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IceLocatorDiscovery

IceLocatorDiscovery Overview

IceLocatorDiscovery is an Ice plug-in that discovers IceGrid and custom locators on a network using UDP multicast. Once installed, the plug-in automatically and transparently issues a multicast query in an attempt to find one or more locators, collects the responses, and configures the Ice runtime accordingly. The primary advantage of using IceLocatorDiscovery is that it eliminates the need to manually configure and maintain the Ice.Default.Locator property. It's even more helpful in a replicated IceGrid deployment consisting of a master replica and one or more slave replicas, where the Ice.Default.Locator property would normally include endpoints for some or all of the replicas. Avoiding the need to configure the locator endpoints relieves some of the administrative burden, simplifies deployment and configuration tasks, and adds more flexibility to your application designs.

You can think of IceLocatorDiscovery as an application-specific version of IceDiscovery geared primarily toward IceGrid users.

Installing IceLocatorDiscovery

The IceLocatorDiscovery plug-in must be installed in every client that needs to locate objects; you can optionally install it in IceGrid nodes and registry replicas.

When you write a client, you should install IceLocatorDiscovery in your communicator using the pluginFactories field of InitializationData:

CPP 
#include <IceLocatorDiscovery/IceLocatorDiscovery.h>

Ice::InitializationData initData;
initData.properties = Ice::createProperties(argc, argv);
initData.pluginFactories = {IceLocatorDiscovery::locatorDiscoveryPluginFactory()};

Ice::CommunicatorPtr communicator = Ice::initialize(initData);

Alternatively, you can install the IceLocatorDiscovery plug-in at runtime using configuration:

CODE 
Ice.Plugin.IceLocatorDiscovery=IceLocatorDiscovery:createIceLocatorDiscovery

Configuring IceLocatorDiscovery

Applications configure the IceLocatorDiscovery plug-in using configuration properties; the plug-in does not provide a local API.

IceLocatorDiscovery Property Overview

The IceDiscovery plug-in supports a number of configuration properties, many of which affect the endpoints that the plug-in uses for its queries:

  • Lookup endpoint
    This is the multicast endpoint on which all lookup queries are broadcast. It must use an IPv4 or IPv6 address in the multicast range with a fixed port.

  • Reply endpoint
    This is the endpoint on which the plug-in receives replies from locators (an IceGrid registry is the most common example of a locator). In general, this endpoint should not use a fixed port.

The plug-in uses sensible default values for all of its configuration properties, such that it's often unnecessary to define any of the plug-in's properties. However, it's still important to understand how the plug-in derives its endpoint information.

First, you can override the default endpoint that the plug-in uses to broadcast its queries by defining IceLocatorDiscovery.Lookup, otherwise the plug-in computes this endpoint as follows:

IceLocatorDiscovery.Lookup=udp -h address -p port [--interface interface]

where

For IceGrid users, the lookup endpoint must use the same multicast address and port as IceGrid.Registry.Discovery.Endpoints in the registry configuration.

IceLocatorDiscovery also creates object adapters in each communicator in which it's installed, including the object adapter IceLocatorDiscovery.Reply. This object adapter corresponds to the Reply endpoint mentioned above.

As you can see, the properties IceLocatorDiscovery.Address, IceLocatorDiscovery.Port and IceLocatorDiscovery.Interface are simply used as convenient shortcuts for customizing the details of the plug-in's endpoints. For example, suppose we want to use a different multicast address and port:

CODE 
IceLocatorDiscovery.Address=239.255.0.99
IceLocatorDiscovery.Port=8000

The plug-in derives the following property from these settings:

CODE 
IceLocatorDiscovery.Lookup=udp -h 239.255.0.99 -p 8000

All of the components of an IceGrid application must use the same multicast address and port. You should also consider defining IceLocatorDiscovery.InstanceName to avoid any potential collisions from unrelated IceGrid applications that happen to use the same address and port.

Configuring IceLocatorDiscovery in User Applications

For a client application, remove any existing definition of Ice.Default.Locator, then install the plug-in and optionally configuring its addressing information.

For a server deployed with IceGrid, you normally don't need to install the IceLocatorDiscovery plug-in.

Configuring IceLocatorDiscovery in IceGrid Administrative Clients

Support for multicast discovery is built into the command-line and graphical IceGrid administrative utilities, therefore you don't need to install the plug-in. Both utilities support configuration properties similar to the ones we described above for defining the multicast address and port.

Configuring IceLocatorDiscovery in an IceGrid Registry

An IceGrid registry does not need the plug-in if it's the master replica or the only registry in a deployment, although there's no harm in installing it. The plug-in is useful for slave replicas because it allows them to locate the current master without configuring the master's endpoints. Install and configure the plug-in for slave replicas just like you would for any C++ client.

IceGrid registries listen for multicast discovery queries by default, but you can disable this feature by setting IceGrid.Registry.Discovery.Enabled to 0.

If you've changed the default multicast address or port for IceLocatorDiscovery, you must also make corresponding changes to the configuration of each registry. The registry supports properties similar to those of IceLocatorDiscovery:

These properties influence the endpoint on which the registry listens for multicast discovery queries. If you don't override the endpoint by setting IceGrid.Registry.Discovery.Endpoints, the registry uses these properties to compute its endpoint as follows:

IceGrid.Registry.Discovery.Endpoints=udp -h address -p port [--interface interface]

You don't need to define any IceGrid.Registry.Discovery.* properties if you want the registry to listen for discovery queries on its default multicast address and port.

Configuring IceLocatorDiscovery in an IceGrid Node

The plug-in is useful for IceGrid nodes because it allows them to locate the registry without configuring the registry's endpoints. Install and configure the plug-in in a node just like you would for any C++ client.

See Also

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