StreamNode

Warning! This page documents an old version of Kapacitor, which is no longer actively developed. Kapacitor v1.2 is the most recent stable version of Kapacitor.

A StreamNode represents the source of data being streamed to Kapacitor via any of its inputs. The stream node allows you to select which portion of the stream you want to process. The stream variable in stream tasks is an instance of a StreamNode.

Example:

    stream
        .from()
           .database('mydb')
           .retentionPolicy('myrp')
           .measurement('mymeasurement')
           .where(lambda: "host" =~ /logger\d+/)
        .window()
        ...

The above example selects only data points from the database mydb and retention policy myrp and measurement mymeasurement where the tag host matches the regex logger\d+

Properties

Property methods modify state on the calling node. They do not add another node to the pipeline, and always return a reference to the calling node.

Database

The database name. If empty any database will be used.

node.database(value string)

Measurement

The measurement name If empty any measurement will be used.

node.measurement(value string)

RetentionPolicy

The retention policy name If empty any retention policy will be used.

node.retentionPolicy(value string)

Truncate

Optional duration for truncating timestamps. Helpful to ensure data points land on specfic boundaries Example:

    stream
       .from().measurement('mydata')
           .truncate(1s)

All incoming data will be truncated to 1 second resolution.

node.truncate(value time.Duration)

Where

Filter the current stream using the given expression. This expression is a Kapacitor expression. Kapacitor expressions are a superset of InfluxQL WHERE expressions. See the Expression docs for more information.

If empty then all data points are considered to match.

node.where(expression tick.Node)

Chaining Methods

Chaining methods create a new node in the pipeline as a child of the calling node. They do not modify the calling node.

Alert

Create an alert node, which can trigger alerts.

node.alert()

Returns: AlertNode

Derivative

Create a new node that computes the derivative of adjacent points.

node.derivative(field string)

Returns: DerivativeNode

Eval

Create an eval node that will evaluate the given transformation function to each data point. A list of expressions may be provided and will be evaluated in the order they are given and results of previous expressions are made available to later expressions.

node.eval(expressions ...tick.Node)

Returns: EvalNode

From

Creates a new stream node that can be further filtered using the Database, RetentionPolicy, Measurement and Where properties. From can be called multiple times to create multiple independent forks of the data stream.

Example:

    // Select the 'cpu' measurement from just the database 'mydb'
    // and retention policy 'myrp'.
    var cpu = stream.from()
                       .database('mydb')
                       .retentionPolicy('myrp')
                       .measurement('cpu')
    // Select the 'load' measurement from any database and retention policy.
    var load = stream.from()
                        .measurement('load')
    // Join cpu and load streams and do further processing.
    cpu.join(load)
            .as('cpu', 'load')
        ...
node.from()

Returns: StreamNode

GroupBy

Group the data by a set of tags.

Can pass literal * to group by all dimensions. Example:

    .groupBy(*)
node.groupBy(tag ...interface{})

Returns: StreamNode

HttpOut

Create an http output node that caches the most recent data it has received. The cached data is available at the given endpoint. The endpoint is the relative path from the API endpoint of the running task. For example if the task endpoint is at "/api/v1/task/<task_name>" and endpoint is "top10", then the data can be requested from "/api/v1/task/<task_name>/top10".

node.httpOut(endpoint string)

Returns: HTTPOutNode

InfluxDBOut

Create an influxdb output node that will store the incoming data into InfluxDB.

node.influxDBOut()

Returns: InfluxDBOutNode

Join

Join this node with other nodes. The data is joined on timestamp.

node.join(others ...Node)

Returns: JoinNode

MapReduce

Perform a map-reduce operation on the data. The built-in functions under influxql provide the selection,aggregation, and transformation functions from the InfluxQL language.

MapReduce may be applied to either a batch or a stream edge. In the case of a batch each batch is passed to the mapper idependently. In the case of a stream all incoming data points that have the exact same time are combined into a batch and sent to the mapper.

node.mapReduce(mr MapReduceInfo)

Returns: ReduceNode

Sample

Create a new node that samples the incoming points or batches.

One point will be emitted every count or duration specified.

node.sample(rate interface{})

Returns: SampleNode

Union

Perform the union of this node and all other given nodes.

node.union(node ...Node)

Returns: UnionNode

Window

Create a new node that windows the stream by time.

NOTE: Window can only be applied to stream edges.

node.window()

Returns: WindowNode