183 lines
5.5 KiB
Markdown
183 lines
5.5 KiB
Markdown
---
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title: StreamNode (Kapacitor TICKscript node)
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description: StreamNode represents the source of data being streamed to Kapacitor through any of its inputs.
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note: Auto generated by tickdoc
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menu:
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kapacitor_1_4:
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name: StreamNode
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identifier: stream_node
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weight: 290
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parent: TICKscript nodes
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---
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### Constructor
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| Chaining Method | Description |
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|:---------|:---------|
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| **[stream](#descr)** | Has no constructor signature. |
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### Property Methods
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This node has no properties that can be set.
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### Chaining Methods
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[Deadman](/kapacitor/v1.4/nodes/stream_node/#deadman), [From](/kapacitor/v1.4/nodes/stream_node/#from), [Stats](/kapacitor/v1.4/nodes/stream_node/#stats)
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<a id='descr'/><hr/><br/>
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### Description
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A [StreamNode](/kapacitor/v1.4/nodes/stream_node/) represents the source of data being
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streamed to Kapacitor through any of its inputs.
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The `stream` variable in stream tasks is an instance of
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a [StreamNode.](/kapacitor/v1.4/nodes/stream_node/)
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[StreamNode.From](/kapacitor/v1.4/nodes/stream_node/#from) is the method/property of this node.
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<a class="top" href="javascript:document.getElementsByClassName('article-heading')[0].scrollIntoView();" title="top"><span class="icon arrow-up"></span></a>
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Chaining Methods
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----------------
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Chaining methods create a new node in the pipeline as a child of the calling node.
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They do not modify the calling node.
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Chaining methods are marked using the `|` operator.
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### Deadman
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Helper function for creating an alert on low throughput, a.k.a. deadman's switch.
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- Threshold -- trigger alert if throughput drops below threshold in points/interval.
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- Interval -- how often to check the throughput.
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- Expressions -- optional list of expressions to also evaluate. Useful for time of day alerting.
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Example:
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```javascript
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var data = stream
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|from()...
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// Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
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data
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|deadman(100.0, 10s)
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//Do normal processing of data
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data...
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```
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The above is equivalent to this
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Example:
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```javascript
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var data = stream
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|from()...
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// Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
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data
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|stats(10s)
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.align()
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|derivative('emitted')
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.unit(10s)
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.nonNegative()
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|alert()
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.id('node \'stream0\' in task \'{{ .TaskName }}\'')
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.message('{{ .ID }} is {{ if eq .Level "OK" }}alive{{ else }}dead{{ end }}: {{ index .Fields "emitted" | printf "%0.3f" }} points/10s.')
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.crit(lambda: "emitted" <= 100.0)
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//Do normal processing of data
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data...
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```
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The `id` and `message` alert properties can be configured globally via the 'deadman' configuration section.
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Since the [AlertNode](/kapacitor/v1.4/nodes/alert_node/) is the last piece it can be further modified as usual.
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Example:
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```javascript
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var data = stream
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|from()...
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// Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
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data
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|deadman(100.0, 10s)
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.slack()
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.channel('#dead_tasks')
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//Do normal processing of data
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data...
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```
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You can specify additional lambda expressions to further constrain when the deadman's switch is triggered.
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Example:
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```javascript
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var data = stream
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|from()...
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// Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
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// Only trigger the alert if the time of day is between 8am-5pm.
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data
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|deadman(100.0, 10s, lambda: hour("time") >= 8 AND hour("time") <= 17)
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//Do normal processing of data
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data...
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```
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```javascript
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stream|deadman(threshold float64, interval time.Duration, expr ...ast.LambdaNode)
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```
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Returns: [AlertNode](/kapacitor/v1.4/nodes/alert_node/)
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<a class="top" href="javascript:document.getElementsByClassName('article-heading')[0].scrollIntoView();" title="top"><span class="icon arrow-up"></span></a>
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### From
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Creates a new [FromNode](/kapacitor/v1.4/nodes/from_node/) that can be further
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filtered using the Database, RetentionPolicy, Measurement and Where properties.
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From can be called multiple times to create multiple
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independent forks of the data stream.
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Example:
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```javascript
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// Select the 'cpu' measurement from just the database 'mydb'
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// and retention policy 'myrp'.
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var cpu = stream
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|from()
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.database('mydb')
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.retentionPolicy('myrp')
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.measurement('cpu')
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// Select the 'load' measurement from any database and retention policy.
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var load = stream
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|from()
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.measurement('load')
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// Join cpu and load streams and do further processing.
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cpu
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|join(load)
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.as('cpu', 'load')
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...
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```
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```javascript
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stream|from()
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```
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Returns: [FromNode](/kapacitor/v1.4/nodes/from_node/)
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<a class="top" href="javascript:document.getElementsByClassName('article-heading')[0].scrollIntoView();" title="top"><span class="icon arrow-up"></span></a>
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### Stats
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Create a new stream of data that contains the internal statistics of the node.
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The interval represents how often to emit the statistics based on real time.
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This means the interval time is independent of the times of the data points the source node is receiving.
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```javascript
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stream|stats(interval time.Duration)
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```
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Returns: [StatsNode](/kapacitor/v1.4/nodes/stats_node/)
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<a class="top" href="javascript:document.getElementsByClassName('article-heading')[0].scrollIntoView();" title="top"><span class="icon arrow-up"></span></a>
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