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116 changes: 116 additions & 0 deletions docs/configuration/template_examples.md
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---
title: Template examples
sort_rank: 4
---

# Template examples

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](http://golang.org/pkg/text/template/) system.

## Simple alert field templates

ALERT InstanceDown
IF up == 0
FOR 5m
LABELS {
severity="page"
}
ANNOTATIONS {
summary = "Instance {{$labels.instance}} down",
description = "{{$labels.instance}} of job {{$labels.job}} has been down for more than 5 minutes.",
}

Alert field templates will be executed during every rule iteration for each
alert that fires, so keep any queries and templates lightweight. If you have a
need for more complicated templates for alerts, it is recommended to link to a
console instead.

## Simple iteration

This displays a list of instances, and whether they are up:

```go
{{ range query "up" }}
{{ .Labels.instance }} {{ .Value }}
{{ end }}
```

The special `.` variable contains the value of the current sample for each loop iteration.

## Display one value

```go
{{ with query "some_metric{instance='someinstance'}" }}
{{ . | first | value | humanize }}
{{ end }}
```

Go and Go's templating language are both strongly typed, so one must check that
samples were returned to avoid an execution error. For example this could
happen if a scrape or rule evaluation has not run yet, or a host was down.

The included `prom_query_drilldown` template handles this, allows for
formatting of results, and linking to the [expression browser](https://prometheus.io/docs/visualization/browser/).

## Using console URL parameters

```go
{{ with printf "node_memory_MemTotal{job='node',instance='%s'}" .Params.instance | query }}
{{ . | first | value | humanize1024}}B
{{ end }}
```

If accessed as `console.html?instance=hostname`, `.Params.instance` will evaluate to `hostname`.

## Advanced iteration

```html
<table>
{{ range printf "node_network_receive_bytes{job='node',instance='%s',device!='lo'}" .Params.instance | query | sortByLabel "device"}}
<tr><th colspan=2>{{ .Labels.device }}</th></tr>
<tr>
<td>Received</td>
<td>{{ with printf "rate(node_network_receive_bytes{job='node',instance='%s',device='%s'}[5m])" .Labels.instance .Labels.device | query }}{{ . | first | value | humanize }}B/s{{end}}</td>
</tr>
<tr>
<td>Transmitted</td>
<td>{{ with printf "rate(node_network_transmit_bytes{job='node',instance='%s',device='%s'}[5m])" .Labels.instance .Labels.device | query }}{{ . | first | value | humanize }}B/s{{end}}</td>
</tr>{{ end }}
<table>
```

Here we iterate over all network devices and display the network traffic for each.

As the `range` action does not specify a variable, `.Params.instance` is not
available inside the loop as `.` is now the loop variable.

## Defining reusable templates

Prometheus supports defining templates that can be reused. This is particularly
powerful when combined with
[console library](template_reference.md#console-templates) support, allowing
sharing of templates across consoles.

```go
{{/* Define the template */}}
{{define "myTemplate"}}
do something
{{end}}

{{/* Use the template */}}
{{template "myTemplate"}}
```

Templates are limited to one argument. The `args` function can be used to wrap multiple arguments.

```go
{{define "myMultiArgTemplate"}}
First argument: {{.arg0}}
Second argument: {{.arg1}}
{{end}}
{{template "myMultiArgTemplate" (args 1 2)}}
```
114 changes: 114 additions & 0 deletions docs/configuration/template_reference.md
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---
title: Template reference
sort_rank: 5
---

# 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](http://golang.org/pkg/text/template/) system.

## Data Structures

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

```go
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.

## Functions

In addition to the [default
functions](http://golang.org/pkg/text/template/#hdr-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 | 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.

### Numbers

| Name | Arguments | Returns | Notes |
| ------------- | --------------| --------| --------- |
| humanize | number | string | Converts a number to a more readable format, using [metric prefixes](http://en.wikipedia.org/wiki/Metric_prefix).
| 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.

### Strings

| Name | Arguments | Returns | Notes |
| ------------- | ------------- | ------- | ----------- |
| title | string | string | [strings.Title](http://golang.org/pkg/strings/#Title), capitalises first character of each word.|
| toUpper | string | string | [strings.ToUpper](http://golang.org/pkg/strings/#ToUpper), converts all characters to upper case.|
| toLower | string | string | [strings.ToLower](http://golang.org/pkg/strings/#ToLower), converts all characters to lower case.|
| match | pattern, text | boolean | [regexp.MatchString](http://golang.org/pkg/regexp/#MatchString) Tests for a unanchored regexp match. |
| reReplaceAll | pattern, replacement, text | string | [Regexp.ReplaceAllString](http://golang.org/pkg/regexp/#Regexp.ReplaceAllString) Regexp substitution, unanchored. |
| graphLink | expr | string | Returns path to graph view in the [expression browser](https://prometheus.io/docs/visualization/browser/) for the expression. |
| tableLink | expr | string | Returns path to tabular ("Console") view in the [expression browser](https://prometheus.io/docs/visualization/browser/) for the expression. |

### 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. |

## 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](http://golang.org/pkg/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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