
169.254.0.0/16 dev eth0  scope link  metric 1002
169.254.0.0/16 dev eth1  scope link  metric 1003
default via 10.10.1.1 dev eth0

Network configuration on the lvs-02 node:

[[email protected] ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=static
PEERDNS=no
USERCTL=no
IPADDR=10.10.1.32
NETMASK=255.255.255.0
GATEWAY=10.10.1.1
[[email protected] ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE=eth1
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=dhcp
PEERDNS=yes
USERCTL=no

Routing table on the lvs-02:

[[email protected] ~]# ip ro
10.10.1.0/24 dev eth0  proto kernel  scope link  src 10.10.1.32
10.8.8.0/24 dev eth1  proto kernel  scope link  src 10.8.8.32
169.254.0.0/16 dev eth0  scope link  metric 1002
169.254.0.0/16 dev eth1  scope link  metric 1003
default via 10.10.1.1 dev eth0

LVS-03 and LVS-04 Real Servers Nodes’ Network Configuration

Network configuration on the lvs-03 node:

[[email protected] ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE=eth1
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=static
PEERDNS=no
USERCTL=no
IPADDR=10.8.8.33
NETMASK=255.255.255.0
GATEWAY=10.8.8.30

Routing table on the lvs-03:

[[email protected] ~]# ip ro
10.8.8.0/24 dev eth1  proto kernel  scope link  src 10.8.8.33
169.254.0.0/16 dev eth1  scope link  metric 1002
default via 10.8.8.30 dev eth1

Network configuration on the lvs-04 node:

[[email protected] ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE=eth1
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=static
PEERDNS=no
USERCTL=no
IPADDR=10.8.8.34
NETMASK=255.255.255.0
GATEWAY=10.8.8.30

Routing table on the lvs-04:

[[email protected] ~]# ip ro
10.8.8.0/24 dev eth1  proto kernel  scope link  src 10.8.8.34
169.254.0.0/16 dev eth1  scope link  metric 1002
default via 10.8.8.30 dev eth1

LVS Router Installation

Configure LVS-01 Node

Enable IP forwarding:

# sed -i 's/net.ipv4.ip_forward = 0/net.ipv4.ip_forward = 1/' /etc/sysctl.conf
# sysctl -p

Install ipvsadm and Piranha packages:

# yum install -y piranha ipvsadm

Ensure the IP Virtual Server Netfilter kernel module is loaded:

# modprobe ip_vs

Set a password for the Piranha configuration tool:

# /usr/sbin/piranha-passwd

Once the password has been set, start the piranha-gui service:

# /etc/init.d/piranha-gui start

Note that we do not need to start the pulse service until configuration using the Piranha configuration tool is complete.

On the LVS routers, there are four services which need to be set to activate at boot time:

# chkconfig piranha-gui on
# chkconfig pulse on
# chkconfig iptables on
# chkconfig sshd on

Iptables service is required for multi-port services and firewall marks. SSH service is for remote logins and should be self explanatory I think.

Add a firewall rule to allow HTTP access to Piranha WebUI:

# iptables -A INPUT -s 10.8.8.0/24 -p tcp --dport 3636 -j ACCEPT

Add a rule for traffic that we’re balancing (HTTP and HTTPS):

# iptables -A INPUT -p tcp -m multiport --dports 80,443 -j ACCEPT

Configure LVS-02 Node

Install ipvsadm:

# yum install -y ipvsadm

Enable services:

# chkconfig pulse on
# chkconfig iptables on
# chkconfig sshd on

Copy sysctl.conf from the lvs-01 node:

[[email protected] ~]# scp /etc/sysctl.conf [email protected]:/etc/

Add a rule for traffic that we’re balancing (HTTP and HTTPS):

# iptables -A INPUT -p tcp -m multiport --dports 80,443 -j ACCEPT

When finished configuring NAT routing with Piranha (see the following sections of the article), copy the lvs.cf file from the lvs-01 node:

[[email protected] ~]# scp /etc/sysconfig/ha/lvs.cf [email protected]:/etc/sysconfig/ha/

Multi-Port Services

We are going to use multi-port services (HTTP and HTTPS), therefore firewall marks to bundle together different, but related protocols, are required. However, the job of assigning firewall marks must be performed by the network packet filter, iptables, outside of Piranha configuration tool.

Assigning firewall marks on both routers, the lvs-01 and the lvs-02:

# iptables -t mangle -A PREROUTING -p tcp -d 10.10.1.30/32 -m multiport --dport 80,443 -j MARK --set-mark 80

Where 10.10.1.30 is our public virtual IP address. Save iptables rules so that they get restored after a reboot:

# service iptables save

LVS NAT Routing Configuration with Piranha

Navigate a web browser to http://10.8.8.31:3636/.

Configure the primary server and pick a NAT network type. Provide NAT router details. 10.8.8.30 is our NAT virtual IP.

Add and configure a virtual server. 10.10.1.30 is our public virtual IP address. Firewall mark is used to bundle HTTP connections on port 80 and HTTPS connections on port 443.

Persistence is like a timer. It is set to 30 seconds. When a client connects to a service, LVS remembers the last connection for 30s.

Add and activate the real servers.

Configure redundancy by adding the lvs-02 node’s IP address.

Now, when everything is configured and saved, start the pulse service on the lvs-01 node:

# service pulse start

At this point we should be able to browse the public virtual IP 10.10.1.30 via both HTTP and HTTPS. Start the pulse service on the lvs-02 node. It should act as a backup node.

Check LVS status on the active lvs-01 node:

# ipvsadm -ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port      Forward Weight ActiveConn InActConn
FWM  80 wlc persistent 30
  -> 10.8.8.33:80            Masq    1      1          14
  -> 10.8.8.34:80            Masq    1      0          34

lvs.cf

Content of the /etc/sysconfig/ha/lvs.cf is shown below for referencing purposes.

[[email protected] ~]# cat /etc/sysconfig/ha/lvs.cf
serial_no = 3
primary = 10.10.1.31
service = lvs
backup_active = 1
backup = 10.10.1.32
heartbeat = 1
heartbeat_port = 539
keepalive = 2
deadtime = 6
network = nat
nat_router = 10.8.8.30 eth1:0
nat_nmask = 255.255.255.0
debug_level = NONE
monitor_links = 1
syncdaemon = 0
virtual http_server {
     active = 1
     address = 10.10.1.30 eth0:1
     vip_nmask = 255.255.255.255
     fwmark = 80
     port = 80
     persistent = 30
     send = "GET / HTTP/1.0\r\n\r\n"
     expect = "HTTP"
     use_regex = 0
     load_monitor = none
     scheduler = wlc
     protocol = tcp
     timeout = 6
     reentry = 15
     quiesce_server = 0
     server lvs-03 {
         address = 10.8.8.33
         active = 1
         weight = 1
     }
     server lvs-04 {
         address = 10.8.8.34
         active = 1
         weight = 1
     }
}

References

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/Load_Balancer_Administration/index.html
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/3/html/Cluster_Administration/s1-lvs-block-diagram.html

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