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// -*- C++ -*-
// $Id$
// ============================================================================
//
// = LIBRARY
// TAO_LoadBalancing
//
// = FILENAME
// LoadBalancing.idl
//
// = AUTHOR
// Ossama Othman <ossama@uci.edu>
//
// ============================================================================
#ifndef TAO_LOADBALANCING_IDL
#define TAO_LOADBALANCING_IDL
module LoadBalancing
{
// = TITLE
// This module defines the interfaces and data types used in TAO's
// Load Balancing service.
// = DESCRIPTION
// TAO's Load Balancer manages distribution of requests to
// replicas of a given Object in an effort to ensure that the
// applications/hosts pointed to by the Object reference are as
// equally loaded as possible, i.e. load balanced.
// The definition of 'load' is application specific, for
// example, some applications may choose to load balance access
// to multiple dedicated lines, or separate network interfaces,
// as well as more traditional load balancing metrics, such as
// CPU or disk load.
interface ReplicaControl
{
// = TITLE
// An interface that specifies methods the Load Balancer
// invokes when informing the ReplicaControl of the
// underlying Object's load status.
// = DESCRIPTION
// The ReplicaControl provides a means to control the load on
// the Object it is controlling without forcing existing
// Objects to change their interface. The LoadBalancer
// issues advisories to the ReplicaControl when it detects
// load levels that should be handled in a certain way.
void high_load_advisory ();
// When the LoadBalancer detects a "high" load on a given Object
// via its ReplicaProxy, it issues a high load advisory to the
// ReplicaControl by invoking this method; typically causing the
// underlying object to stop accepting requests.
void nominal_load_advisory ();
// If a "nominal" load is detected, then a nominal load advisory
// is issued, typically causing the Object to once again accept
// requests.
};
interface ReplicaProxy
{
// = TITLE
// This interface provides the methods that the
// ReplicaControl object invokes.
// = DESCRIPTION
// The ReplicaProxy resides in the LoadBalancer.
// A ReplicaControl object obtains a reference to a
// ReplicaProxy from the LoadBalancer, and invokes the
// methods in the interface to send load information to the
// Load Balancer.
exception InvalidLoad
{
// = TITLE
// An invalid load was sent to the ReplicaProxy.
};
exception NilControl
{
// = TITLE
// This exception indicates that a nil ReplicaControl
// reference was passed to the ReplicaProxy.
};
exception NilReplica
{
// = TITLE
// This exception indicates that the reference to the
// object being load balanced was nil.
};
exception NotConnected
{
// = TITLE
// This exception is thrown when an attempt is made to
// disconnect from the LoadBalancer but no connection is
// currently established.
};
oneway void current_load (in float load);
// Send current load to the Load Balancer.
// The application must ensure that all replicas use the same
// notion of load.
void disconnect () raises (NotConnected);
// Disconnect the ReplicaControl from the Load Balancer. The
// Object that the ReplicaControl controls will be no longer be
// load balanced.
};
interface LoadBalancer
{
// = TITLE
// The LoadBalancer interface.
// = DESCRIPTION
// The LoadBalancer distributes incoming requests for a given
// Object among several replicas of that Object, thus helping
// to ensure that loads are as well balanced across the
// systems the replicas are running on as possible.
exception InvalidReplicaProxy
{
// = TITLE
// This exception indicates that an attempt was made to
// use a ReplicaProxy that is not registered with the
// LoadBalancer.
};
ReplicaProxy connect (in ReplicaControl control,
in Object replica)
raises (ReplicaProxy::NilControl,
ReplicaProxy::NilReplica);
// Register ReplicaControl with LoadBalancer, thus allowing the
// Object to be load balanced.
Object group_identity ();
// Return the reference to the object that represents the
// Replica group being load balanced. This "group identity"
// object will cause the client to redirect its requests to a
// Replica that fits a specific load balancing criteria.
};
// @@ Ossama: we may want to add interfaces or operations to access
// the current list of loads, that would be useful for monitoring
// applications, and nice GUI-based demos.
// @@ Ossama: another idea: we have been using this stuff to make
// all the loads equal, but what if the objective is to keep the
// load below some value? Maybe we should provide some callback
// mechanism to let the application know: the load is too high and
// there is nothing i can do about it, add more CPUS or reduce the
// load!
// Such feedback would be very useful for some applications.
};
#endif /* TAO_LOADBALANCER_IDL */
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