Data Sources

Data sources allow data to be fetched or computed for use elsewhere in Terraform configuration. Use of data sources allows a Terraform configuration to build on information defined outside of Terraform, or defined by another separate Terraform configuration.

Providers are responsible in Terraform for defining and implementing data sources. Whereas a resource causes Terraform to create and manage a new infrastructure component, data sources present read-only views into pre-existing data, or they compute new values on the fly within Terraform itself.

For example, a data source may retrieve remote state data from a Terraform Cloud workspace, configuration information from Consul, or look up a pre-existing AWS resource by filtering on its attributes and tags.

Every data source in Terraform is mapped to a provider based on longest-prefix matching. For example the aws_ami data source would map to the aws provider (if that exists).

This page assumes you're familiar with the configuration syntax already.

Example

A data source configuration looks like the following:

# Find the latest available AMI that is tagged with Component = web
data "aws_ami" "web" {
  filter {
    name   = "state"
    values = ["available"]
  }

  filter {
    name   = "tag:Component"
    values = ["web"]
  }

  most_recent = true
}

Description

The data block creates a data instance of the given TYPE (first parameter) and NAME (second parameter). The combination of the type and name must be unique.

Within the block (the { }) is configuration for the data instance. The configuration is dependent on the type; consult the provider's documentation for details.

Each data instance will export one or more attributes, which can be interpolated into other resources using variables of the form data.TYPE.NAME.ATTR. For example:

resource "aws_instance" "web" {
  ami           = "${data.aws_ami.web.id}"
  instance_type = "t1.micro"
}

Meta-parameters

As data sources are essentially a read only subset of resources they also support the same meta-parameters of resources except for the lifecycle configuration block.

Multiple Provider Instances

Similarly to resources, the provider meta-parameter can be used where a configuration has multiple aliased instances of the same provider:

data "aws_ami" "web" {
  provider = "aws.west"

  # ...
}

See the "Multiple Provider Instances" documentation for resources for more information.

Data Source Lifecycle

If the arguments of a data instance contain no references to computed values, such as attributes of resources that have not yet been created, then the data instance will be read and its state updated during Terraform's "refresh" phase, which by default runs prior to creating a plan. This ensures that the retrieved data is available for use during planning and the diff will show the real values obtained.

Data instance arguments may refer to computed values, in which case the attributes of the instance itself cannot be resolved until all of its arguments are defined. In this case, refreshing the data instance will be deferred until the "apply" phase, and all interpolations of the data instance attributes will show as "computed" in the plan since the values are not yet known.