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> Chapter 25 - Server Load Balancing > Example HTTP load balancing to three real web servers

Example HTTP load balancing to three real web servers

In this example, a virtual web server with IP address 192.168.37.4 on the Internet, is mapped to three real web servers connected to the FortiGate unit dmz1 interface. The real servers have IP addresses 10.10.123.42, 10.10.123.43, and 10.10.123.44. The virtual server uses the First Alive load balancing method. The configuration also includes an HTTP health check monitor that includes a URL used by the FortiGate unit for get requests to monitor the health of the real servers.

Connections to the virtual web server at IP address 192.168.37.4 from the Internet are translated and load balanced to the real servers by the FortiGate unit. First alive load balancing directs all sessions to the first real server. The computers on the Internet are unaware of this translation and load balancing and see a single virtual server at IP address 192.168.37.4 rather than the three real servers behind the FortiGate unit.

Virtual server configuration example

Web-based manager configuration

Use the following procedures to configure this load balancing setup from the web-based manager.

To add an HTTP health check monitor

In this example, the HTTP health check monitor includes the URL “/index.html” and the Matched Phrase “Fortinet products”.

  1. Go to Policy & Objects > Health Check.
  2. Select Create New.
  3. Add an HTTP health check monitor that sends get requests to http://<real_server_IP_address>/index.html and searches the returned web page for the phrase “Fortinet products”.
Name HTTP_health_chk_1
Type HTTP
Port 80
URL /index.html
Matched Content Fortinet products
Interval 10 seconds
Timeout 2 seconds
Retry 3
  1. Select OK.
To add the HTTP virtual server
  1. Go to Policy & Objects > Virtual Servers.
  2. Select Create New.
  3. Add an HTTP virtual server that allows users on the Internet to connect to the real servers on the internal network. In this example, the FortiGate wan1 interface is connected to the Internet.
Name Load_Bal_VS1
Type HTTP
Interface wan1
Virtual Server IP 192.168.37.4

The public IP address of the web server.

The virtual server IP address is usually a static IP address obtained from your ISP for your web server. This address must be a unique IP address that is not used by another host and cannot be the same as the IP address of the external interface the virtual IP will be using. However, the external IP address must be routed to the selected interface. The virtual IP address and the external IP address can be on different subnets. When you add the virtual IP, the external interface responds to ARP requests for the external IP address.
Virtual Server Port 80
Load Balance Method First Alive
Persistence HTTP cookie
HTTP Multiplexing Select.

The FortiGate unit multiplexes multiple client into a few connections between the FortiGate unit and each real HTTP server. This can improve performance by reducing server overhead associated with establishing multiple connections.
Preserve Client IP Select

The FortiGate unit preserves the IP address of the client in the X-Forwarded-For HTTP header.
Health Check Move the HTTP_health_chk_1 health check monitor to the Selected list.
  1. Select OK.
To add the real servers and associate them with the virtual server
  1. Go to Policy & Objects > Real Servers.
  2. Select Create New.
  3. Configure three real servers that include the virtual server Load_Bal_VS1. Each real server must include the IP address of a real server on the internal network.
    Configuration for the first real server.
Virtual Server Load_Bal_VS1
IP Address 10.10.10.42
Port 80
Weight Cannot be configured because the virtual server does not include weighted load balancing.
Maximum Connections 0

Setting Maximum Connections to 0 means the FortiGate unit does not limit the number of connections to the real server. Since the virtual server uses First Alive load balancing you may want to limit the number of connections to each real server to limit the traffic received by each server. In this example, the Maximum Connections is initially set to 0 but can be adjusted later if the real servers are getting too much traffic.

Configuration for the second real server.

Virtual Server Load_Bal_VS1
IP Address 10.10.10.43
Port 80
Weight Cannot be configured because the virtual server does not include weighted load balancing.
Maximum Connections 0

Setting Maximum Connections to 0 means the FortiGate unit does not limit the number of connections to the real server. Since the virtual server uses First Alive load balancing you may want to limit the number of connections to each real server to limit the traffic received by each server. In this example, the Maximum Connections is initially set to 0 but can be adjusted later if the real servers are getting too much traffic.

Configuration for the third real server.

Virtual Server Load_Bal_VS1
IP Address 10.10.10.44
Port 80
Weight Cannot be configured because the virtual server does not include weighted load balancing.
Maximum Connections 0

Setting Maximum Connections to 0 means the FortiGate unit does not limit the number of connections to the real server. Since the virtual server uses First Alive load balancing you may want to limit the number of connections to each real server to limit the traffic received by each server. In this example, the Maximum Connections is initially set to 0 but can be adjusted later if the real servers are getting too much traffic.
To add the virtual server to a security policy

Add a wan1 to dmz1 security policy that uses the virtual server so that when users on the Internet attempt to connect to the web server’s IP address, packets pass through the FortiGate unit from the wan1 interface to the dmz1 interface. The virtual IP translates the destination address of these packets from the virtual server IP address to the real server IP addresses.

  1. Go to Policy & Objects > IPv4 Policy.
  2. Select Create New.
  3. Configure the security policy:
Policy Type Firewall
Policy Subtype Address
Incoming Interface wan1
Source Address all (or a more specific address)
Outgoing Interface dmz1
Destination Address Load_Bal_VS1
Schedule always
Service HTTP
Action ACCEPT
Log Allowed Traffic Select to log virtual server traffic
Enable NAT Select this option and select Use Destination Interface Address.
  1. Select other security policy options as required.
  2. Select OK.

CLI configuration

Use the following procedure to configure this load balancing setup from the CLI.

To configure HTTP load balancing
  1. Use the following command to add an HTTP health check monitor that sends get requests to http://<real_server_IP_address>/index.html and searches the returned web page for the phrase “Fortinet products”.

config firewall ldb-monitor

edit HTTP_health_chk_1

set type http

set port 80

set http-get /index.html

set http-match “Fortinet products”

set interval 10

set timeout 2

set retry 3

end

 

  1. Use the following command to add an HTTP virtual server that allows users on the Internet to connect to the real servers on the internal network. In this example, the FortiGate wan1 interface is connected to the Internet.

config firewall vip

edit Load-Bal_VS1

set type server-load-balance

set server-type http

set ldb-method first-alive

set http-multiplex enable

set http-ip-header enable

set extip 192.168.37.4

set extintf wan1

set extport 80

set persistence http-cookie

set monitor HTTP_health_chk_1

config realservers

edit 1

set ip 10.10.10.42

set port 80

next

edit 2

set ip 10.10.10.43

set port 80

next

edit 3

set ip 10.10.10.44

set port 80

end

end

 

  1. Use the following command to add a security policy that includes the load balance virtual server as the destination address.

config firewall policy

edit 0

set srcintf wan1

set srcaddr all

set dstintf dmz1

set dstaddr Load-Bal_VS1

set action accept

set schedule always

set service ALL

set nat enable

end

Configure other security policy settings as required.