Coral Actors

Coral actor types

The following Coral Actors for stream transformations are defined:

name	class	description
cassandra	CassandraActor	connect to a Cassandra datasource
fsm	FsmActor	select a state according to key
generator	GeneratorActor	generate data based on a JSON template and distribution definitions
group	GroupByActor	partition the stream
httpbroadcast	HttpBroadcastActor	pass (HTTP supplied) JSON to other actors
httpclient	HttpClientActor	post to a service URL
json	JsonActor	transform an input JSON
kafka-consumer	KafkaConsumerActor	reads data from Kafka
kafka-producer	KafkaProducerActor	writes data to Kafka
log	LogActor	logs data to a file
linearregression	LinearRegressionActor	performs prediction on streaming data
lookup	LookupActor	find data for a key value
sample	SampleActor	emits only a fraction of the supplied trigger JSON
stats	StatsActor	accumulate some basic statistics
threshold	ThresholdActor	emit only when a specified field value exceeds a threshold
window	WindowActor	collect input objects and emit only when reaching a certain number or a certain time
zscore	ZscoreActor	determine if a value is an outlier according to the Z-score statistic

Creating a Coral actor

The JSON to create a Coral Actor conforms to JSON API. The attributes in the JSON to create a Coral Actor contain the following fields:

field	type	required	description
type	string	yes	the name of the actor
params	json	yes	depends on the actor
timeout	json	no	timeout JSON
group	json	no	group by JSON

The timeout JSON is defined as follows:

field	type	required	description
mode	string	yes	“continue” for continuing timer events; “exit” for act-once timer behavior
duration	number	yes	the duration of the timer in seconds

The timeout definition will determine how the timer function of an actor (if defined) is triggered.

The group by JSON is defined with a single field:

field	type	required	description
by	string	yes	the value is the name of a field in the stream JSON

Having a group by field defined will invoke the (GroupByActor)[/coral/docs/Actors-groupActor] to partition the stream and control the creation of underlying actors for each partition.

Example

Create the statistics actor with a timer action every 60 seconds. Group the statistics by the value of the trigger-field tag.

Note: the data, attributes and "type": "actors" are used because of the conformation to JSON API.

Setting the trigger

After defining an actor, you can connect it to another actor by setting the trigger and/or collect.

Example

Using your own Coral actors

When the provided Coral actors or a combination of them don’t provide the functionality you need, you can write your own Coral actor and use it. To use your own Coral actor, you need to create a factory that extends the ActorPropFactory trait. See for an example the DefaultActorPropFactory, which contains all the provided Coral actors.

Next, you create a jar with your Coral actor(s) and your factory and add this jar to the classpath. To configure the Coral platform to use your factory, add the following to the application.conf:

You can define more than one factory. When looking for a Coral actor by name, the search order is the order in which the factories are given. Before searching in user defined factories, the default factory with the provided Coral actors is searched for a given Coral actor name, so it is not possible to redefine one of the provided actors.