Octavia Glossary¶
As the Octavia project evolves, it’s important that people working on Octavia, users using Octavia, and operators deploying Octavia use a common set of terminology in order to avoid misunderstandings and confusion. To that end, we are providing the following glossary of terms.
Note also that many of these terms are expanded upon in design documents in this same repository. What follows is a brief but necessarily incomplete description of these terms.
- Amphora
Virtual machine, container, dedicated hardware, appliance or device that actually performs the task of load balancing in the Octavia system. More specifically, an amphora takes requests from clients on the front-end and distributes these to back-end systems. Amphorae communicate with their controllers over the LB Network through a driver interface on the controller.
- Amphora Load Balancer Driver
Component of the controller that does all the communication with amphorae. Drivers communicate with the controller through a generic base class and associated methods, and translate these into control commands appropriate for whatever type of software is running on the back-end amphora corresponding with the driver. This communication happens over the LB network.
- Apolocation
Term used to describe when two or more amphorae are not colocated on the same physical hardware (which is often essential in HA topologies). May also be used to describe two or more loadbalancers which are not colocated on the same amphora.
- Controller
Daemon with access to both the LB Network and OpenStack components which coordinates and manages the overall activity of the Octavia load balancing system. Controllers will usually use an abstracted driver interface (usually a base class) for communicating with various other components in the OpenStack environment in order to facilitate loose coupling with these other components. These are the “brains” of the Octavia system.
- HAProxy
Load balancing software used in the reference implementation for Octavia. (See http://www.haproxy.org/ ). HAProxy processes run on amphorae and actually accomplish the task of delivering the load balancing service.
- Health Monitor
An object that defines a check method for each member of the pool. The health monitor itself is a pure-db object which describes the method the load balancing software on the amphora should use to monitor the health of back-end members of the pool with which the health monitor is associated.
- L7 Policy
- Layer 7 Policy
Collection of L7 rules that get logically ANDed together as well as a routing policy for any given HTTP or terminated HTTPS client requests which match said rules. An L7 Policy is associated with exactly one HTTP or terminated HTTPS listener.
For example, a user could specify an L7 policy that any client request that matches the L7 rule “request URI starts with ‘/api’” should get routed to the “api” pool.
- L7 Rule
- Layer 7 Rule
Single logical expression used to match a condition present in a given HTTP or terminated HTTPS request. L7 rules typically match against a specific header or part of the URI and are used in conjunction with L7 policies to accomplish L7 switching. An L7 rule is associated with exactly one L7 policy.
For example, a user could specify an L7 rule that matches any request URI path that begins with “/api”
- L7 Switching
- Layer 7 Switching
This is a load balancing feature specific to HTTP or terminated HTTPS sessions, in which different client requests are routed to different back-end pools depending on one or more layer 7 policies the user might configure.
For example, using L7 switching, a user could specify that any requests with a URI path that starts with “/api” get routed to the “api” back-end pool, and that all other requests get routed to the default pool.
- LB Network
Load Balancer Network. The network over which the controller(s) and amphorae communicate. The LB network itself will usually be a nova or neutron network to which both the controller and amphorae have access, but is not associated with any one tenant. The LB Network is generally also not part of the undercloud and should not be directly exposed to any OpenStack core components other than the Octavia Controller.
- Listener
Object representing the listening endpoint of a load balanced service. TCP / UDP port, as well as protocol information and other protocol- specific details are attributes of the listener. Notably, though, the IP address is not.
- Load Balancer
Object describing a logical grouping of listeners on one or more VIPs and associated with one or more amphorae. (Our “Loadbalancer” most closely resembles a Virtual IP address in other load balancing implementations.) Whether the load balancer exists on more than one amphora depends on the topology used. The load balancer is also often the root object used in various Octavia APIs.
- Load Balancing
The process of taking client requests on a front-end interface and distributing these to a number of back-end servers according to various rules. Load balancing allows for many servers to participate in delivering some kind TCP or UDP service to clients in an effectively transparent and often highly-available and scalable way (from the client’s perspective).
- Member
Object representing a single back-end server or system that is a part of a pool. A member is associated with only one pool.
- Octavia
Octavia is an operator-grade open source load balancing solution. Also known as the Octavia system or Octavia project. The term by itself should be used to refer to the system as a whole and not any individual component within the Octavia load balancing system.
- Pool
Object representing the grouping of members to which the listener forwards client requests. Note that a pool is associated with only one listener, but a listener might refer to several pools (and switch between them using layer 7 policies).
- TLS Termination
- Transport Layer Security Termination
Type of load balancing protocol where HTTPS sessions are terminated (decrypted) on the amphora as opposed to encrypted packets being forwarded on to back-end servers without being decrypted on the amphora. Also known as SSL termination. The main advantages to this type of load balancing are that the payload can be read and / or manipulated by the amphora, and that the expensive tasks of handling the encryption are off-loaded from the back-end servers. This is particularly useful if layer 7 switching is employed in the same listener configuration.
- VIP
- Virtual IP Address
Single service IP address which is associated with a load balancer. This is similar to what is described here: http://en.wikipedia.org/wiki/Virtual_IP_address In a highly available load balancing topology in Octavia, the VIP might be assigned to several amphorae, and a layer-2 protocol like CARP, VRRP, or HSRP (or something unique to the networking infrastructure) might be used to maintain its availability. In layer-3 (routed) topologies, the VIP address might be assigned to an upstream networking device which routes packets to amphorae, which then load balance requests to back-end members.
