URL Load Balancing Using One Arm Mode with Source NAT on the Cisco Application Control Engine Configuration Example
Configure basic load balancing (Layer 3) where client traffic enters on one VLAN and Network Address Translation (NAT) is used when sending the client request out the same VLAN to the servers. The servers will respond to the Cisco® Application Control Engine (ACE), where the server’s IP is replaced with the VIP and the response message is sent to the client via the multilayer switch feature card (MSFC). The serverfarm for each request will be chosen based on the URL being requested.
Clients will send application requests through the MFSC, which routes them to a virtual IP address (VIP) within ACE. The VIP used in this example resides in an ACE context, which is configured with a single VLAN to handle client and server communication (Figure 1.). Client requests will arrive at the VIP and the Cisco ACE will pick the appropriate server to handle the request. ACE will rewrite the destination IP to that of the rserver and rewrite the source IP with one from a nat-pool. Once the client request is fully NAT’d it will be sent to the server over the same VLAN which it was originally received. The server will respond to the Cisco ACE, based on the source IP of the request. The Cisco ACE will receive the response, change the source IP to be the VIP, and send it to the MSFC. The MSFC will forward the response to the client.
The Cisco ACE needs to be configured via access control lists (ACLs) to allow traffic into the Cisco ACE data plane. After the ACL checks are made, a service policy, which is applied to the interface, is used to classify traffic destined for the VIP. The VIP is associated with a load-balancing action within the multimatch policy. The load-balancing action tells the Cisco ACE how to handle traffic that has been directed to a VIP. In this example, all traffic is sent to a server farm, where it is distributed in round-robin fashion to one of five real servers. The Cisco ACE configuration occurs in layers, such that it builds from the real IPs to applying the VIP on an interface. Due to this layered structure, it is optimal to create the configuration by working backward from the way the flow is processed. Thus, to enable server load balancing you need to do the following:
- Enable ACLs to allow data traffic through the Cisco ACE device, as it is denied by default.
- Configure the IPs of the servers (define rservers).
- Group the real servers (create a server farm).
- Define the virtual IP address (VIP).
- Define how traffic is to be handled as it is received (create a policy map for load balancing).
- Associate a VIP to a handling action (create a multimatch policy map [a service policy])
- Create client- and server-facing interfaces.
- Apply the VIP and ACL permitting client connections to the interface (apply access group and service policy to interface).
To begin the configuration, create an access list for permitting client connections.
ACE-1/onearm(config)# access-list everyone extended permit ip any any ACE-1/onearm(config)# access-list everyone extended permit icmp any any
The Cisco ACE needs to know the IP address of the servers available to handle client connections. The rserver command is used to define the IP address of the service. In addition, each rserver must be place in service for it to be used. The benefit of this design is that no matter how many applications or services an rserver hosts, the entire real server can be completely removed from the load-balancing rotation by issuing a single “no inservice” or “no inservice-standby” command at the rserver level. This is very beneficial for users needing to upgrade or patch an rserver, because they no longer have to go to each application and remove each instance of the rserver.
ACE-1/onearm(config)# rserver lnx1 ACE-1/onearm(config-rserver-host)# ip add 192.168.5.11 ACE-1/onearm(config-rserver-host)# inservice ACE-1/onearm(config-rserver-host)# rserver lnx2 ACE-1/onearm(config-rserver-host)# ip add 192.168.5.12 ACE-1/onearm(config-rserver-host)# inservice ACE-1/onearm(config-rserver-host)# rserver lnx3 ACE-1/onearm(config-rserver-host)# ip add 192.168.5.13 ACE-1/onearm(config-rserver-host)# inservice ACE-1/onearm(config-rserver-host)# rserver lnx4 ACE-1/onearm(config-rserver-host)# ip add 192.168.5.14 ACE-1/onearm(config-rserver-host)# inservice ACE-1/onearm(config-rserver-host)# rserver lnx5 ACE-1/onearm(config-rserver-host)# ip add 192.168.5.15 ACE-1/onearm(config-rserver-host)# inservice
Now group the rservers to be used to handle client connections into a server farm. Again, the rserver must be placed in service. This allows a single instance of an rserver to be manually removed from rotation.
ACE-1/routed(config)# serverfarm webfarm ACE-1/routed(config-sfarm-host)# rserver lnx1 ACE-1/routed(config-sfarm-host-rs)# inservice ACE-1/routed(config-sfarm-host-rs)# rserver lnx2 ACE-1/routed(config-sfarm-host-rs)# inservice ACE-1/routed(config)# serverfarm imagefarm ACE-1/routed(config-sfarm-host)# rserver lnx3 ACE-1/routed(config-sfarm-host-rs)# inservice ACE-1/routed(config-sfarm-host-rs)# rserver lnx4 ACE-1/routed(config-sfarm-host-rs)# inservice ACE-1/routed(config-sfarm-host-rs)# exit
Use a class-map to define the VIP where clients will be sending their requests.
ACE-1/onearm(config)# class-map slb-vip ACE-1/onearm(config-cmap)# match virtual-address 172.16.5.101 any
Next define an http class to match URLs requesting images. This is done using a simple http url match on the /image/ directory name. The wildcard allows for any image filename to be matched.
ACE-1/onearm(config)# class-map type http loadbalance match-all images ACE-1/onearm(config-cmap-http-lb)# match http url /images/.*
Next define the action to take when a new client request arrives. In this case we have two possible actions, based on the http matching class defined above requests for images will be sent to the imagefarm, while all other requests will be sent to the web servers in the webfarm.
ACE-1/onearm(config)# policy-map type loadbalance http first-match slb-logic ACE-1/onearm(config-pmap-lb)# class images ACE-1/onearm(config-pmap-lb-c)# serverfarm imagefarm ACE-1/onearm(config-pmap-lb-c)# class class-default ACE-1/onearm(config-pmap-lb-c)# serverfarm webfarm
Since the VIPs and load-balancing actions are defined independently, they must be associated so that the Cisco ACE knows how to handle traffic destined for a VIP. The association is made using a multimatch policy map. Keep in mind that multimatch policy maps are applied to interfaces as service policies. “nat dynamic” is configured to make the Cisco ACE source NAT all client requests. The nat-pool will be defined in a later step.
ACE-1/onearm(config)# policy-map multi-match client-vips ACE-1/onearm(config-pmap)# class slb-vip ACE-1/onearm(config-pmap-c)# loadbalance policy slb ACE-1/onearm(config-pmap-c)# loadbalance vip inservice ACE-1/onearm(config-pmap-c)# nat dynamic 5 vlan 50
At this point the interface VLAN can be created to interconnect the Cisco ACE to the network.
ACE-1/onearm(config)# interface vlan 50 ACE-1/onearm(config-if)# description “Client-Sever VLAN” ACE-1/onearm(config-if)# ip address 172.16.5.5 255.255.255.0 ACE-1/onearm(config-if)# no shutdown
The last step is to apply the ACL and service policy (policy-map multi-match) to the client side interface. Both the access group and service policy are applied on the input side of the interface. The nat-pool is also created, for use in the multi-match policy.
ACE-1/onearm(config)# interface vlan 50 ACE-1/onearm(config-if)# access-group input everyone ACE-1/onearm(config-if)# service-policy input client-vips ACE-1/onearm(config-if)# nat-pool 5 172.16.5.200 172.16.5.209 netmask 255.255.255.0 pat
|Note:||There is no need to add an access group to the server side, as the Cisco ACE automatically creates pinholes to allow server response traffic to pass back to the client.|
When a client connects to the VIP they download the index.html page from the webfarm servers and all the embedded images from the imagefarm servers. This can be verified using the detailed output of the show service-policy command:
ACE-1/onearm# show service-policy client-vips detail Status : ACTIVE Description: - ----------------------------------------- Interface: vlan 50 service-policy: client-vips class: slb-vip nat: nat dynamic 5 vlan 50 curr conns : 0 , hit count : 83 dropped conns : 2 client pkt count : 524 , client byte count: 45320 server pkt count : 558 , server byte count: 146197 conn-rate-limit : 0 , drop-count : 0 bandwidth-rate-limit : 0 , drop-count : 0 VIP Address: Protocol: Port: 172.16.5.101 tcp eq 80 loadbalance: L7 loadbalance policy: slb-logic VIP Route Metric : 77 VIP Route Advertise : DISABLED VIP ICMP Reply : DISABLED VIP State: INSERVICE curr conns : 0 , hit count : 0 dropped conns : 0 client pkt count : 0 , client byte count: 0 server pkt count : 0 , server byte count: 0 conn-rate-limit : 0 , drop-count : 0 bandwidth-rate-limit : 0 , drop-count : 0 L7 Loadbalance policy : slb-logic class/match : images LB action : primary serverfarm: imagefarm state: UP backup serverfarm : - hit count : 20 dropped conns : 0 class/match : class-default LB action : primary serverfarm: webfarm state: UP backup serverfarm : - hit count : 5 dropped conns : 0
Related show Commands
This section provides information you can use to confirm your configuration is working properly.
Certain show commands are supported by the Output Interpreter Tool (registered customers only), which allows you to view an analysis of show command output.
ACE-1/onearm #show arp ACE-1/onearm #show acl ACE-1/onearm #show service-policy client-vips ACE-1/routed# show service-policy client-vips detail ACE-1/onearm #show serverfarm ACE-1/onearm #show rserver ACE-1/onearm #show stats
Once you’ve completed the configuration, verify that the Cisco ACE has an Address Resolution Protocol (ARP) response for each rserver and the default route to the client. Check the ACL hits to ensure that client connections are being accepted. Check the service policy output to see the client connection hits, and verify that the server is responding with response packets. The “show” command for serverfarm and rserver can be used to display the exact rserver handling the connection and the amount of work the entire server farm has handled. The “show stats” command provides a higher level of monitoring of ACE load balancing, inspection, probes, and other important metrics.
ACE-1/onearm# sho run Generating configuration.... access-list everyone line 8 extended permit ip any any access-list everyone line 16 extended permit icmp any any rserver host lnx1 ip address 192.168.5.11 inservice rserver host lnx2 ip address 192.168.5.12 inservice rserver host lnx3 ip address 192.168.5.13 inservice rserver host lnx4 ip address 192.168.5.14 inservice rserver host lnx5 ip address 192.168.5.15 inservice serverfarm host web rserver lnx1 inservice rserver lnx2 inservice rserver lnx3 inservice rserver lnx4 inservice rserver lnx5 inservice class-map match-all slb-vip 2 match virtual-address 172.16.5.100 any policy-map type management first-match remote-access class class-default permit policy-map type loadbalance http first-match slb class class-default serverfarm web policy-map multi-match client-vips class slb-vip loadbalance vip inservice loadbalance policy slb nat dynamic 5 vlan 50 interface vlan 50 description "Client-Server VLAN" ip address 172.16.5.5 255.255.255.0 access-group input everyone service-policy input client-vips service-policy input remote-access nat-pool 5 172.16.5.200 172.16.5.209 netmask 255.255.255.0 pat no shutdown ip route 0.0.0.0 0.0.0.0 172.16.5.1