StreamNode

A StreamNode represents the source of data being streamed to Kapacitor via any of its inputs. The stream variable in stream tasks is an instance of a StreamNode. StreamNode.From is the method/property of this node.

Index

Properties

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. Chaining methods are marked using the | operator.

Deadman

Helper function for creating an alert on low throughput, a.k.a. deadman's switch.

Threshold – trigger alert if throughput drops below threshold in points/interval.
Interval – how often to check the throughput.
Expressions – optional list of expressions to also evaluate. Useful for time of day alerting.

Example:

    var data = stream
        |from()...
    // Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
    data
        |deadman(100.0, 10s)
    //Do normal processing of data
    data...

The above is equivalent to this Example:

    var data = stream
        |from()...
    // Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
    data
        |stats(10s)
            .align()
        |derivative('emitted')
            .unit(10s)
            .nonNegative()
        |alert()
            .id('node \'stream0\' in task \'{{ .TaskName }}\'')
            .message('{{ .ID }} is {{ if eq .Level "OK" }}alive{{ else }}dead{{ end }}: {{ index .Fields "emitted" | printf "%0.3f" }} points/10s.')
            .crit(lambda: "emitted" <= 100.0)
    //Do normal processing of data
    data...

The id and message alert properties can be configured globally via the 'deadman' configuration section.

Since the AlertNode is the last piece it can be further modified as usual. Example:

    var data = stream
        |from()...
    // Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
    data
        |deadman(100.0, 10s)
            .slack()
            .channel('#dead_tasks')
    //Do normal processing of data
    data...

You can specify additional lambda expressions to further constrain when the deadman's switch is triggered. Example:

    var data = stream
        |from()...
    // Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
    // Only trigger the alert if the time of day is between 8am-5pm.
    data
        |deadman(100.0, 10s, lambda: hour("time") >= 8 AND hour("time") <= 17)
    //Do normal processing of data
    data...

node|deadman(threshold float64, interval time.Duration, expr ...ast.LambdaNode)

Returns: AlertNode

From

Creates a new FromNode 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: FromNode

Stats

Create a new stream of data that contains the internal statistics of the node. The interval represents how often to emit the statistics based on real time. This means the interval time is independent of the times of the data points the source node is receiving.

node|stats(interval time.Duration)

Returns: StatsNode