## page was renamed from Developer Manual 3.14/Channels
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== JMS Channels ==
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=== Placement in NetarchiveSuite software ===
Every channel is named after the set of applications instances that are expected to receive messages sent to it. All channel names are constructed privately in the ~+{{{dk.netarkivet.distribute.ChannelID}}}+~ class. To get a channel, you must use one of the public methods in ~+{{{dk.netarkivet.distribute.Channels}}}+~.

=== Channel Behavior ===
There are used to types of channels:

 * '''''Queue''''' where only one listener takes a message from the queue. For example a queue where request for doing a harvest is only received by one harvester.
 * '''''Topic''''' where all listeners takes a copy of the message. For example a batch job which has to be executed by all bitarchive applications.
The type of channel is not affecting the channel name directly. It is indicated by the Channel Prefix, since only channel names starting with ~+{{{ALL}}}+~ are topics, while the rest are queues.

The channel type for different queues is given in a table in the next section.

=== Naming Conventions ===
The structure of channel names are as follows:

<Environment Name>_<Channel Prefix>_<Replica Annotation>[_<Machine>][_<Application Instance>]

 * '''Environment Name''' value must be the same for all channels on all JVMs belonging to a single !NetarchiveSuite installation. It identifies the environment for the queue, e.g.: "DEV", "TEST", "RELEASETEST", "CLOVER", "PROD" or initials on developer running personal environment for e.g. sanity tests. It is read from the setting ~+{{{settings.common.environmentName}}}+~ of the !NetarchiveSuite installation.
 * '''''Channel Prefix''''''''''' is constructed by a convention for channel behavior together with denotation of the concerned application(s). For example '''THE_SCHED''' uses the convention '''THE''' for '''SCHED''' denoting the scheduler of the harvester.
 . The conventions for channel behavior are:
  * '''THE''' - communicate with singleton in the system.
  * '''THIS''' - communicate with one uniquely identified instance of a number of distributed listeners.
  * '''ANY''' - has all instances listening to the same queue.
  * '''ALL''' - is used for topics only, i.e. topics are sent to ''all'' listeners on the channel.
 * '''''Use Replica Id''''''''''' will result in a channel name with the replica identifier in question (which must match possible replicas in settings). In case of no use of replica id the '''COMMON''' will be used.
 * '''''Use IP Node''''' will result in a channel name with the IP address of the machine whether the application in question is placed. It is read directly from the running system.
 . In case of no use of IP Node, nothing will be written.
 * '''''Use Application Instance Id''''' is used, if only one process is expected to listen to the queue. It will result in a channel name with an identification of the individual application instance. It consists of the application abbreviation (uppercase letters of application name) and the application instance identifier from the settings. It is read from the common settings:  ~+{{{settings.common.applicationName}}}+~ and ~+{{{settings.common.applicationInstanceId}}}+~.
 . In case of no use of Application Instance Id, nothing will be written.
 * '''''Channel Type''''' is only here to complete the picture. Please refer to the section on channel behavior.
Channel names are constructed as described in the below table (columns described after the table).
||'''''Channel Prefix''''''''''' ||'''''Use Replica Id''''' <<BR>> ''(for Replica Annotation)'' ||'''''Use IP Node''''' <<BR>> ''(for Machine)'' ||'''''Use Application Instance Identification''''''''''' || '''''Channel Type''''''''''' || '''''Example''''' ||
||THE_SCHED || No ||No ||No ||Queue || PROD_THE_SCHED_COMMON ||
||ANY_HIGHPRIORITY_HACO ||No ||No ||No ||Queue || PROD_ANY_HIGHPRIORITY_HACO_COMMON ||
||ANY_LOWPRIORITY_HACO ||No ||No ||No ||Queue || PROD_ANY_LOWPRIORITY_HACO_COMMON ||
||THIS_REPOS_CLIENT ||No ||Yes ||Yes ||Queue || PROD_THIS_REPOS_CLIENT_COMMON_130_226_258_7_HCA_HIGH ||
||THE_REPOS || No ||No ||No ||Queue || PROD_THE_REPOS_COMMON ||
||THE_BAMON || Yes ||No ||No ||Queue || PROD_THE_BAMON_TWO ||
||ALL_BA || Yes ||No ||No ||Topic || PROD_ALL_BA_TWO ||
||ANY_BA || Yes ||No ||No ||Queue || PROD_ANY_BA_TWO ||
||THIS_INDEX_CLIENT ||No ||Yes ||Yes ||Queue || PROD_THIS_INDEX_CLIENT_COMMON_130_226_258_7_ISA ||
||INDEX_SERVER ||No ||No ||No ||Queue || PROD_INDEX_SERVER_COMMON ||
||MONITOR ||No ||No ||No ||Queue || PROD_MONITOR_COMMON ||
||ERROR ||No ||No ||No ||Queue || PROD_ERROR_COMMON ||
|| THE_CR || Yes || No || No || Queue || PROD_THE_CR_THREE ||


The examples are using values

 * Environment name ~+{{{PROD}}}+~
 * Possible replica identifiers ~+{{{ONE}}}+~ or ~+{{{TWO}}}+~
 * IP on machine ~+{{{130.226.258.7}}}+~
 * Application instances
  * ~+{{{HCA_HIGH}}}+~ (for !HarvestControllerApplication with instance id ~+{{{"HIGH"}}}+~ )
  * ~+{{{ISA}}}+~ (for !IndexServerApplication with instance id ~+{{{""}}}+~ )
=== Design Notes ===
Note that creation of channel names for the ANY xxx_HACO-queues are designed in a way so extension to more priorities is easy.