Topics Map > Networking

SLB, Server Load Balancing

For IT Pros: This page contains information about the Server Load Balancing (SLB) service, how to request SLB service, and how to use the SLB service. Most of this information is for IT professionals; end users will connect to the services using the SLB by the hostname the service advertises.

What is Server Load Balancing (SLB)?

Server Load Balancing (SLB) is using a device to sit between the customers and multiple instances of your hardware (called real servers in SLB-speak) used by a service. The SLB device presents a single, virtual server front-end to the customers of the service while spreading the actual traffic out to the real servers so that they each take a part of the load. This allows you to give your customers a single name or IP address for your service, even if you have multiple servers. Your customers connect to the Virtual Server IP address that is configured in the load balancer (VIP in SLB-speak), and the load balancer uses the real servers' load and health check information to decide where each user’s connection will go.

For example, if your customers know your service by the name www.test.illinois.edu, and their traffic needs to be balanced to the 3 web servers on the right, your server load balancing configuration might look like this:

Server Load Balancing

Where can I get SLB?

SLB is available through the DCL Data Center and the Technology Services portion of the data center in RRB in Chicago.

What do I need to know to request SLB services?

  • How much traffic flows to your real servers?
    If your servers have a lot of traffic that isn’t customer facing, we may need to set up a back-end network for that traffic so that it doesn’t flow through the load balancing hardware.
  • What are the names of your real servers?
    You'll need the full hostname for each of your real servers.
  • What data center are your real servers in?
  • What network are your real servers on?
    You'll need to specify the network your real servers are on (if they're not on their own network, you have to get a service-specific network for them before you can request SLB services).
  • What ports (protocols) does your service run on?
    HTTP is port 80, HTTPS is port 443, SMTP is port 25, etc.
  • How many Virtual IPs will you need?
    You will want to use as few as will work, and you will need to know what you wish to name each of them.
  • What firewall group will each VIP need to be in?
  • Who will make changes to the service’s real and virtual servers?
    In SLB-speak, this is a manager.
  • Who needs to be able to take real and virtual servers off line (but not change them)?
    In SLB-speak, this is an operator.
  • What health checks does your service need and how often do you need check it?
    Put this under Additional Info on the request form (or do it yourself in the SLB web interface)
  • SLB web interface basics:
    Do you know how to make a real server and add it to your virtual server? Networking will help you set up your real and virtual servers, but if you need to make adds or changes in the future, it’s usually easiest if you can do them yourself.

How do I start using SLB?

If you've never used SLBs before, you should setup a meeting with the SLB service manager and make sure you have all the information you need to get started.

Once you have all your data together, fill out this form: https://datacenter.cites.illinois.edu/dcs/slbr.form.