BarrierNode

The barrier node emits a barrier based on one of the following:

• Idle time since the last data point was received
• Periodic timer based on the system time

Barriers let you execute pipelines without data traffic. Data points received after a specified barrier are dropped.

Example barrier based on idle time

stream
  |from()
    .measurement('cpu')
  |barrier()
    .idle(11s) // Must be longer than the window period
    .delete(TRUE)
  |window()
    .period(10s)
    .every(5s)
  |top(10, 'value')
  // Post the top 10 results over the last 10s updated every 5s.
  |httpPost('http://example.com/api/top10')

{{% note %}} In .delete(TRUE), TRUE must be uppercase. {{% /note %}}

Constructor

Property Methods

Chaining Methods

Alert, Barrier, Bottom, ChangeDetect, Combine, Count, CumulativeSum, Deadman, Default, Delete, Derivative, Difference, Distinct, Ec2Autoscale, Elapsed, Eval, First, Flatten, GroupBy, HoltWinters, HoltWintersWithFit, HttpOut, HttpPost, InfluxDBOut, Join, K8sAutoscale, KapacitorLoopback, Last, Log, Max, Mean, Median, Min, Mode, MovingAverage, Percentile, Sample, Shift, Sideload, Spread, StateCount, StateDuration, Stats, Stddev, Sum, SwarmAutoscale, Top, Trickle, Union, Where, Window

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. Property methods are marked using the . operator.

Idle

Emit barrier based on idle time since the last received message. Must be greater than zero and longer than the window period.

barrier.idle(value time.Duration)

{{% warn %}}

Barrier idle time and window period

idle must be greater than period of the associated window. If idle times are less than the window period, data may be lost. {{% /warn %}}

Period

Emit barrier based on periodic timer. The timer is based on system clock rather than message time. Must be greater than zero.

barrier.period(value time.Duration)

Delete

Delete indicates that the group should be deleted after processing each barrier. This includes the barrier node itself, meaning that if delete is true, the barrier is triggered only once for each group and the barrier node forgets about the group. The group will be created again if a new point is received for the group.

This is useful if you have increasing cardinality over time as once a barrier is triggered for a group it is then deleted, freeing any resources managing the group.

barrier.delete()

{{% note %}} delete will free system resources used for managing groups and can help to maintain the overall performance of Kapacitor, but these gains are minimal. For information about optimizing tasks, see How can I optimize Kapacitor tasks? {{% /note %}}

Quiet

Suppress all error logging events from this node.

barrier.quiet()

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.

Alert

Create an alert node, which can trigger alerts.

barrier|alert()

Returns: AlertNode

Barrier

Create a new Barrier node that emits a BarrierMessage periodically.

One BarrierMessage will be emitted every period duration.

barrier|barrier()

Returns: BarrierNode

Bottom

Select the bottom num points for field and sort by any extra tags or fields.

barrier|bottom(num int64, field string, fieldsAndTags ...string)

Returns: InfluxQLNode

ChangeDetect

Create a new node that only emits new points if different from the previous point.

barrier|changeDetect(field string)

Returns: ChangeDetectNode

Combine

Combine this node with itself. The data is combined on timestamp.

barrier|combine(expressions ...ast.LambdaNode)

Returns: CombineNode

Count

Count the number of points.

barrier|count(field string)

Returns: InfluxQLNode

CumulativeSum

Compute a cumulative sum of each point that is received. A point is emitted for every point collected.

barrier|cumulativeSum(field string)

Returns: InfluxQLNode

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...

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

Returns: AlertNode

Default

Create a node that can set defaults for missing tags or fields.

barrier|default()

Returns: DefaultNode

Delete

Create a node that can delete tags or fields.

barrier|delete()

Returns: DeleteNode

Derivative

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

barrier|derivative(field string)

Returns: DerivativeNode

Difference

Compute the difference between points independent of elapsed time.

barrier|difference(field string)

Returns: InfluxQLNode

Distinct

Produce batch of only the distinct points.

barrier|distinct(field string)

Returns: InfluxQLNode

Ec2Autoscale

Create a node that can trigger autoscale events for a ec2 autoscalegroup.

barrier|ec2Autoscale()

Returns: Ec2AutoscaleNode

Elapsed

Compute the elapsed time between points.

barrier|elapsed(field string, unit time.Duration)

Returns: InfluxQLNode

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. The results are available to later expressions.

barrier|eval(expressions ...ast.LambdaNode)

Returns: EvalNode

First

Select the first point.

barrier|first(field string)

Returns: InfluxQLNode

Flatten

Flatten points with similar times into a single point.

barrier|flatten()

Returns: FlattenNode

GroupBy

Group the data by a set of tags.

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

    |groupBy(*)

barrier|groupBy(tag ...interface{})

Returns: GroupByNode

HoltWinters

Compute the Holt-Winters (/influxdb/v1/query_language/functions/#holt-winters) forecast of a data set.

barrier|holtWinters(field string, h int64, m int64, interval time.Duration)

Returns: InfluxQLNode

HoltWintersWithFit

Compute the Holt-Winters (/influxdb/v1/query_language/functions/#holt-winters) forecast of a data set. This method also outputs all the points used to fit the data in addition to the forecasted data.

barrier|holtWintersWithFit(field string, h int64, m int64, interval time.Duration)

Returns: InfluxQLNode

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 /kapacitor/v1/tasks/<task_id> and endpoint is top10, then the data can be requested from /kapacitor/v1/tasks/<task_id>/top10.

barrier|httpOut(endpoint string)

Returns: HTTPOutNode

HttpPost

Creates an HTTP Post node that POSTS received data to the provided HTTP endpoint. HttpPost expects 0 or 1 arguments. If 0 arguments are provided, you must specify an endpoint property method.

barrier|httpPost(url ...string)

Returns: HTTPPostNode

InfluxDBOut

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

barrier|influxDBOut()

Returns: InfluxDBOutNode

Join

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

barrier|join(others ...Node)

Returns: JoinNode

K8sAutoscale

Create a node that can trigger autoscale events for a kubernetes cluster.

barrier|k8sAutoscale()

Returns: K8sAutoscaleNode

KapacitorLoopback

Create an kapacitor loopback node that will send data back into Kapacitor as a stream.

barrier|kapacitorLoopback()

Returns: KapacitorLoopbackNode

Last

Select the last point.

barrier|last(field string)

Returns: InfluxQLNode

Log

Create a node that logs all data it receives.

barrier|log()

Returns: LogNode

Max

Select the maximum point.

barrier|max(field string)

Returns: InfluxQLNode

Mean

Compute the mean of the data.

barrier|mean(field string)

Returns: InfluxQLNode

Median

Compute the median of the data.

Note: This method is not a selector. If you want the median point, use .percentile(field, 50.0).

barrier|median(field string)

Returns: InfluxQLNode

Min

Select the minimum point.

barrier|min(field string)

Returns: InfluxQLNode

Mode

Compute the mode of the data.

barrier|mode(field string)

Returns: InfluxQLNode

MovingAverage

Compute a moving average of the last window points. No points are emitted until the window is full.

barrier|movingAverage(field string, window int64)

Returns: InfluxQLNode

Percentile

Select a point at the given percentile. This is a selector function, no interpolation between points is performed.

barrier|percentile(field string, percentile float64)

Returns: InfluxQLNode

Sample

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

One point will be emitted every count or duration specified.

barrier|sample(rate interface{})

Returns: SampleNode

Shift

Create a new node that shifts the incoming points or batches in time.

barrier|shift(shift time.Duration)

Returns: ShiftNode

Sideload

Create a node that can load data from external sources.

barrier|sideload()

Returns: SideloadNode

Spread

Compute the difference between min and max points.

barrier|spread(field string)

Returns: InfluxQLNode

StateCount

Create a node that tracks number of consecutive points in a given state.

barrier|stateCount(expression ast.LambdaNode)

Returns: StateCountNode

StateDuration

Create a node that tracks duration in a given state.

barrier|stateDuration(expression ast.LambdaNode)

Returns: StateDurationNode

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.

barrier|stats(interval time.Duration)

Returns: StatsNode

Stddev

Compute the standard deviation.

barrier|stddev(field string)

Returns: InfluxQLNode

Sum

Compute the sum of all values.

barrier|sum(field string)

Returns: InfluxQLNode

SwarmAutoscale

Create a node that can trigger autoscale events for a Docker swarm cluster.

barrier|swarmAutoscale()

Returns: SwarmAutoscaleNode

Top

Select the top num points for field and sort by any extra tags or fields.

barrier|top(num int64, field string, fieldsAndTags ...string)

Returns: InfluxQLNode

Trickle

Create a new node that converts batch data to stream data.

barrier|trickle()

Returns: TrickleNode

Union

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

barrier|union(node ...Node)

Returns: UnionNode

Where

Create a new node that filters the data stream by a given expression.

barrier|where(expression ast.LambdaNode)

Returns: WhereNode

Window

Create a new node that windows the stream by time.

NOTE: Window can only be applied to stream edges.

barrier|window()

Returns: WindowNode