Resource Blocks
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Resources are the most important element in the Terraform language. Each resource block describes one or more infrastructure objects, such as virtual networks, compute instances, or higher-level components such as DNS records.
For information about how Terraform manages resources after applying a configuration, refer to Resource Behavior.
Resource Syntax
A resource
block declares a resource of a specific type
with a specific local name. Terraform uses the name when referring to the resource
in the same module, but it has no meaning outside that module's scope.
In the following example, the aws_instance
resource type is named web
. The resource type and name must be unique within a module because they serve as an identifier for a given resource.
Within the block body (between {
and }
) are the configuration arguments
for the resource itself. The arguments often depend on the
resource type. In this example, both ami
and instance_type
are special
arguments for the aws_instance
resource type.
Note: Resource names must start with a letter or underscore, and may contain only letters, digits, underscores, and dashes.
Resource declarations can include more advanced features, such as single resource declarations that produce multiple similar remote objects, but only a small subset is required for initial use.
Resource Types
Each resource is associated with a single resource type, which determines the kind of infrastructure object it manages and what arguments and other attributes the resource supports.
Providers
A provider is a plugin for Terraform that offers a collection of resource types. Each resource type is implemented by a provider. A provider provides resources to manage a single cloud or on-premises infrastructure platform. Providers are distributed separately from Terraform, but Terraform can automatically install most providers when initializing a working directory.
To manage resources, a Terraform module must specify the required providers. Refer to Provider Requirements for additional information.
Most providers need some configuration to access their remote API, which is provided by the root module. Refer to Provider Configuration for additional information.
Based on a resource type's name, Terraform can usually determine which provider to use.
By convention, resource type names start with their provider's preferred local name.
When using multiple configurations of a provider or non-preferred local provider names,
you must use the provider
meta-argument
to manually choose a provider configuration.
Resource Arguments
Most of the arguments within the body of a resource
block are specific to the
selected resource type. The resource type's documentation lists which arguments
are available and how their values should be formatted.
The values for resource arguments can make full use of expressions and other dynamic Terraform language features.
Meta-arguments are defined by Terraform and apply across all resource types.
Documentation for Resource Types
Every Terraform provider has its own documentation, describing its resource types and their arguments.
Some provider documentation is still part of Terraform's core documentation, but the Terraform Registry is the main home for all publicly available provider docs.
When viewing a provider's page on the Terraform Registry, you can click the Documentation link in the header to browse its documentation. The documentation is versioned. To choose a different version of the provider documentation, click on the version in the provider breadcrumbs to choose a version from the drop-down menu.
Meta-Arguments
The Terraform language defines the following meta-arguments, which can be used with any resource type to change the behavior of resources:
depends_on
, for specifying hidden dependenciescount
, for creating multiple resource instances according to a countfor_each
, to create multiple instances according to a map, or set of stringsprovider
, for selecting a non-default provider configurationlifecycle
, for lifecycle customizationsprovisioner
, for taking extra actions after resource creation
Removing Resources
Note: The removed
block is available in Terraform v1.7 and later. For earlier Terraform versions, you can use the terraform state rm
CLI command as a separate step.
To remove a resource from Terraform, simply delete the resource
block from your Terraform configuration.
By default, after you remove the resource
block, Terraform will plan to destroy any real infrastructure object managed by that resource.
Sometimes you may wish to remove a resource from your Terraform configuration without destroying the real infrastructure object it manages. In this case, the resource will be removed from the Terraform state, but the real infrastructure object will not be destroyed.
To declare that a resource was removed from Terraform configuration but that its managed object should not be destroyed, remove the resource
block from your configuration and replace it with a removed
block:
The from
argument is the address of the resource you want to remove, without any instance keys (such as "aws_instance.example[1]").
The lifecycle
block is required. The destroy
argument determines whether Terraform will attempt to destroy the object managed by the resource or not. A value of false
means that Terraform will remove the resource from state without destroying it.
Custom Condition Checks
You can use precondition
and postcondition
blocks to specify assumptions and guarantees about how the resource operates. The following example creates a precondition that checks whether the AMI is properly configured.
Custom condition checks can help capture assumptions so that future maintainers understand the configuration design and intent. They also return useful information about errors earlier and in context, helping consumers to diagnose issues in their configuration.
Operation Timeouts
Some resource types provide a special timeouts
nested block argument that
allows you to customize how long certain operations are allowed to take
before being considered to have failed.
For example, aws_db_instance
allows configurable timeouts for create
, update
, and delete
operations.
Timeouts are handled entirely by the resource type implementation in the
provider, but resource types offering these features follow the convention
of defining a child block called timeouts
that has a nested argument
named after each operation that has a configurable timeout value.
Each of these arguments takes a string representation of a duration, such
as "60m"
for 60 minutes, "10s"
for ten seconds, or "2h"
for two hours.
The set of configurable operations is chosen by each resource type. Most
resource types do not support the timeouts
block at all. Consult the
documentation for each resource type to see which operations it offers
for configuration, if any.