Tagging

Note

This feature is only available in Axon Server Enterprise and compatible with version 4.2 onwards of Axon.

To optimise the connections between framework clients and Axon Server, it is possible to tag both clients and Axon Server with information which describes properties of those clients and nodes. Axon Server will then use these tags to make a connection to the client.

A typical tag could describe where the respective client and server node are running (e.g. a cloud provider's region) encouraging that the nearest, and therefore fastest, connections are made.

Tag Matching

A match is made when the the label and the value of the tag matches. For example, a server tagged with computeRegion=europe will match with a client tag of computeRegion=europe. Similarly if a server is tagged with computeRegion=europe and client is tagged with computeRegion=asia then this is not considered a match.

If both client and server are tagged with multiple tags then the connection that is made will be based on the highest number of matches. If multiple nodes have a equal number of matching tags then the node with the lightest load is chosen.

If no matching tags are available at all, it will connect to any available node.

Enabling tagging

To enable tagging you must configure both the client and server.

Axon Server

You can configure the tags that you would like for each node through properties using axoniq.axonserver.tags.computeRegion=europe. Additional tags can be specified by adding to the tags element (e.g. axoniq.axonserver.tags.networkSpeed=fast).

Client

On the client side, there are two approaches through which you can specify tags. Either the properties file is expanded (similar to server configuration, also allowing additional tags to be added) in a Spring Boot environment, or a TagsConfiguration object is registered to the Configurer.

Axon Configuration API

Map<String, String> tags = new HashMap();
// Insert tags
DefaultConfigurer.defaultConfiguration()
    .configureTags(config -> new TagsConfiguration(tags));

Spring Boot AutoConfiguration

axon.tags.computeRegion=europe