Layer 7 load balancing takes its name from the OSI model, indicating that the load balancer distributes requests to back-end pools based on layer 7 (application) data. While layer 7 load balancing in general can theoretically be done for any well-defined layer 7 application interface, for the purposes of Octavia, L7 functionality refers only to the HTTP protocol and its semantics. Octavia accomplish the logic of layer 7 load balancing through the use of L7 Rules and L7 Policies. An L7 Rule is a single, simple logical test which evaluates to true or false. An L7 Policy is a collection of L7 rules, as well as a defined action that should be taken if all the rules associated with the policy match.
OSI Model (Open Systems Interconnection Model) is a conceptual framework used to describe the functions of a networking system. The OSI model characterizes computing functions into a universal set of rules and requirements in order to support interoperability between different products and software. In the OSI reference model, the communications between a computing system are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. |
An L7 Rule is a single, simple logical test which returns either true or false. It consists of a rule type, a comparison type, a value, and an optional key that gets used depending on the rule type. An L7 rule must always be associated with an L7 policy.
An L7 Policy is a collection of L7 rules associated with a Listener, and which may also have an association to a back-end pool. Policies describe actions that should be taken by the load balancing software if all of the rules in the policy return true.