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Template reference

Prometheus supports templating in the summary and description fields of alerts, as well as in served console pages. Templates have the ability to run queries against the local database, iterate over data, use conditionals, format data, etc. The Prometheus templating language is based on the Go templating system.

Data Structures

The primary data structure for dealing with time series data is the sample, defined as:

type sample struct {
        Labels map[string]string
        Value  float64

The metric name of the sample is encoded in a special __name__ label in the Labels map.

[]sample means a list of samples.

interface{} in Go is similar to a void pointer in C.


In addition to the default functions provided by Go templating, Prometheus provides functions for easier processing of query results in templates.

If functions are used in a pipeline, the pipeline value is passed as the last argument.


Name Arguments Returns Notes
query query string []sample Queries the database, does not support returning range vectors.
first []sample sample Equivalent to index a 0
label label, sample string Equivalent to index sample.Labels label
value sample float64 Equivalent to sample.Value
sortByLabel label, []samples []sample Sorts the samples by the given label. Is stable.

first, label and value are intended to make query results easily usable in pipelines.


Name Arguments Returns Notes
humanize number string Converts a number to a more readable format, using metric prefixes.
humanize1024 number string Like humanize, but uses 1024 as the base rather than 1000.
humanizeDuration number string Converts a duration in seconds to a more readable format.
humanizeTimestamp number string Converts a Unix timestamp in seconds to a more readable format.

Humanizing functions are intended to produce reasonable output for consumption by humans, and are not guaranteed to return the same results between Prometheus versions.


Name Arguments Returns Notes
title string string strings.Title, capitalises first character of each word.
toUpper string string strings.ToUpper, converts all characters to upper case.
toLower string string strings.ToLower, converts all characters to lower case.
match pattern, text boolean regexp.MatchString Tests for a unanchored regexp match.
reReplaceAll pattern, replacement, text string Regexp.ReplaceAllString Regexp substitution, unanchored.
graphLink expr string Returns path to graph view in the expression browser for the expression.
tableLink expr string Returns path to tabular ("Console") view in the expression browser for the expression.


Name Arguments Returns Notes
args []interface{} map[string]interface{} This converts a list of objects to a map with keys arg0, arg1 etc. This is intended to allow multiple arguments to be passed to templates.
tmpl string, []interface{} nothing Like the built-in template, but allows non-literals as the template name. Note that the result is assumed to be safe, and will not be auto-escaped. Only available in consoles.
safeHtml string string Marks string as HTML not requiring auto-escaping.

Template type differences

Each of the types of templates provide different information that can be used to parameterize templates, and have a few other differences.

Alert field templates

.Value and .Labels contain the alert value and labels. They are also exposed as the $value and $labels variables for convenience.

Console templates

Consoles are exposed on /consoles/, and sourced from the directory pointed to by the -web.console.templates flag.

Console templates are rendered with html/template, which provides auto-escaping. To bypass the auto-escaping use the safe* functions.,

URL parameters are available as a map in .Params. To access multiple URL parameters by the same name, .RawParams is a map of the list values for each parameter. The URL path is available in .Path, excluding the /consoles/ prefix.

Consoles also have access to all the templates defined with {{define "templateName"}}...{{end}} found in *.lib files in the directory pointed to by the -web.console.libraries flag. As this is a shared namespace, take care to avoid clashes with other users. Template names beginning with prom, _prom, and __ are reserved for use by Prometheus, as are the functions listed above.

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