JMS Channels

Contents

Placement in NetarchiveSuite software

Every channel is named after the set of application instances that are expected to receive messages sent to it. All channel names are constructed privately in the dk.netarkivet.common.distribute.ChannelID class. To get a channel, you must use one of the public methods in the  dk.netarkivet.common.distribute.Channels class.

Channel Behavior

There are two types of channels used in the JMS protocol:

• Queue where only one listener takes a message from the channel. For example a queue where a 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.

In NetarchiveSuite we use a naming convention that topic channel names include the string "_ALL_" and the suffix "_TOPIC".

Naming Conventions

The structure of channel names is as follows:

<Environment Name>_<ReplicaID>_[<Channel Specifier Prefix>_]<Channel Specifier>[_<Machine>][_<Application Instance>][_TOPIC]

• 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 of developer running personal environment for e.g. sanity tests. It is read from the setting settings.common.environmentName of the NetarchiveSuite installation.

• ReplicaID Name of the replica (ie the "location" in a distributed system), or COMMON if channel shared by all replicas.

• Channel Specifier Prefix if present is one of the following:
  
  • 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
• Channel Specifier simply expresses what the channel is used for. By convention this (usually) describes what kind of application should listen on this channel.

Here is a complete list of the channels in an actual realistic distributed NAS system (IP addresses have been anonymised for security reasons).