--- title: KapacitorLoopbackNode description: KapacitorLoopbackNode writes data back into the Kapacitor stream. note: Auto generated by tickdoc menu: kapacitor_1_5_ref: name: KapacitorLoopback identifier: kapacitor_loopback_node weight: 190 parent: nodes --- The `kapacitorLoopback` node writes data back into the Kapacitor stream. To write data to a remote Kapacitor instance use the [InfluxDBOutNode](/kapacitor/v1.5/nodes/influx_d_b_out_node/). Example: ```js |kapacitorLoopback() .database('mydb') .retentionPolicy('myrp') .measurement('errors') .tag('kapacitor', 'true') .tag('version', '0.2') ``` {{% note %}} #### Beware of infinite loops It is possible to create infinite loops using the KapacitorLoopback node. Take care to ensure you do not chain tasks together creating a loop. {{% /note %}} {{% warn %}} #### Avoid name collisions with multiple subscriptions When using the KapacitorLoopback node, don't subscribe to identically named databases and retention policies in multiple InfluxDB instances or clusters. If Kapacitor is subscribed to multiple instances of InfluxDB, make each database and retention policy combination unique. For example: ``` influxdb_1 └─ db1/rp1 influxdb_2 └─ db2/rp2 ``` {{% /warn %}} Available Statistics: * `points_written`: number of points written back to Kapacitor ### Constructor | Chaining Method | Description | |:---------|:---------| | **kapacitorLoopback ( )** | Create an kapacitor loopback node that will send data back into Kapacitor as a stream. | ### Property Methods | Setters | Description | |:---|:---| | **[database](#database) ( `value` `string`)** | The name of the database. | | **[measurement](#measurement) ( `value` `string`)** | The name of the measurement. | | **[quiet](#quiet) ( )** | Suppress all error logging events from this node. | | **[retentionPolicy](#retentionpolicy) ( `value` `string`)** | The name of the retention policy. | | **[tag](#tag) ( `key` `string`, `value` `string`)** | Add a static tag to all data points. Tag can be called more than once. | ### Chaining Methods [Deadman](#deadman), [Stats](#stats) --- ## 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. ### Database The name of the database. ```js kapacitorLoopback.database(value string) ``` ### Measurement The name of the measurement. ```js kapacitorLoopback.measurement(value string) ``` ### Quiet Suppress all error logging events from this node. ```js kapacitorLoopback.quiet() ``` ### RetentionPolicy The name of the retention policy. ```js kapacitorLoopback.retentionPolicy(value string) ``` ### Tag Add a static tag to all data points. Tag can be called more than once. ```js kapacitorLoopback.tag(key string, value string) ``` ## 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: ```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/v1.5/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 kapacitorLoopback|deadman(threshold float64, interval time.Duration, expr ...ast.LambdaNode) ``` Returns: [AlertNode](/kapacitor/v1.5/nodes/alert_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 kapacitorLoopback|stats(interval time.Duration) ``` Returns: [StatsNode](/kapacitor/v1.5/nodes/stats_node/)