--- title: BarrierNode description: BarrierNode emits a barrier with the current time, according to the system clock, and allows pipelines to be forced in the absence of data traffic. The barrier emitted will be based on either idle time since the last received message or on a periodic timer based on the system clock. url: https://docs.influxdata.com/kapacitor/v1/reference/nodes/barrier_node/ estimated_tokens: 12050 product: Kapacitor version: v1 --- # 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 ```js 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') ``` In `.delete(TRUE)`, `TRUE` must be uppercase. ### Constructor | Chaining Method | Description | | --- | --- | | barrier( ) | Create a new Barrier node that emits a BarrierMessage periodically | ### Property Methods | Setters | Description | | --- | --- | | idle ( value time.Duration) | Emit barrier based on idle time since the last received message. Must be greater than zero and longer than the window period. | | period ( value time.Duration) | Emit barrier based on periodic timer. The timer is based on system clock rather than message time. Must be greater than zero. | | delete ( value Boolean) | Delete the group after processing each barrier. | | quiet ( ) | Suppress all error logging events from this node. | ### Chaining Methods [Alert](#alert), [Barrier](#barrier), [Bottom](#bottom), [ChangeDetect](#changedetect), [Combine](#combine), [Count](#count), [CumulativeSum](#cumulativesum), [Deadman](#deadman), [Default](#default), [Delete](#delete), [Derivative](#derivative), [Difference](#difference), [Distinct](#distinct), [Ec2Autoscale](#ec2autoscale), [Elapsed](#elapsed), [Eval](#eval), [First](#first), [Flatten](#flatten), [GroupBy](#groupby), [HoltWinters](#holtwinters), [HoltWintersWithFit](#holtwinterswithfit), [HttpOut](#httpout), [HttpPost](#httppost), [InfluxDBOut](#influxdbout), [Join](#join), [K8sAutoscale](#k8sautoscale), [KapacitorLoopback](#kapacitorloopback), [Last](#last), [Log](#log), [Max](#max), [Mean](#mean), [Median](#median), [Min](#min), [Mode](#mode), [MovingAverage](#movingaverage), [Percentile](#percentile), [Sample](#sample), [Shift](#shift), [Sideload](#sideload), [Spread](#spread), [StateCount](#statecount), [StateDuration](#stateduration), [Stats](#stats), [Stddev](#stddev), [Sum](#sum), [SwarmAutoscale](#swarmautoscale), [Top](#top), [Trickle](#trickle), [Union](#union), [Where](#where), [Window](#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`**. ```js barrier.idle(value time.Duration) ``` #### Barrier idle time and window period `idle` must be greater than `period` of the associated [window](/kapacitor/v1/reference/nodes/window_node/). If `idle` times are less than the window `period`, data may be lost. ### Period Emit barrier based on periodic timer. The timer is based on system clock rather than message time. Must be greater than zero. ```js 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. ```js barrier.delete() ``` `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?](/kapacitor/v1/troubleshooting/frequently-asked-questions/#how-can-i-optimize-kapacitor-tasks) ### Quiet Suppress all error logging events from this node. ```js 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. ```js barrier|alert() ``` Returns: [AlertNode](/kapacitor/v1/reference/nodes/alert_node/) ### Barrier Create a new Barrier node that emits a BarrierMessage periodically. One BarrierMessage will be emitted every period duration. ```js barrier|barrier() ``` Returns: [BarrierNode](/kapacitor/v1/reference/nodes/barrier_node/) ### Bottom Select the bottom `num` points for `field` and sort by any extra tags or fields. ```js barrier|bottom(num int64, field string, fieldsAndTags ...string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### ChangeDetect Create a new node that only emits new points if different from the previous point. ```js barrier|changeDetect(field string) ``` Returns: [ChangeDetectNode](/kapacitor/v1/reference/nodes/change_detect_node/) ### Combine Combine this node with itself. The data is combined on timestamp. ```js barrier|combine(expressions ...ast.LambdaNode) ``` Returns: [CombineNode](/kapacitor/v1/reference/nodes/combine_node/) ### Count Count the number of points. ```js barrier|count(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### CumulativeSum Compute a cumulative sum of each point that is received. A point is emitted for every point collected. ```js barrier|cumulativeSum(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### 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: ```js 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: ```js 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](/kapacitor/v1/reference/nodes/alert_node/) is the last piece it can be further modified as usual. Example: ```js 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: ```js 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... ``` ```js barrier|deadman(threshold float64, interval time.Duration, expr ...ast.LambdaNode) ``` Returns: [AlertNode](/kapacitor/v1/reference/nodes/alert_node/) ### Default Create a node that can set defaults for missing tags or fields. ```js barrier|default() ``` Returns: [DefaultNode](/kapacitor/v1/reference/nodes/default_node/) ### Delete Create a node that can delete tags or fields. ```js barrier|delete() ``` Returns: [DeleteNode](/kapacitor/v1/reference/nodes/delete_node/) ### Derivative Create a new node that computes the derivative of adjacent points. ```js barrier|derivative(field string) ``` Returns: [DerivativeNode](/kapacitor/v1/reference/nodes/derivative_node/) ### Difference Compute the difference between points independent of elapsed time. ```js barrier|difference(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Distinct Produce batch of only the distinct points. ```js barrier|distinct(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Ec2Autoscale Create a node that can trigger autoscale events for a ec2 autoscalegroup. ```js barrier|ec2Autoscale() ``` Returns: [Ec2AutoscaleNode](/kapacitor/v1/reference/nodes/ec2_autoscale_node/) ### Elapsed Compute the elapsed time between points. ```js barrier|elapsed(field string, unit time.Duration) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### 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. ```js barrier|eval(expressions ...ast.LambdaNode) ``` Returns: [EvalNode](/kapacitor/v1/reference/nodes/eval_node/) ### First Select the first point. ```js barrier|first(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Flatten Flatten points with similar times into a single point. ```js barrier|flatten() ``` Returns: [FlattenNode](/kapacitor/v1/reference/nodes/flatten_node/) ### GroupBy Group the data by a set of tags. Can pass literal \* to group by all dimensions. Example: ```js |groupBy(*) ``` ```js barrier|groupBy(tag ...interface{}) ``` Returns: [GroupByNode](/kapacitor/v1/reference/nodes/group_by_node/) ### HoltWinters Compute the Holt-Winters (/influxdb/v1/query\_language/functions/#holt-winters) forecast of a data set. ```js barrier|holtWinters(field string, h int64, m int64, interval time.Duration) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### 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. ```js barrier|holtWintersWithFit(field string, h int64, m int64, interval time.Duration) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### 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/` and endpoint is `top10`, then the data can be requested from `/kapacitor/v1/tasks//top10`. ```js barrier|httpOut(endpoint string) ``` Returns: [HTTPOutNode](/kapacitor/v1/reference/nodes/http_out_node/) ### 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. ```js barrier|httpPost(url ...string) ``` Returns: [HTTPPostNode](/kapacitor/v1/reference/nodes/http_post_node/) ### InfluxDBOut Create an influxdb output node that will store the incoming data into InfluxDB. ```js barrier|influxDBOut() ``` Returns: [InfluxDBOutNode](/kapacitor/v1/reference/nodes/influx_d_b_out_node/) ### Join Join this node with other nodes. The data is joined on timestamp. ```js barrier|join(others ...Node) ``` Returns: [JoinNode](/kapacitor/v1/reference/nodes/join_node/) ### K8sAutoscale Create a node that can trigger autoscale events for a kubernetes cluster. ```js barrier|k8sAutoscale() ``` Returns: [K8sAutoscaleNode](/kapacitor/v1/reference/nodes/k8s_autoscale_node/) ### KapacitorLoopback Create an kapacitor loopback node that will send data back into Kapacitor as a stream. ```js barrier|kapacitorLoopback() ``` Returns: [KapacitorLoopbackNode](/kapacitor/v1/reference/nodes/kapacitor_loopback_node/) ### Last Select the last point. ```js barrier|last(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Log Create a node that logs all data it receives. ```js barrier|log() ``` Returns: [LogNode](/kapacitor/v1/reference/nodes/log_node/) ### Max Select the maximum point. ```js barrier|max(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Mean Compute the mean of the data. ```js barrier|mean(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### 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)`. ```js barrier|median(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Min Select the minimum point. ```js barrier|min(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Mode Compute the mode of the data. ```js barrier|mode(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### MovingAverage Compute a moving average of the last window points. No points are emitted until the window is full. ```js barrier|movingAverage(field string, window int64) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Percentile Select a point at the given percentile. This is a selector function, no interpolation between points is performed. ```js barrier|percentile(field string, percentile float64) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Sample Create a new node that samples the incoming points or batches. One point will be emitted every count or duration specified. ```js barrier|sample(rate interface{}) ``` Returns: [SampleNode](/kapacitor/v1/reference/nodes/sample_node/) ### Shift Create a new node that shifts the incoming points or batches in time. ```js barrier|shift(shift time.Duration) ``` Returns: [ShiftNode](/kapacitor/v1/reference/nodes/shift_node/) ### Sideload Create a node that can load data from external sources. ```js barrier|sideload() ``` Returns: [SideloadNode](/kapacitor/v1/reference/nodes/sideload_node/) ### Spread Compute the difference between `min` and `max` points. ```js barrier|spread(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### StateCount Create a node that tracks number of consecutive points in a given state. ```js barrier|stateCount(expression ast.LambdaNode) ``` Returns: [StateCountNode](/kapacitor/v1/reference/nodes/state_count_node/) ### StateDuration Create a node that tracks duration in a given state. ```js barrier|stateDuration(expression ast.LambdaNode) ``` Returns: [StateDurationNode](/kapacitor/v1/reference/nodes/state_duration_node/) ### 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. ```js barrier|stats(interval time.Duration) ``` Returns: [StatsNode](/kapacitor/v1/reference/nodes/stats_node/) ### Stddev Compute the standard deviation. ```js barrier|stddev(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Sum Compute the sum of all values. ```js barrier|sum(field string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### SwarmAutoscale Create a node that can trigger autoscale events for a Docker swarm cluster. ```js barrier|swarmAutoscale() ``` Returns: [SwarmAutoscaleNode](/kapacitor/v1/reference/nodes/swarm_autoscale_node/) ### Top Select the top `num` points for `field` and sort by any extra tags or fields. ```js barrier|top(num int64, field string, fieldsAndTags ...string) ``` Returns: [InfluxQLNode](/kapacitor/v1/reference/nodes/influx_q_l_node/) ### Trickle Create a new node that converts batch data to stream data. ```js barrier|trickle() ``` Returns: [TrickleNode](/kapacitor/v1/reference/nodes/trickle_node/) ### Union Perform the union of this node and all other given nodes. ```js barrier|union(node ...Node) ``` Returns: [UnionNode](/kapacitor/v1/reference/nodes/union_node/) ### Where Create a new node that filters the data stream by a given expression. ```js barrier|where(expression ast.LambdaNode) ``` Returns: [WhereNode](/kapacitor/v1/reference/nodes/where_node/) ### Window Create a new node that windows the stream by time. NOTE: Window can only be applied to stream edges. ```js barrier|window() ``` Returns: [WindowNode](/kapacitor/v1/reference/nodes/window_node/)