Coyote Point Systems' Equalizer E450si Load Balancer

Coyote Point's technology uses NAT (network address translation) to assign a single IP address to a cluster of servers. NAT also lets the device's virtual cluster operate independently of the servers and their applications. Equalizer's NAT operation modifies inbound and outbound packets without additional configuration. All you do is set the default route for servers to Equalizer's internal IP address.

Cluster Config

From Equalizer's Web management interface, I configured clusters and load balancing. I used Internet Explorer 6, but you can use any browser that supports JavaScript. After logging in with read/write access (view-only access is also available), I set up a virtual cluster using a TCP Layer 4 algorithm.

I gave the virtual cluster an IP address associated with the external network and assigned it to TCP Port 80 to load balance HTTP traffic. Additional port assignments per cluster aren't available, but various options for load balancing are.

I set a round-robin load-balancing policy. Other options include distributing the load by static weights applied to servers; by adaptive weights depending on server response times and active connections; by the servers with the fastest response times; or by the servers with the fewest connections. You also can install an optional server agent to orchestrate load balancing, but there's no option to use SNMP or to configure virtual LANs in the load-balancing algorithm. The vendor says options for these will be added later. Coyote Point Envoy, a $3,995-per-site add-on, lets you use the clients' geographical location for load balancing.

I also examined the options, or flags, to the virtual cluster configuration. Flags give servers in the cluster additional information. I enabled spoofing so Equalizer would present the actual IP address of clients to the server. That way, I could verify the load-balancing algorithms using the client requests logged on the target servers from Apache Web server access logs. I disabled a persistence flag that would otherwise insert session-persistence cookies into the data returned to clients and use those cookies to direct clients back to a single server--cookies are good if you're running an e-commerce site, but bad if you're testing round-robin load balancing.

Once my virtual cluster configuration was set, I committed it to memory and turned my attention to adding servers to the cluster.

Sharing the Load

After adding a server to my HTTP virtual cluster, I fired up Spirent Avalanche. Avalanche simulated 150 to 300 clients, generating 50 transactions (get requests) per TCP connection (see preformance chart, below). The one server in the cluster started dropping requests after I ramped up 150 simultaneous users. As more users clamored for Web pages, the average response time for each request deteriorated. When I reached 200 users requesting pages, the lone server dropped 123 transactions.

I added a second server to the virtual cluster and gave it the same weight as the first server for even round-robin load balancing. The two servers easily handled up to 300 users generating 50 transactions per TCP session. And response time was better than one server with only 150 users connected. The access logs showed Equalizer was living up to its name: It balanced the traffic between the servers and gave each server equal access to clients.Hot Spare Is Only Warm

I set up a third Solaris server (UltraSPARC-IIe 500-MHz) in my HTTP cluster as a hot spare. Then, while traffic was being generated to the original two servers in the cluster, I unplugged one. Although it took approximately 30 seconds to shift traffic to the hot spare, Equalizer didn't drop any transactions. Still, the handoff should be speedier.

I set up virtual clusters for other TCP services, including FTP, SSH, and telnet, and Equalizer easily distributed the load. I also investigated Equalizer's ability to parse requests at Layer 7. I created an HTTP Virtual Cluster and rules that dedicated one of my clustered servers to serve up images. Using rules, I could match on file, directory and path names and even replace text in HTTP headers to balance the load. When a page was requested, one server was dedicated to processing images while the rest of the servers balanced the load for other page requests.

Equalizer also supports SSL load balancing by performing encryption and decryption. It passes requests and receives responses from clustered servers in clear text and encrypts the traffic between itself and clients. Hence, you need only one certificate per HTTPS virtual cluster. If you need to add SSL acceleration, Coyote Point can add its XCEL SSL PCI card for $3,499.

A remote syslog server is supported to export events. Although you can view events from the Web console, the display is tiny under a normal Web browser view. Reports are limited to plotting graphs for virtual clusters or individual servers. Plots are available for server connections, service times, active connections and hit rates from the past five minutes to the past two days, but you can't export the underlying data to CSV, HTTP or PDF for later use.The Equalizer is a no-fuss appliance solution for cluster management and load balancing at a bargain price. If you're worried about high availability, the Coyote Point team has hot-spare configurations that replicate cluster configurations to a backup unit automatically.

Sean Doherty is a senior technology editor and lawyer based at our Syracuse University Real-World Labs®. Write to him at [email protected].