telegraf/docs/AGGREGATORS_AND_PROCESSORS.md

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# Telegraf Aggregator & Processor Plugins
As of release 1.1.0, Telegraf has the concept of Aggregator and Processor Plugins.
These plugins sit in-between Input & Output plugins, aggregating and processing
metrics as they pass through Telegraf:
```
┌───────────┐
│ │
│ CPU │───┐
│ │ │
└───────────┘ │
┌───────────┐ │ ┌───────────┐
│ │ │ │ │
│ Memory │───┤ ┌──▶│ InfluxDB │
│ │ │ │ │ │
└───────────┘ │ ┌─────────────┐ ┌─────────────┐ │ └───────────┘
│ │ │ │Aggregate │ │
┌───────────┐ │ │Process │ │ - mean │ │ ┌───────────┐
│ │ │ │ - transform │ │ - quantiles │ │ │ │
│ MySQL │───┼───▶│ - decorate │────▶│ - min/max │───┼──▶│ File │
│ │ │ │ - filter │ │ - count │ │ │ │
└───────────┘ │ │ │ │ │ │ └───────────┘
│ └─────────────┘ └─────────────┘ │
┌───────────┐ │ │ ┌───────────┐
│ │ │ │ │ │
│ SNMP │───┤ └──▶│ Kafka │
│ │ │ │ │
└───────────┘ │ └───────────┘
┌───────────┐ │
│ │ │
│ Docker │───┘
│ │
└───────────┘
```
Both Aggregators and Processors analyze metrics as they pass through Telegraf.
Use [measurement filtering](CONFIGURATION.md#measurement-filtering)
to control which metrics are passed through a processor or aggregator. If a
metric is filtered out the metric bypasses the plugin and is passed downstream
to the next plugin.
**Processor** plugins process metrics as they pass through and immediately emit
results based on the values they process. For example, this could be printing
all metrics or adding a tag to all metrics that pass through.
**Aggregator** plugins, on the other hand, are a bit more complicated. Aggregators
are typically for emitting new _aggregate_ metrics, such as a running mean,
minimum, maximum, quantiles, or standard deviation. For this reason, all _aggregator_
plugins are configured with a `period`. The `period` is the size of the window
of metrics that each _aggregate_ represents. In other words, the emitted
_aggregate_ metric will be the aggregated value of the past `period` seconds.
Since many users will only care about their aggregates and not every single metric
gathered, there is also a `drop_original` argument, which tells Telegraf to only
emit the aggregates and not the original metrics.
**NOTE** That since aggregators only aggregate metrics within their period, that
historical data is not supported. In other words, if your metric timestamp is more
than `now() - period` in the past, it will not be aggregated. If this is a feature
that you need, please comment on this [github issue](https://github.com/influxdata/telegraf/issues/1992)