Requirements (Extra Resources)

The requirement block lets you request extra resources from Crossplane. These are typically used to read configuration data (like EnvironmentConfig objects) that aren’t part of the composition’s resource tree.

Syntax

requirement <name> {
  condition = <bool>    # optional
  locals { ... }        # optional

  select {
    apiVersion  = <string>
    kind        = <string>
    matchName   = <string>       # match by name
    # OR
    matchLabels = <map(string)>  # match by labels
  }
}

You must specify either matchName or matchLabels, but not both.

Match by Name

requirement my-config {
  select {
    apiVersion = "apiextensions.crossplane.io/v1beta1"
    kind       = "EnvironmentConfig"
    matchName  = "foo-bar"
  }
}

Match by Labels

requirement my-config {
  select {
    apiVersion  = "apiextensions.crossplane.io/v1beta1"
    kind        = "EnvironmentConfig"
    matchLabels = { foo = "bar" }
  }
}

Accessing Extra Resources

The name given to the requirement is the key in req.extra_resources. The value is always an array of matching objects, even when matching by name:

locals {
  # Access the first matching object
  myConfig     = req.extra_resources.my-config[0]
  myLabelValue = myConfig.metadata.labels["my-label"]
  myDataValue  = myConfig.data.labels
}

Conditional Requirements

Use condition to skip the requirement if certain conditions aren’t met:

requirement labels-config {
  condition = req.composite.metadata.labels["special"] == "true"

  locals {
    ecName = "foo-bar"
  }

  select {
    apiVersion = "apiextensions.crossplane.io/v1beta1"
    kind       = "EnvironmentConfig"
    matchName  = ecName
  }
}

The requirement is skipped if the condition evaluates to false. The usual rules for conditions apply.

Locals in Requirements

Local variables in a requirement block can be used as temporary variables for complex calculations that feed into the select block.

When Extra Resources Are Absent

If the requested resource doesn’t exist yet, req.extra_resources.<name> may be null or empty. Any resource block that references missing extra resources will be automatically deferred.

Error Conditions

The function returns an error if:

• A requirement block specifies both matchName and matchLabels
• A requirement block specifies neither matchName nor matchLabels
• There is a data type mismatch in the select attributes