Keepalived

Keepalived Loadbalancer

Introduction

This page contains a basic description about how to set up keepalived.

The example on this page is specific to debian. However, it should be possible to adjust it to other distributions.

Keepalived mode is Direct Routing.

It is required that the keepalived node(s) and the nodes for which it is loadbalancing on the same network segment. There must be no firewall between those hosts. Be careful: some virtualization systems do loadbalancing by themselves.

For more information please see: www.keepalived.org or the man keepalived.conf (which is much more helpful than the web pages).

Software installation

Packages are installed using

# apt-get install keepalived 

Keepalived requires some kernel modules to be loaded. They are loaded by the ipvsadmm service. So we enable it using dpkg-reconfigure:

# dpkg-reconfigure ipvsadm

Answer the questions with "Yes" ("load ... at boot") and then "backup" for "Daemon method".

Enable IP forwarding on the keepalived node: configure in /etc/sysctl.conf:

net.ipv4.ip_forward=1

Enable this by either rebooting or by issuing sysctl -w net.ipv4.ip_forward=1.

Configuration example: HTTP

Keepalived configuration file

Create a file

/etc/keepalived/keepalived.conf

with following contend (adapt network adresses)

global_defs {
    router_id OX
}

vrrp_sync_group OX_GROUP {
    group {
        OX_GOUP
    }
}

vrrp_instance OX_VRRP {
    state BACKUP
    interface eth0
    garp_master_delay 10
    virtual_router_id 10
    priority 101
    nopreempt
    advert_int 1
    authentication {
        auth_type AH   # Simple 'PASS' can use
        auth_pass 1234 # example password '1234' 
    }
    virtual_ipaddress {
        10.20.30.77/24 brd 10.20.30.255 dev eth0 # virtual service ip 10.20.30.67
    }
    virtual_ipaddress_excluded {
    }
}

virtual_server_group OX_HTTP {
        10.20.30.77 80         # virtual ip and port 80
}

virtual_server_group OX_OL_PUSH {
        10.20.30.77 44335      # VIP VPORT
}

virtual_server group OX_HTTP {
    delay_loop 3
    lvs_sched  rr
    lvs_method DR
    protocol   TCP
    virtualhost 10.20.30.77

    real_server 10.20.30.123 80 {
        weight 1
        inhibit_on_failure
        HTTP_GET {
            url {
                path /servlet/TestServlet
                status_code 200
            } 
            connect_port 80
            connect_timeout 10
        }
    }

    real_server 10.20.30.321 80 {
        weight 1
        inhibit_on_failure
        HTTP_GET {
            url {
                path /servlet/TestServlet
                status_code 200
            }
            connect_port 80
            connect_timeout 10
        }
    } 
}

virtual_server group OX_OL_PUSH {
    delay_loop 3
    lvs_sched  rr
    lvs_method DR
    protocol   UDP

    real_server 10.20.30.123 44335 {
        weight 1
        inhibit_on_failure
	  TCP_CHECK {
                 connect_port 9999
		  connect_timeout 5
        }
    }

    real_server 10.20.30.321 44335 {
        weight 1
        inhibit_on_failure
        TCP_CHECK {
                 connect_port 9999
		  connect_timeout 5
        }
    }
}

Configuration example: Keepalived for Galera Loadbalancing

Keepalived configuration

In this example we have the following networking information:

• loadbalancer IP 10.20.29.174
• Three galera nodes: 10.20.29.140, 10.20.29.142, 10.20.29.138

Then the keepalived configuration file /etc/keepalived/keepalived.conf looks as follows:

global_defs {
  # This should be unique.
  router_id galera-lb
}

vrrp_instance mysql_pool {
  # The interface we listen on.
  interface eth0

  # The default state, one should be master, the others should be set to SLAVE.
  state MASTER
  priority 101

  # This should be the same on all participating load balancers.
  virtual_router_id 19

  # Set the interface whose status to track to trigger a failover.                   
  track_interface {           
    eth0
  }

  # Password for the loadbalancers to share.
  authentication {
    auth_type PASS
    auth_pass Twagipmiv3
  }

  # This is the IP address that floats between the loadbalancers.
  virtual_ipaddress {
   10.20.29.174/32 dev eth0
  }
}

# Here we add the virtal mysql node
virtual_server 10.20.29.174 3306 {
  delay_loop 6
  # Round robin, but you can use whatever fits your needs.
  lb_algo rr
  lb_kind DR
  protocol TCP

  # For each server add the following. 
  real_server 10.20.29.140 3306 {
    weight 10
    MISC_CHECK {
      misc_path "/etc/keepalived/galera-checker.pl 10.20.29.140"
      misc_timeout 5
    }
  }
  real_server 10.20.29.142 3306 {
    weight 11
    MISC_CHECK {
      misc_path "/etc/keepalived/galera-checker.pl 10.20.29.142"
      misc_timeout 5
    }
  }
  real_server 10.20.29.138 3306 {
    weight 12
    MISC_CHECK {
      misc_path "/etc/keepalived/galera-checker.pl 10.20.29.138"
      misc_timeout 5
    }
  }
}

Here we have configured a galera-specific node health checker. This is a custom perl script.

The script requires some perl module for DB access:

# apt-get install libdbd-mysql-perl

The script is expected in /etc/keepalived/galera-checker.pl and looks like this:

#!/usr/bin/perl

# dominik.epple@open-xchange.com, 2013-06-10

use strict;
use warnings;

#
# config section
#
our $username="some_db_user";
our $password="some_db_pass";
our $debug=0;

our %checks=(
  #"wsrep_cluster_size" => "3",
  "wsrep_ready" => "ON",
  "wsrep_local_state" => "4" # Synced
);
#
# config section end
#

our $host=$ARGV[0] or die "usage: $0 <IP of galera node>"; 

use DBI;
our $dbh = DBI->connect("DBI:mysql:configdb;host=$host", $username, $password
                   ) || die "Could not connect to database: $DBI::errstr";

our $results = $dbh->selectall_hashref("show status like '%wsrep%'", 'Variable_name') or die "Error trying to selectall_hashref";

our %cr=();

foreach my $id (keys %$results) {
  $::cr{$id}=$results->{$id}->{"Value"};
}

$dbh->disconnect();

for my $k (keys %checks) {
  if(exists $::cr{$k}) {
    if($::checks{$k} ne $::cr{$k}) {
      print STDERR "$0: warning: mismatch in $k: expected $::checks{$k}, got $::cr{$k}\n";
      exit(1);
    }
    else {
      print STDERR "$0: info: match in $k: expected $::checks{$k}, got $::cr{$k}\n" if($::debug);
    }
  }
  else {
    print STDERR "$0: warning: no check result for $k (want $::checks{$k})\n";
  }
}

exit(0);

Adding a second Keepalived node for redundancy

Set up a second Keepalived node as described above, with the following changes to the configuration file /etc/keepalived/keepalived.conf:

• Change the router_id (to the hostname, for example)
• Change the state to BACKUP
• Change the priority to something lower than the masters priority (e.g. 100)

Make sure the virtual_router_id and authentication information is the same on the backup keepalived node as on the master keepalived node.

Now the backup node will notice the master going down and take over. Automatic failback also happens.

Networking adjustments for the galera nodes

The galera nodes need the loadbalancer IP configured on some network device in order for galera to be able to bind on this device.

However, creating a fully configured "alias" device is bad, since the galera nodes will pick the loadbalancer IP as primary IP of the node for example for full state transfers (SST). So when trying a SST the galera nodes will try to connect to the loadbalancer on the SST port. This will fail because on the loadbalancer nothing listens on the SST port.

If we instead create a dummy device and only assign an IP to it (without setting all those flags like UP), then galera can bind to the IP, but it won't use the IP as its primary IP. A configuration like this can be created using the following trick. Ad dsome pre-up, post-up, pre-down, post-down lines to the /etc/network/interfaces file as follows:

allow-hotplug eth0
iface eth0 inet dhcp
    pre-up echo 1 > /proc/sys/net/ipv4/conf/all/arp_ignore
    pre-up echo 2 > /proc/sys/net/ipv4/conf/all/arp_announce
    post-up ip addr add 10.20.29.174/32 dev dummy0
    pre-down ip addr del 10.20.29.174/32 dev dummy0
    post-down echo 0 > /proc/sys/net/ipv4/conf/all/arp_ignore
    post-down echo 0 > /proc/sys/net/ipv4/conf/all/arp_announce