RHEL7: Configure a high available load-balancer.

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For this tutorial, you need 2 virtual/physical servers for the load-balancers and 2 virtual/physical servers to load-balance.

Note: Additional configuration will be required to run HAProxy on the Red Hat OpenStack Platform (see the OpenStack Networking Guide for more information).

In addition to the 4 IP addresses needed by the servers themselves, a fifth virtual IP address (VIP) is necessary. The two load-balancers and the VIP need to be in the same network segment.

Piranha has been replaced in RHEL7 with HAProxy and keepalived. For this reason, HAProxy will be used as load-balancing software, keepalived as high availability solution and apache as software to load-balance.

Here is the addressing schema chosen to write into the /etc/hosts file of each server:

  • vip
  • haproxy1
  • haproxy2
  • httpd1
  • httpd2

HAProxy Installation

On the haproxy1/haproxy2 servers, execute the following instructions:

Install the HAProxy package:

# yum install -y haproxy

Edit the /etc/haproxy/haproxy.cfg file, replace the line “frontend  main *:5000” with “frontend  main *:80” and comment out the line “use_backend static if url_static“.
At the end of the same file, remove the lines starting with “server app” and replace them with the following lines:

server httpd1 check
server httpd2 check

Activate at boot and start the HAProxy service:

# systemctl enable haproxy
# systemctl start haproxy

Create the /etc/firewalld/services/haproxy.xml file and paste the following lines:

<?xml version="1.0" encoding="utf-8"?>
<description>HAProxy load-balancer</description>
<port protocol="tcp" port="80"/>

Assign correct SELinux context and file permissions to the haproxy.xml file:

# cd /etc/firewalld/services
# restorecon haproxy.xml
# chmod 640 haproxy.xml

Update the firewall configuration:

# firewall-cmd --permanent --add-service=haproxy
# firewall-cmd --reload

Keepalived Installation

On the haproxy1/haproxy2 servers, execute the following instructions:

Install the keepalived package:

# yum install -y keepalived

Create a new /etc/keepalived/keepalived.conf file and paste the following lines:

vrrp_script chk_haproxy {
  script "killall -0 haproxy" # check the haproxy process
  interval 2 # every 2 seconds
  weight 2 # add 2 points if OK

vrrp_instance VI_1 {
  interface eth0 # interface to monitor
  state MASTER # MASTER on haproxy1, BACKUP on haproxy2
  virtual_router_id 51
  priority 101 # 101 on haproxy1, 100 on haproxy2
  virtual_ipaddress { # virtual ip address 
  track_script {

Activate at boot and start the keepalived service:

# systemctl enable keepalived
# systemctl start keepalived

Check the presence of the VIP on the haproxy1 server:

# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 52:54:00:f7:2a:a9 brd ff:ff:ff:ff:ff:ff
inet brd scope global eth0
valid_lft forever preferred_lft forever
inet scope global eth0
valid_lft forever preferred_lft forever
inet6 fe80::5054:ff:fef7:2aa9/64 scope link
valid_lft forever preferred_lft forever

Apache Installation

On the httpd1/httpd2 servers, follow the instructions for the Apache installation.
Create a file called index.html in the /var/www/html directory on the httpd1 server and paste the following line:

Test httpd1

Do the same operation on the httpd2 server but replace “httpd1” with “httpd2” in the index.html file.

From another server, test the configuration:

# yum install -y elinks
# elinks

HAProxy Intricacies

In some cases, because HaProxy tries to bind to an IP address that doesn’t exist on any interfaces, it doesn’t start and displays an error message like “Starting proxy stats: cannot bind socket“.

The solution is to create a file called /etc/sysctl.d/10-haproxy.conf and paste the following line:


Then, update the configuration:

# sysctl -p

Note1: There is a page dedicated to kernel runtime parameters assignment on this website.
Note2: Additional information about HAProxy boot errors and solutions can be found here.

In some cases, you also need to enable a SELinux boolean to allow HAProxy to bind to non standard ports:

# setsebool -P haproxy_connect_any on

Additional Resources

RedHat documentation provides a guide called RHEL 7 Load Balancer Administration.
Oracle Linux Administrator’s Guide for Release 7 provides a chapter dedicated to HAProxy configuration.
The RedHat CloudForms High Availability Guide provides a chapter about Configuring the HAProxy Load-Balancer.

Note: HAProxy 1.8 is not currently available for RHEL 7 due to a syntax change introduced in this version, breaking the compatibility when parsing the configuration file. Red Hat doesn’t want his customers to experience a production outage after a simple HAProxy upgrade (see details here).

The official HAProxy website offers many interesting articles:

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For HAProxy it’s nice to say that it supports a Active-Backup mode.
For example you can have 1 front-end and 1 back-end (multiple front-, back-ends are possible) listening on specific port and to define 1 (or more servers) as primary and 1 (or more for backup) connection. When all primary servers fall down, HAPRoxy will use the backup servers.
Also HAProxy has a Web statistics page to keep an eye on the usage of every interface.

RHCSA7: Task of the day

Allowed time: 3 minutes.
Check that you've got no SELinux policy violations.

RHCE7: Task of the day

Allowed time: 5 minutes.
Set up time synchronization with default configuration.

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