Prometheus (software)

Prometheus data is stored in the form of metrics, with each metric having a name that is used for referencing and querying it. Each metric can be drilled down by an arbitrary number of key=value pairs (labels). Labels can include information on the data source (which server the data is coming from) and other application-specific breakdown information such as the HTTP status code (for metrics related to HTTP responses), query method (GET versus POST), endpoint, etc. The ability to specify an arbitrary list of labels and to query based on these in real time is why Prometheus' data model is called multi-dimensional.[16][8][9]

Prometheus stores data locally on disk, which helps for fast data storage and fast querying.[8] There is the ability to store metrics in remote storage.[17]

Prometheus collects data in the form of time series. The time series are built through a pull model: the Prometheus server queries a list of data sources (sometimes called exporters) at a specific polling frequency. Each of the data sources serves the current values of the metrics for that data source at the endpoint queried by Prometheus. The Prometheus server then aggregates data across the data sources.[8] Prometheus has a number of mechanisms to automatically discover resources that should be used as data sources.[18]

Prometheus provides its own query language PromQL (Prometheus Query Language) that lets users select and aggregate data. PromQL is specifically adjusted to work in convention with a Time-Series Database and therefore provides time-related query functionalities. Examples include the rate() function, the instant vector and the range vector which can provide many samples for each queried time series.[19] Prometheus has four clearly defined metric types around which the PromQL components revolve. The four types are

• Gauge
• Counter
• Histogram
• Summary

Configuration for alerts can be specified in Prometheus which specifies a condition that needs to be maintained for a specific duration in order for an alert to trigger. When alerts trigger, they are forwarded to the Alertmanager service. Alertmanager can include logic to silence alerts and also to forward them to email, Slack, or notification services such as PagerDuty.[20] Some other messaging systems like Microsoft Teams[21] could be configured using the Alertmanager Webhook Receiver as a mechanism for external integrations.[22] also Prometheus Alerts can be used to receive alerts directly on android devices even without the requirement of any targets configuration in Alert Manager.[23]

Prometheus is not intended as a full-fledged dashboard. Although it can be used to graph specific queries, it is not a full-fledged dashboard and needs to be hooked up with Grafana to generate dashboards; this has been cited as a disadvantage due to the additional setup complexity.[24]

Prometheus favors white-box monitoring. Applications are encouraged to publish (export) internal metrics to be collected periodically by Prometheus.[25] Some exporters and agents for various applications are available to provide metrics.[26] Prometheus supports some monitoring and administration protocols to allow interoperability for transitioning: Graphite, StatsD, SNMP, JMX, and CollectD.

Prometheus focuses on the availability of the platform and basic operations.[27] The metrics are typically stored for a few weeks. For long-term storage, the metrics can be streamed to remote storage.[17]

There is an effort to promote Prometheus exposition format into a standard known as OpenMetrics.[28] Some products adopted the format: InfluxData's TICK suite,[29] InfluxDB, Google Cloud Platform,[30] and DataDog.[31]