Template reference

Prometheus supports templating in the annotations and labels 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  interface{}
}

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.

Functions

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.

Queries

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	interface{}	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.

Numbers

Name	Arguments	Returns	Notes
humanize	number or string	string	Converts a number to a more readable format, using metric prefixes.
humanize1024	number or string	string	Like humanize, but uses 1024 as the base rather than 1000.
humanizeDuration	number or string	string	Converts a duration in seconds to a more readable format.
humanizePercentage	number or string	string	Converts a ratio value to a fraction of 100.
humanizeTimestamp	number or string	string	Converts a Unix timestamp in seconds to a more readable format.
toTime	number or string	*time.Time	Converts a Unix timestamp in seconds to a time.Time.

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

Strings

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.
stripPort	string	string	net.SplitHostPort, splits string into host and port, then returns only host.
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 ("Table") view in the expression browser for the expression.
parseDuration	string	float	Parses a duration string such as "1h" into the number of seconds it represents.
stripDomain	string	string	Removes the domain part of a FQDN. Leaves port untouched.

Others

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.
externalURL	none	string	The external URL under which Prometheus is externally reachable.
pathPrefix	none	string	The external URL path for use in console templates.

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, .Labels, .ExternalLabels, and .ExternalURL contain the alert value, the alert labels, the globally configured external labels, and the external URL (configured with --web.external-url) respectively. They are also exposed as the $value, $labels, $externalLabels, and $externalURL 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. The globally configured external labels are available as .ExternalLabels. There are also convenience variables for all four: $rawParams, $params, $path, and $externalLabels.

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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