Global Load Balancing 101

How it all works

Load Balancing has been around for many years. When most people think about Load Balancing, they think of an appliance, such as those from Cisco, F5, Citrix, Barracuda and others. These application-neutral devices present a “virtual server” IP address and service (such as HTTP) to the outside world and when users attempt to connect, it forwards the connection to the most appropriate real server doing bi-directional network address translation (NAT) in order to increase application availability.

Network-Based Load Balancing

Basic network-based load balancing works like this:

1. The user (client) connects to the Internet and requests a service (e.g. a website).
2. DNS routes the user to a specific IP address at a specific datacenter
3. The user is connected to the load balancer.
4. The load balancer accepts the connection, and after deciding which server (or host) should receive the connection, changes the destination IP (and possibly port) to match the service of the selected host.
5. The server accepts the connection and responds back to the original source, the client, via its default route, the load balancer.
6. The load balancer intercepts the return packet from the host and now changes the source IP (and possibly the port) to match the virtual server IP and port, and forwards the packet back to the client.
7. The client receives the return packet, believing that it came from the virtual server, and displays the content.

Figure 1: Traditional network-based load balancing diagram

Global Load Balancing

Global Load Balancing uses the same basic principle, except on a significantly larger scale. While the fundamental goal of spreading traffic across a range of servers still exists, Cloud Leverage Global Load Balancing takes it to the next level. We can't deny that there is a need for load balancing within the datacenter, but today there is an even greater need to extend the benefits of load balancing to a global audience, routing users and traffic to the nearest datacenter that can deliver the levels of application performance and availability they require.

Global load balancing works like this:

1. The user (client) connects to the Internet and requests a service (e.g. a website).
2. DNS routes the user to a specific IP address which is connected to the Cloud Leverage IP anycast network.
3. The user is connected to the closest, local Cloud Leverage node.
4. The Cloud Leverage node accepts the connection and, based on customer specified policy, decides which of the customer's datacenters to send the user to (based on performance, geography, etc.).
5. The user is directed to the customer's datacenter containing the desired application content.
6. Content is delivered to the user which appears to come from the local Cloud Leverage node. If a subscription to acceleration is active, content is fast-tracked across the Internet back to the user.
7. Additional network-based load balancing may still be used to spread the load over a server farm as above.

Figure 2: Global load balancing diagram

Global Server Load Balancing without using DNS

Cloud Leverage's Global Load Balancing functionality extends load balancing to a global geographic scale without using the typical DNS proxy method.  It adds another layer of High Availability and performance to applications by routing traffic using our global IP Anycast Network. Load Balancing technology that relies on DNS for GEO location and routing are inferior and unpredictable due to outdated databases and DNS cache problems that result in alienating clients with outdated DNS cache. By using a non-DNS method of load balancing, the Cloud Leverage customer regains complete control.

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