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Remote topic views

Consider whether to use remote topic views to share topic data between servers that are not part of the same cluster.

Remote topic views are an extension of topic views. A topic view maps one part of the topic tree to another part. Usually this takes place within a server, but a remote topic view can map topics from a remote server.

Why use a remote topic view?

A remote topic view is useful if you need to make the same data available on multiple servers where clustering is not suitable. This might be for geographical reasons to minimise latency, or because the servers are separated by a firewall.

You can also use the other topic view transformations to process topic data from the remote server and create derived topics (for example, transforming topic values and tree structure or delaying or throttling updates).

How remote topic views work

Like any topic view, a remote topic view creates reference topics based on a set of source topics.

A remote topic view is configured on the server (or cluster) that will receive the reference topics, derived from source topics on the remote server.

The remote topic view is defined with a topic view specification and a remote server definition, both of which can be created with a client API. See Creating a remote server definition for details.

Automatic topic removal with remote topic views

Automatic topic removal can monitor subscriptions to a reference topic created from a normal topic on a remote server with a topic view.

However, subscriptions cannot be monitored if a reference topic is created from a reference topic. For example, suppose a normal topic view is used to create a reference topic on a remote server. If a remote topic view is used to replicate that reference topic, subscriptions to the resulting reference topic will not be counted for automatic removal purposes.

If you want to combine automatic topic removal and remote topic views, avoid using topic views on the remote server to create any topics that could be selected by the remote topic view.

Routing topic limitation

Remote topic views have a limitation when using the deprecated routing topic type.

A routing topic will only resolve to a reference topic if the routing handler at the remote server resolves a value for the remote server client.

Creating a remote topic view

For details of how to create a remote topic view, see ../../data/topictree/topic_views.html#concept_topicviews__remoteview.