Slobrok is an acronym for Service Location Broker,
and it is a name service used in Vespa.
The service listens on a specific port -
to find the
Slobrok service's port number.
Slobrok is running by default on the administration node as well as one or two other random nodes for redundancy. Best practise for a multi-node, high-availability application is found in the multinode-HA sample application. In this application, slobrok instances are hosted on nodes running config servers. The motivation is, like the config servers, Vespa requires slobrok to be up for services to function. Operating slobrok is the same as config servers, too - three is enough for most applications. As slobrok requires minimal system resources, it does not impact other services running on the same node -> using config server nodes is ideal.
Clients, like the Document API, will do lookups on any of the service location broker nodes. Slobrok is not used in the query pipeline. The cluster-controller uses slobrok to evaluate service availability.
The Slobrok process looks like: