Measurement Discovery

OpenTestPoint discovery requests allow for the dynamic discovery of the measurements available from nodes running otestpointd. The Controller running as part of otestpointd listens for discovery requests on the endpoint specified as part of the application configuration XML.

A discovery request is issued using a ZeroMQ REQ socket and the DiscoveryRequest message shown below:

package OpenTestPoint;

option optimize_for = SPEED;

message DiscoveryRequest
{
  enum Type
  {
    TYPE_DISCOVERY = 1;
  }
  
  required Type type = 1;
}

message DiscoveryResponse
{
  message Error
  {
    required string what = 1;
  }
  
  message Discovery
  {
    required string publish = 1;
    repeated string names = 2;
  }

  enum Type
  {
    TYPE_ERROR = 1;
    TYPE_DISCOVERY = 2;
  }

  required Type type = 1;
  optional Discovery discovery = 2;
  optional Error error = 3;
}

DiscoveryResponse messages are subdivided into one of two types: DISCOVERY and ERROR.

DiscoveryResponse messages with type set to TYPE_DISCOVERY will have a Discovery message present in the response discovery member.

The Discovery message has the following fields:

Field	Description
publish	The ZeroMQ PUB socket endpoint used for publishing probe reports
names	The total listing of all the names of the probes published by the probe being managed.

DiscoveryResponse messages with type set to TYPE_ERROR will have an Error message present in the response error member.

The Error message has the following field:

Field	Description
description	The description of the error.

The otestpoint-discover application can be used to issue a DiscoveryRequest message. Each probe registers the names of the measurement messages they are capable of publishing when initially loaded by the Controller. Each probe message name is appended with the id specified as part of the application configuration XML.

The below listing shows the output from using otestpoint-discover to query an otestpointd instance. More information on otestpoint-discover can be found using the --help option.

[me@host 1]$ otestpoint-discover node-1:8881
tcp://10.99.0.1:8882
EMANE.RFPipe.Counters.General.node-1
EMANE.RFPipe.Tables.Events.node-1
EMANE.RFPipe.Tables.Neighbor.node-1
EMANE.RFPipe.Tables.Status.node-1
EMANE.VirtualTransport.Counters.General.node-1
EMANE.VirtualTransport.Tables.Events.node-1
EMANE.VirtualTransport.Tables.Status.node-1

Although not required by the framework, it is a best practice for the id value to be directly mapable to the node running the respective otestpointd instance. Using the node hostname works well.