Glossary

aggregator

Central service acting as a publisher of a feed that carries data points pertaining to all hosts. This feed is effectively a union of forwarder and poller feeds.

controller

Central service responsible for cluster management.

data point

Numeric value obtained by reading of a statistic at a specific time. Element of a time series. Every line output by a plugin is a data point.

In a line plot, it corresponds to every (x,y) that contributes to line's shape.

feed

TCP connection carrying real-time stream of recently extracted data points. Produced by forwarder, poller, and aggregator.

filter

Ruleset used to drop data points received from plugins, or to rewrite them before publishing to subscribers.

forwarder

Agent distributed to every host. Publisher of a feed that carries data points pertaining to the local host.

plugin

User program running a loop that extracts data points from the local host (if executed by forwarder) or from remote hosts (if executed by poller). It submits these points to forwarder/poller for filtering and delivery to subscribers.

poller

Central service acting as a publisher of a feed that carries data points pertaining to remote hosts (e.g. SNMP devices).

statse

Plugin responsible for deriving data points from event streams (e.g. web logs) through continuous statistical aggregation.

subscriber

User program that consumes the feed.

1. Indirect: receives data points from aggregator.
2. Direct receives points from forwarders and the poller.

time series

Sequence of data points created by periodically reading the value of a statistic (e.g. cpu utilization of the local host).

In a line plot, it corresponds to the line itself.

time series identifier

Human-readable name of a time series.

The identifier consists of two sections:

1. Metric: A dot-delimited string that represents a broad category of time series (e.g. os.filesystem.usage).
2. Tags: List of key=value pairs that subdivide metric along independent dimensions (e.g. host=localhost,mount=/var/log).

In a line plot, it corresponds to line's label in the legend (key) section.