Definition of Services¶

A service is a set of information that can be discovered by using a unique identifier (the service name). There are two types of services, depending on the way that they were published: dynamic services, those created by a program in execution and static services, created using service files. The services behave similarly without regard of the publication method, however, dynamic services are unpublished automatically when Polo is stopped or restarted (but not when it is reloaded) while static services last as long as the file exists.

Static services¶

All files in the $(MARCOPOLO_DIR)/polo/services or $HOME/.polo/services are considered services, and are expected to have the following structure skeleton (defined in $(MARCOPOLO_DIR)/polo/skel:

{
    "id":"skel",
    "params":{"param1":"value1", "param2":"value2"},
    "groups":["224.0.1.130", "224.0.1.131"],
    "disabled": true
}

– The id parameter can be any string from 1 to 30 characters long if the service is a root service. In the case of user services, the rule still applies, but the final service identifier will be $USER:id.

– The params is an JSON object of custom parameters, useful for filtering, information about the service, etc. The values of each parameter can only be basic types (no nested arrays/objects are allowed). It is an optional parameter.

– The groups parameter is optional and specifies the groups where the service has to be published. If not supplied, the service will be published in all the multicast groups configured for the Polo instance. The parameter must be an array of IP strings. Note that only those groups where Polo is configured to work are valid, and the service will not be published in any other multicast group configured in the service file.

– The disabled parameter is optional, and if defined and set to true will disable the service publication in all groups. Otherwise it will be ignored.

Dynamic services¶

The dynamic services are indistinguishable in behaviour to static services (they can even be created as static services), and are configured using the following tools:

The bindings of Polo during execution time.
The script poloservice offers an interactive method to create a service file and publish it (it uses the Polo binding underneath).