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array

The array namespace contains functions related to arrays.

array.concat

The array.concat function concatenates one or more lists of values into a single list. Each argument to array.concat must be a list value. Elements within the list can be any type.

Examples

alloy 
> array.concat([])
[]

> array.concat([1, 2], [3, 4])
[1, 2, 3, 4]

> array.concat([1, 2], [], [bool, null])
[1, 2, bool, null]

> array.concat([[1, 2], [3, 4]], [[5, 6]])
[[1, 2], [3, 4], [5, 6]]

array.combine_maps

EXPERIMENTAL: This is an experimental feature. Experimental features are subject to frequent breaking changes, and may be removed with no equivalent replacement. To enable and use an experimental feature, you must set the stability.level flag to experimental.

The array.combine_maps function allows you to join two arrays of maps if certain keys have matching values in both maps. It’s particularly useful when combining labels of targets coming from different prometheus.discovery.* or prometheus.exporter.* components. It takes three arguments:

  • The first two arguments are a of type list(map(string)). The keys of the map are strings. The value for each key could be of any Alloy type such as a string, integer, map, or a capsule.
  • The third input is an array containing strings. The strings are the keys whose value has to match for maps to be combined.
  • (optional) The fourth input is a boolean which defaults to false. When it is set to true, each item from the first argument will be passed through even if there is no match. This is helpful if you want to enrich the first list with attributes from the second list, without losing any of the information from the first list.

The maps that don’t contain all the keys provided in the third argument will be discarded. When maps are combined and both contain the same keys, the last value from the second argument will be used.

Pseudo function code:

text 
for every map in arg1:
  for every map in arg2:
    if the condition key matches in both:
       merge maps and add to result

Examples

alloy 
> array.combine_maps([{"instance"="1.1.1.1", "team"="A"}], [{"instance"="1.1.1.1", "cluster"="prod"}], ["instance"])
[{"instance"="1.1.1.1", "team"="A", "cluster"="prod"}]

// Second map overrides the team in the first map
> array.combine_maps([{"instance"="1.1.1.1", "team"="A"}], [{"instance"="1.1.1.1", "team"="B"}], ["instance"])
[{"instance"="1.1.1.1", "team"="B"}]

// If multiple maps from the first argument match with multiple maps from the second argument, different combinations will be created.
> array.combine_maps([{"instance"="1.1.1.1", "team"="A"}, {"instance"="1.1.1.1", "team"="B"}], [{"instance"="1.1.1.1", "cluster"="prod"}, {"instance"="1.1.1.1", "cluster"="ops"}], ["instance"])
[{"instance"="1.1.1.1", "team"="A", "cluster"="prod"}, {"instance"="1.1.1.1", "team"="A", "cluster"="ops"}, {"instance"="1.1.1.1", "team"="B", "cluster"="prod"}, {"instance"="1.1.1.1", "team"="B", "cluster"="ops"}]

Examples using discovery and exporter components:

alloy 
> array.combine_maps(prometheus.exporter.postgres.example.targets, discovery.kubernetes.k8s_pods.targets, ["instance"], true)

> array.combine_maps(prometheus.exporter.redis.default.targets, [{"instance"="1.1.1.1", "testLabelKey" = "testLabelVal"}], ["instance"], true)

In the examples above the fourth argument is set to true so that the original targets from the exporters will still be preserved and scraped even if they cannot be enriched with values from the second argument.

You can find more examples in the tests.

Note

array.combine_maps can be useful for enriching Prometheus service discovery targets prior to a Prometheus scrape. It cannot be used to enrich Prometheus metrics with labels from service discovery components. You can use the [prometheus.enrich][] component for this purpose.

prometheus.enrich

array.group_by

EXPERIMENTAL: This is an experimental feature. Experimental features are subject to frequent breaking changes, and may be removed with no equivalent replacement. To enable and use an experimental feature, you must set the stability.level flag to experimental.

The array.group_by function groups an array of objects by a given key.

  • The first argument is an array of objects.
  • The second argument is a string that is the key to group by. The value of the key must be a string and should be present at the top level of the object.
  • The third argument is a boolean that indicates whether the elements that don’t match the key should be dropped (true) or added to the empty group (false).

Examples

alloy 
> array.group_by([{"type" = "fruit", "name" = "apple"}, {"type" = "fruit", "name" = "banana"}, {"type" = "vegetable", "name" = "carrot"}, {"name" = "rock"}], "type", false)
[{"type" = "fruit", "items" = [{"type" = "fruit", "name" = "apple"}, {"type" = "fruit", "name" = "banana"}]}, {"type" = "vegetable", "items" = [{"type" = "vegetable", "name" = "carrot"}]}, {"type" = "", "items" = [{"name" = "rock"}]}]

> array.group_by([{"type" = "fruit", "name" = "apple"}, {"type" = "fruit", "name" = "banana"}, {"type" = "vegetable", "name" = "carrot"}, {"name" = "rock"}], "type", true)
[{"type" = "fruit", "items" = [{"type" = "fruit", "name" = "apple"}, {"type" = "fruit", "name" = "banana"}]}, {"type" = "vegetable", "items" = [{"type" = "vegetable", "name" = "carrot"}]}]

The following example shows how to use the array.group_by function with a foreach block to group targets by match labels and create a prometheus.scrape component for each group dynamically. The targets in this example should have a label “match” that contains instant vector selectors separated by slash (refer to Federation for more information on the match parameter).

alloy 
foreach "federation" {
 collection = array.group_by(discovery.file.example.targets, "match", false)
 var = "each"
 id  = "match"

 template {
   prometheus.scrape "default" {
     targets    = each["items"]
     honor_labels = true
     metrics_path = "/federate"
     params = {
       "match[]" = string.split(coalesce(each["match"], "{__name__!=\"\"}"), "/"),
     }
     forward_to = [prometheus.remote_write.default.receiver]
   }
 }
}