This document outlines the steps to configure a load balanced web server cluster with high availability using Pacemaker on CentOS 7. It describes preparing three identical web servers, installing and configuring two load balancers with Apache and mod_proxy_balancer, and setting up Pacemaker to cluster the load balancers and migrate resources between them for high availability. Key resources configured in Pacemaker include a shared virtual IP address and the Apache service. The document provides commands to authorize, initialize, and test the two-node Pacemaker cluster.

1. The Free Enterprise
Load Balancer
Mike Soule

2. Goals
• High Availability
• Scalability
• Performance
• Maintainability

3. Goals: From…
www

4. Goals: To…
balancer
www www www

5. Web Server Preparation
• Three Identical Web Servers
- IPs: 10.47.47.101-103
- Default page (index.html) to identify
which web server
- Open http port (80)

6. Web Server Preparation

7. Load Balancer Preparation
• Load Balancer Server
- CentOS 7 minimal
- IP: 10.47.47.11
- Packages: httpd mod_ssl openssl
- Ports: http, https (80, 443)
# yum install httpd mod_ssl openssl
# firewall-cmd --permanent --add-service=http
# firewall-cmd --permanent --add-service=https
# firewall-cmd --reload

8. Configure Web Server Pool
• Using mod_proxy_balancer
- Included in default Apache install
# vim /etc/httpd/conf.d/proxy_balancer.conf
<IfModule mod_proxy_balancer.c>
<Proxy balancer://www-cluster>
BalancerMember http://10.47.47.101:80
BalancerMember http://10.47.47.102:80
BalancerMember http://10.47.47.103:80
ProxySet timeout=300
</Proxy>
ProxyPass / balancer://www-cluster
</IfModule>

9. SELinux
• New files in /etc/httpd may cause
errors due to SELinux contexts
• Disabling SELinux is NEVER the
answer!
• A few minutes of Google-ing will reveal
a solution…
# restorecon -RvF /etc/httpd/

10. Test and Start Apache
# apachectl configtest
# systemctl enable httpd
# systemctl start httpd

11. The Balancer Manager
• Balancer Manager is a built-in web
interface for managing the web server
pool
• Status checks must be enabled
# vim /etc/httpd/conf.d/status.conf
ExtendedStatus On
<Location /server-status>
SetHandler server-status
Require host localhost
</Location>

12. The Balancer Manager
• Enable the balancer manager
# vim /etc/httpd/conf.d/proxy_balancer.conf
• Add before other ProxyPass directive…
ProxyPass /balancer-manager !
• Add under Proxy Pass directives
<Location /balancer-manager>
SetHandler balancer-manager
</Location>

13. But wait, we created a
single point of failure…
#OMGWTFBBQ!

14. Single Point of Failure
balancer
www www www

15. Clustered Load Balancers
balancer balancer
www www www

16. Clustered Load Balancers
balancer balancer
www www www

17. Clustered Load Balancers
• IP of new server: 10.47.47.12
• Setup on both load balancers…
# yum install pcs
# firewall-cmd --permanent --add-service=high-availability
# firewall-cmd —reload
# echo “10.47.47.11 bar-lb-01” >> vim /etc/hosts
# echo “10.47.47.12 bar-lb-02” >> vim /etc/hosts

18. Pacemaker Config System
• Set a password for the hacluster user
(on both load balancers)
# passwd hacluster
• Set boot services and start pcs (on
both load balancers)
# systemctl disable httpd
# systemctl stop httpd
# systemctl enable pcsd
# systemctl start pcsd

19. Starting the Cluster
• From here, all commands on one load
balancer only (they will be automatically
replicated to the second load balancer)
# pcs cluster auth bar-lb-01 bar-lb-02 -u hacluster
# pcs cluster setup --name lb-cluster bar-lb-01 bar-lb-02
# pcs cluster start --all

20. Two-node Cluster Setup
• Global cluster settings…
# pcs property set stonith-enabled=false
# pcs property set no-quorum-policy=ignore
# pcs property set default-resource-stickiness=1
# pcs property set start-failure-is-fatal=false
# pcs property set stop-orphan-actions=true
# pcs property set stop-orphan-resources=true
# pcs resource defaults migration-threshold=1
# pcs resource op defaults timeout=60s

21. Cluster Resources
• Shared IP Address (10.47.47.10)
# pcs resource create ClusterIP IPaddr2 ip=10.47.47.10
cidr_netmask=32 op monitor interval=15s
• Apache
# pcs resource create ApacheLB apache params
configfile=/etc/httpd/conf/httpd.conf
statusurl="http://localhost/server-status" op monitor
interval=30s

22. Resource Sanity
• Resource location and order sanity
# pcs property set symmetric-cluster=true
# pcs constraint order set ClusterIP ApacheLB
# pcs constraint colocation add ApacheLB with ClusterIP
score=INFINITY

23. Review and Test
• View the cluster status
# pcs status
• View the cluster config
# pcs config
• Test failover
# pcs cluster standby <node>
# pcs cluster unstandby <node>

24. Cluster Web UI
• https://10.47.47.11:2224/