---
sidebar_label: s3
description: OpenTofu can store state remotely in S3 and lock that state with DynamoDB.
---

# Backend Type: s3

Stores the state as a given key in a given bucket on
[Amazon S3](https://aws.amazon.com/s3/).
This backend supports multiple locking mechanisms. The preferred one is a native S3 locking via
conditional writes with `If-None-Match` header. This can be enabled by setting `use_lockfile=true`.
Another option is to use [Dynamo DB](https://aws.amazon.com/dynamodb/) locking, which can be enabled by setting
the `dynamodb_table` field to an existing DynamoDB table name.
A single DynamoDB table can be used to lock multiple remote state files. OpenTofu generates key names that include the values of the `bucket` and `key` variables.

:::warning
It is highly recommended that you enable
[Bucket Versioning](https://docs.aws.amazon.com/AmazonS3/latest/userguide/manage-versioning-examples.html)
on the S3 bucket to allow for state recovery in the case of accidental deletions and human error.
:::

:::info
For a smooth transition to the S3 locking, please read the [dedicated section](#s3-state-locking).
:::

## Example Configuration

```hcl
terraform {
  backend "s3" {
    bucket = "mybucket"
    key    = "path/to/my/key"
    region = "us-east-1"
  }
}
```

This assumes we have a bucket created called `mybucket`. The
OpenTofu state is written to the key `path/to/my/key`.

Note that for the access credentials we recommend using a
[partial configuration](../../../language/settings/backends/configuration.mdx#partial-configuration).

### S3 Bucket Permissions

OpenTofu will need the following AWS IAM permissions on
the target backend bucket:

* `s3:ListBucket` on `arn:aws:s3:::mybucket`
* `s3:GetObject` on `arn:aws:s3:::mybucket/path/to/my/key`
* `s3:PutObject` on `arn:aws:s3:::mybucket/path/to/my/key`
* `s3:DeleteObject` on `arn:aws:s3:::mybucket/path/to/my/key`

This is seen in the following AWS IAM Statement:

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "s3:ListBucket",
      "Resource": "arn:aws:s3:::mybucket"
    },
    {
      "Effect": "Allow",
      "Action": ["s3:GetObject", "s3:PutObject", "s3:DeleteObject"],
      "Resource": "arn:aws:s3:::mybucket/path/to/my/key"
    }
  ]
}
```

:::note
AWS can control access to S3 buckets with either IAM policies
attached to users/groups/roles (like the example above) or resource policies
attached to bucket objects (which look similar but also require a `Principal` to
indicate which entity has those permissions). For more details, see Amazon's
documentation about
[S3 access control](https://docs.aws.amazon.com/AmazonS3/latest/userguide/s3-access-control.html).
:::

### DynamoDB Table Permissions

If you are using state locking, OpenTofu will need the following AWS IAM
permissions on the DynamoDB table (`arn:aws:dynamodb:::table/mytable`):

* `dynamodb:DescribeTable`
* `dynamodb:GetItem`
* `dynamodb:PutItem`
* `dynamodb:DeleteItem`

This is seen in the following AWS IAM Statement:

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:DescribeTable",
        "dynamodb:GetItem",
        "dynamodb:PutItem",
        "dynamodb:DeleteItem"
      ],
      "Resource": "arn:aws:dynamodb:*:*:table/mytable"
    }
  ]
}
```

## Data Source Configuration

To make use of the S3 remote state in another configuration, use the
[`terraform_remote_state` data source](../../../language/state/remote-state-data.mdx).

```hcl
data "terraform_remote_state" "network" {
  backend = "s3"
  config = {
    bucket = "tofu-state-prod"
    key    = "network/terraform.tfstate"
    region = "us-east-1"
  }
}
```

The `terraform_remote_state` data source will return all of the root module
outputs defined in the referenced remote state (but not any outputs from
nested modules unless they are explicitly output again in the root). An
example output might look like:

```
data.terraform_remote_state.network:
  id = 2016-10-29 01:57:59.780010914 +0000 UTC
  addresses.# = 2
  addresses.0 = 52.207.220.222
  addresses.1 = 54.196.78.166
  backend = s3
  config.% = 3
  config.bucket = tofu-state-prod
  config.key = network/terraform.tfstate
  config.region = us-east-1
  elb_address = web-elb-790251200.us-east-1.elb.amazonaws.com
  public_subnet_id = subnet-1e05dd33
```

## Configuration

This backend requires the configuration of the AWS Region and S3 state storage. Other configuration, such as enabling DynamoDB state locking, is optional.

### Credentials and Shared Configuration

:::danger Warning
We recommend using environment variables to supply credentials and other sensitive data. If you use `-backend-config` or hardcode these values directly in your configuration, OpenTofu will include these values in both the `.terraform` subdirectory and in plan files. Refer to [Credentials and Sensitive Data](../../../language/settings/backends/configuration.mdx#credentials-and-sensitive-data) for details.
:::

The following configuration is required:

* `region` - (Required) AWS Region of the S3 Bucket and DynamoDB Table (if used). This can also be sourced from the `AWS_DEFAULT_REGION` and `AWS_REGION` environment variables.

The following configuration is optional:

* `access_key` - (Optional) AWS access key. If configured, must also configure `secret_key`. This can also be sourced from the `AWS_ACCESS_KEY_ID` environment variable, AWS shared credentials file (e.g. `~/.aws/credentials`), or AWS shared configuration file (e.g. `~/.aws/config`).
* `secret_key` - (Optional) AWS access key. If configured, must also configure `access_key`. This can also be sourced from the `AWS_SECRET_ACCESS_KEY` environment variable, AWS shared credentials file (e.g. `~/.aws/credentials`), or AWS shared configuration file (e.g. `~/.aws/config`).
* `iam_endpoint` - (Optional) **Deprecated** Custom endpoint for the AWS Identity and Access Management (IAM) API. This can also be sourced from the `AWS_IAM_ENDPOINT` environment variable.
* `max_retries` - (Optional) The maximum number of times an AWS API request is retried on retryable failure. Defaults to 5.
* `retry_mode` - (Optional) Specifies how retries are attempted. Valid values are `standard` and `adaptive`. This can also be sourced from the `AWS_RETRY_MODE` environment variable.
* `profile` - (Optional) Name of AWS profile in AWS shared credentials file (e.g. `~/.aws/credentials`) or AWS shared configuration file (e.g. `~/.aws/config`) to use for credentials and/or configuration. This can also be sourced from the `AWS_PROFILE` environment variable.
* `shared_credentials_file`  - (Optional) **Deprecated** Path to the AWS shared credentials file. Defaults to `~/.aws/credentials`.
* `shared_credentials_files`  - (Optional) List of paths to AWS shared credentials files. Defaults to `~/.aws/credentials`. This can also be sourced from the `AWS_SHARED_CREDENTIALS_FILE` environment variable.
* `shared_config_files`  - (Optional) List of paths to AWS shared configuration files. Defaults to `~/.aws/config`. This can also be sourced from the `AWS_SHARED_CONFIG_FILE` environment variable.
* `skip_s3_checksum` - (Optional) Do not include checksum in the input when uploading S3 Objects.
  Useful for non AWS S3 APIs which do not support checksum validation.
* `skip_credentials_validation` - (Optional) Skip credentials validation via the STS API.
* `skip_region_validation` - (Optional) Skip validation of provided region name.
* `skip_metadata_api_check` - (Optional) Skip usage of EC2 Metadata API.
* `skip_requesting_account_id` - (Optional) Skip requesting the account ID. Useful for AWS API implementations that do not have the IAM, STS API, or metadata API.
* `sts_endpoint` - (Optional) **Deprecated** Custom endpoint for the AWS Security Token Service (STS) API. This can also be sourced from the `AWS_STS_ENDPOINT` environment variable.
* `sts_region` - (Optional) AWS region for STS. If unset, AWS will use the same region for STS as other non-STS operations.
* `token` - (Optional) Multi-Factor Authentication (MFA) token. This can also be sourced from the `AWS_SESSION_TOKEN` environment variable.
* `allowed_account_ids` (Optional): A list of permitted AWS account IDs to safeguard against accidental disruption of a live environment. This option conflicts with `forbidden_account_ids`.
* `forbidden_account_ids` (Optional): A list of prohibited AWS account IDs to prevent unintentional disruption of a live environment. This option conflicts with `allowed_account_ids`.
* `custom_ca_bundle` - File containing custom root and intermediate certificates. Can also be configured using the `AWS_CA_BUNDLE` environment variable.
* `ec2_metadata_service_endpoint` - Address of the EC2 metadata service (IMDS) endpoint to use. This can also be sourced from the `AWS_EC2_METADATA_SERVICE_ENDPOINT` environment variable.
* `ec2_metadata_service_endpoint_mode` - Mode to use in communicating with the metadata service. Valid values are `IPv4` and `IPv6`. This can also be sourced from the `AWS_EC2_METADATA_SERVICE_ENDPOINT_MODE` environment variable.
* `http_proxy` - (Optional) The address of an HTTP proxy to use when accessing the AWS API. This can also be sourced from the `HTTP_PROXY` environment variable.
* `https_proxy` - (Optional) The address of an HTTPS proxy to use when accessing the AWS API. This can also be sourced from the `HTTPS_PROXY` environment variable.
* `no_proxy` - (Optional) Comma-separated values which specify hosts that should be excluded from proxying when accessing the AWS API. This can also be sourced from the `NO_PROXY` environment variable. Find more details [here](https://cs.opensource.google/go/x/net/+/refs/tags/v0.17.0:http/httpproxy/proxy.go;l=38-50).
* `insecure` - (Optional) Explicitly allow the backend to perform "insecure" SSL requests; default is `false`.
* `use_dualstack_endpoint` - (Optional) Resolve an endpoint with DualStack capability.
* `use_fips_endpoint` - (Optional) Resolve an endpoint with FIPS capability.

#### Customizing AWS API Endpoints

The optional `endpoints` argument contains the following options:

* `s3` - (Optional) Use this to set a custom endpoint URL for the AWS S3 API. This can also be sourced from the `AWS_ENDPOINT_URL_S3` environment variable or the deprecated environment variable `AWS_S3_ENDPOINT`.
* `iam` - (Optional) Use this to set a custom endpoint URL for the AWS IAM API. This can also be sourced from the `AWS_ENDPOINT_URL_IAM` environment variable or the deprecated environment variable `AWS_IAM_ENDPOINT`.
* `sts` - (Optional) Use this to set a custom endpoint URL for the AWS STS API. This can also be sourced from the `AWS_ENDPOINT_URL_STS` environment variable or the deprecated environment variable `AWS_STS_ENDPOINT`.
* `dynamodb` - (Optional) Use this to set a custom endpoint URL for the AWS DynamoDB API. This can also be sourced from the `AWS_ENDPOINT_URL_DYNAMODB` environment variable or the deprecated environment variable `AWS_DYNAMODB_ENDPOINT`.

```hcl
terraform {
  backend "s3" {
    endpoints = {
      dynamodb = "http://localhost:4569"
      s3       = "http://localhost:4572"
    }
  }
}
```

#### Assume Role Configuration

Assuming an IAM Role is optional and can be configured in two ways.
The preferred way is to use the argument `assume_role`, as the other, the other method is deprecated.

The argument `assume_role` contains the following arguments:

* `role_arn` - (Required) The Amazon Resource Name (ARN) of the IAM Role to be assumed.
* `duration` - (Optional) Specifies the validity period for individual credentials.
  These credentials are automatically renewed, with the maximum renewal defined by the AWS account.
  The duration should be specified in the format `<hours>h<minutes>m<seconds>s`, with each unit being optional.
  For example, an hour and a half can be represented as `1h30m` or simply `90m`.
  The duration must be within the range of 15 minutes (15m) to 12 hours (12h).
* `external_id` - (Optional) An external identifier to use when assuming the role.
* `policy` - (Optional) JSON representation of an IAM Policy that further restricts permissions for the IAM Role being assumed.
* `policy_arns` - (Optional) A set of Amazon Resource Names (ARNs) for IAM Policies that further limit permissions for the assumed IAM Role.
* `session_name` - (Optional) The session name to be used when assuming the role.
* `tags` - (Optional) A map of tags to be associated with the assumed role session.
* `transitive_tag_keys` - (Optional) A set of tag keys from the assumed role session to be passed to any subsequent sessions.

The following arguments on the top level are deprecated:

* `assume_role_duration_seconds` - (Optional) Number of seconds to restrict the assume role session duration.
  Use `assume_role.duration` instead.
* `assume_role_policy` - (Optional) IAM Policy JSON describing further restricting permissions for the IAM Role being assumed.
  Use `assume_role.policy` instead.
* `assume_role_policy_arns` - (Optional) Set of Amazon Resource Names (ARNs) of IAM Policies describing further restricting permissions for the IAM Role being assumed.
  Use `assume_role.policy_arns` instead.
* `assume_role_tags` - (Optional) Map of assume role session tags.
  Use `assume_role.tags` instead.
* `assume_role_transitive_tag_keys` - (Optional) Set of assume role session tag keys to pass to any subsequent sessions.
  Use `assume_role.transitive_tag_keys` instead.
* `external_id` - (Optional) External identifier to use when assuming the role.
  Use `assume_role.external_id` instead.
* `role_arn` - (Optional) Amazon Resource Name (ARN) of the IAM Role to assume.
  Use `assume_role.role_arn` instead.
* `session_name` - (Optional) Session name to use when assuming the role.
  Use `assume_role.session_name` instead.

```hcl
terraform {
  backend "s3" {
    bucket = "mybucket"
    key    = "my/key.tfstate"
    region = "us-east-1"
    assume_role = {
      role_arn = "arn:aws:iam::ACCOUNT-ID:role/Opentofu"
    }
  }
}
```

#### Assume Role With Web Identity Configuration

The following `assume_role_with_web_identity` configuration block is optional:

* `role_arn` - (Required) Amazon Resource Name (ARN) of the IAM Role to assume.
Can also be set with the `AWS_ROLE_ARN` environment variable.
* `duration` - (Optional) The duration individual credentials will be valid.
Credentials are automatically renewed up to the maximum defined by the AWS account.
Specified using the format `<hours>h<minutes>m<seconds>s` with any unit being optional.
For example, an hour and a half can be specified as `1h30m` or `90m`.
Must be between 15 minutes (15m) and 12 hours (12h).
* `policy` - (Optional) IAM Policy JSON describing further restricting permissions for the IAM Role being assumed.
* `policy_arns` - (Optional) Set of Amazon Resource Names (ARNs) of IAM Policies describing further restricting permissions for the IAM Role being assumed.
* `session_name` - (Optional) Session name to use when assuming the role.
Can also be set with the `AWS_ROLE_SESSION_NAME` environment variable.
* `web_identity_token` - (Optional) The value of a web identity token from an OpenID Connect (OIDC) or OAuth provider.
One of `web_identity_token` or `web_identity_token_file` is required.
* `web_identity_token_file` - (Optional) File containing a web identity token from an OpenID Connect (OIDC) or OAuth provider.
One of `web_identity_token_file` or `web_identity_token` is required.
Can also be set with the `AWS_WEB_IDENTITY_TOKEN_FILE` environment variable.

```hcl
terraform {
  backend "s3" {
    bucket = "mybucket"
    key    = "my/key.tfstate"
    region = "us-east-1"

    assume_role_with_web_identity = {
      role_arn           = "arn:aws:iam::ACCOUNT-ID:role/Opentofu"
      web_identity_token = "<token value>"
    }
  }
}
```

It's possible to constrain the assumed role by providing a policy.

```hcl
terraform {
  backend "s3" {
    bucket = "mybucket"
    key    = "my/key.tfstate"
    region = "us-east-1"

    assume_role_with_web_identity = {
      role_arn           = "arn:aws:iam::ACCOUNT-ID:role/Opentofu"
      web_identity_token = "<token value>"
      policy             = <<-JSON
			{
				"Version": "2012-10-17",
				"Statement": [
					{
						"Effect": "Allow",
						"Action": "s3:*",
						"Resource": [
							"arn:aws:s3:::mybucket/*",
							"arn:aws:s3:::mybucket"
						]
					}
				]
			}
			JSON
    }
  }
}
```

### S3 State Storage

The following configuration is required:

* `bucket` - (Required) Name of the S3 Bucket.
* `key` - (Required) Path to the state file inside the S3 Bucket. When using a non-default [workspace](../../../language/state/workspaces.mdx), the state path will be `/workspace_key_prefix/workspace_name/key` (see also the `workspace_key_prefix` configuration).

The following configuration is optional:

* `acl` - (Optional) [Canned ACL](https://docs.aws.amazon.com/AmazonS3/latest/userguide/acl-overview.html#canned-acl) to be applied to the state file.
* `encrypt` - (Optional) Enable [server side encryption](https://docs.aws.amazon.com/AmazonS3/latest/userguide/UsingServerSideEncryption.html) of the state file.
* `endpoint` - (Optional) **Deprecated** Custom endpoint for the AWS S3 API. This can also be sourced from the `AWS_S3_ENDPOINT` environment variable.
* `force_path_style` - (Optional) **Deprecated** Enable path-style S3 URLs (`https://<HOST>/<BUCKET>` instead of `https://<BUCKET>.<HOST>`). Use `use_path_style` instead.
* `use_path_style` - (Optional) Enable path-style S3 URLs (`https://<HOST>/<BUCKET>` instead of `https://<BUCKET>.<HOST>`).
* `kms_key_id` - (Optional) Amazon Resource Name (ARN) of a Key Management Service (KMS) Key to use for encrypting the state. Note that if this value is specified, OpenTofu will need `kms:Encrypt`, `kms:Decrypt` and `kms:GenerateDataKey` permissions on this KMS key.
* `sse_customer_key` - (Optional) The key to use for encrypting state with [Server-Side Encryption with Customer-Provided Keys (SSE-C)](https://docs.aws.amazon.com/AmazonS3/latest/userguide/ServerSideEncryptionCustomerKeys.html). This is the base64-encoded value of the key, which must decode to 256 bits. This can also be sourced from the `AWS_SSE_CUSTOMER_KEY` environment variable, which is recommended due to the sensitivity of the value. Setting it inside an OpenTofu file will cause it to be persisted to disk in `terraform.tfstate`.
* `workspace_key_prefix` - (Optional) Prefix applied to the state path inside the bucket. This is only relevant when using a non-default workspace. Defaults to `env:`.

### DynamoDB State Locking

The following configuration is optional:

* `dynamodb_endpoint` - (Optional) **Deprecated** Custom endpoint for the AWS DynamoDB API. This can also be sourced from the `AWS_DYNAMODB_ENDPOINT` environment variable.
* `dynamodb_table` - (Optional) Name of DynamoDB Table to use for state locking and consistency. The table must have a partition key named `LockID` with type of `String`. If not configured, state locking will be disabled.

### S3 State Locking

* `use_lockfile` - (Optional) Enable locking directly into the configured bucket for the state.

To migrate from DynamoDB to S3 locking, the following steps can be followed:
1. The new attribute `use_lockfile=true` can be added alongside `dynamodb_table`:
   * With both attributes specified, OpenTofu will try to acquire the lock first in S3 and if successful, will try to acquire the lock in DynamoDB. In this case, the lock will be considered acquired only when both (S3 and DynamoDB) locks were acquired successfully.
   * Later, after a baking period with both locking mechanisms enabled, if no issues encountered, remove the `dynamodb_table` attribute. Now, you are solely on the S3 locking.
   * **Info:** Keeping both locking mechanisms enabled, ensures that nobody will acquire the lock regardless of having or not the latest configuration.
2. The new attribute `use_lockfile=true` can be added and `dynamodb_table` removed:
   * This will switch from DynamoDB to S3 locking. **Caution:** when the updated configuration is executed from multiple places (multiple machines, pipelines on PRs, etc), you might get into issues where one outdated copy of the configuration is using DynamoDB locking and the one updated is using S3 locking. This could end up in concurrent access on the same state file.
   * Once the state is updated by using this approach, the state digest that OpenTofu was storing in DynamoDB (for data consistency checks) will get stale. If you wish to go back to DynamoDB locking, **the old digest needs to be cleaned up manually**.

:::note
Remember, any changes to the `backend` block will require to run `tofu init -reconfigure`.
:::

:::note
As mentioned in the beginning of this page, OpenTofu recommends to have versioning enabled on the S3 bucket where state file(s) are stored.
By setting `use_lockfile=true`, acquiring and releasing locks will add a good amount of writes and reads to the bucket.
Therefore, for a versioning-enabled bucket, the number of versions for that object could grow significantly.
Even though the cost should be negligible for the locking objects, a lifecycle configuration of the S3 bucket to limit the number of versions of an object would be advised.
:::

When it comes to the workspace usage, the S3 locking will behave normally, storing the lock file right next to its related state object.

## Multi-account AWS Architecture

A common architectural pattern is for an organization to use a number of
separate AWS accounts to isolate different teams and environments. For example,
a "staging" system will often be deployed into a separate AWS account than
its corresponding "production" system, to minimize the risk of the staging
environment affecting production infrastructure, whether via rate limiting,
misconfigured access controls, or other unintended interactions.

The S3 backend can be used in a number of different ways that make different
tradeoffs between convenience, security, and isolation in such an organization.
This section describes one such approach that aims to find a good compromise
between these tradeoffs, allowing use of
[OpenTofu's workspaces feature](../../../language/state/workspaces.mdx) to switch
conveniently between multiple isolated deployments of the same configuration.

Use this section as a starting-point for your approach, but note that
you will probably need to make adjustments for the unique standards and
regulations that apply to your organization. You will also need to make some
adjustments to this approach to account for _existing_ practices within your
organization, if for example other tools have previously been used to manage
infrastructure.

OpenTofu is an administrative tool that manages your infrastructure, and so
ideally the infrastructure that is used by OpenTofu should exist outside of
the infrastructure that OpenTofu manages. This can be achieved by creating a
separate _administrative_ AWS account which contains the user accounts used by
human operators and any infrastructure and tools used to manage the other
accounts. Isolating shared administrative tools from your main environments
has a number of advantages, such as avoiding accidentally damaging the
administrative infrastructure while changing the target infrastructure, and
reducing the risk that an attacker might abuse production infrastructure to
gain access to the (usually more privileged) administrative infrastructure.

### Administrative Account Setup

Your administrative AWS account will contain at least the following items:

* One or more [IAM user](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_users.html)
  for system administrators that will log in to maintain infrastructure in
  the other accounts.
* Optionally, one or more [IAM groups](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_groups.html)
  to differentiate between different groups of users that have different
  levels of access to the other AWS accounts.
* An [S3 bucket](https://docs.aws.amazon.com/AmazonS3/latest/userguide/UsingBucket.html)
  that will contain the OpenTofu state files for each workspace.
* A [DynamoDB table](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.CoreComponents.html#HowItWorks.CoreComponents.TablesItemsAttributes)
  that will be used for locking to prevent concurrent operations on a single
  workspace.

Provide the S3 bucket name and DynamoDB table name to OpenTofu within the
S3 backend configuration using the `bucket` and `dynamodb_table` arguments
respectively, and configure a suitable `workspace_key_prefix` to contain
the states of the various workspaces that will subsequently be created for
this configuration.

### Environment Account Setup

For the sake of this section, the term "environment account" refers to one
of the accounts whose contents are managed by OpenTofu, separate from the
administrative account described above.

Your environment accounts will eventually contain your own product-specific
infrastructure. Along with this it must contain one or more
[IAM roles](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles.html)
that grant sufficient access for OpenTofu to perform the desired management
tasks.

### Delegating Access

Each Administrator will run OpenTofu using credentials for their IAM user
in the administrative account.
[IAM Role Delegation](https://docs.aws.amazon.com/IAM/latest/UserGuide/tutorial_cross-account-with-roles.html)
is used to grant these users access to the roles created in each environment
account.

Full details on role delegation are covered in the AWS documentation linked
above. The most important details are:

* Each role's _Assume Role Policy_ must grant access to the administrative AWS
  account, which creates a trust relationship with the administrative AWS
  account so that its users may assume the role.
* The users or groups within the administrative account must also have a
  policy that creates the converse relationship, allowing these users or groups
  to assume that role.

Since the purpose of the administrative account is only to host tools for
managing other accounts, it is useful to give the administrative accounts
restricted access only to the specific operations needed to assume the
environment account role and access the OpenTofu state. By blocking all
other access, you remove the risk that user error will lead to staging or
production resources being created in the administrative account by mistake.

When configuring OpenTofu, use either environment variables or the standard
credentials file `~/.aws/credentials` to provide the administrator user's
IAM credentials within the administrative account to both the S3 backend _and_
to OpenTofu's AWS provider.

Use conditional configuration to pass a different `assume_role` value to
the AWS provider depending on the selected workspace. For example:

```hcl
variable "workspace_iam_roles" {
  default = {
    staging    = "arn:aws:iam::STAGING-ACCOUNT-ID:role/OpenTofu"
    production = "arn:aws:iam::PRODUCTION-ACCOUNT-ID:role/OpenTofu"
  }
}

provider "aws" {
  # No credentials explicitly set here because they come from either the
  # environment or the global credentials file.

  assume_role {
    role_arn = "${var.workspace_iam_roles[terraform.workspace]}"
  }
}
```

If workspace IAM roles are centrally managed and shared across many separate
OpenTofu configurations, the role ARNs could also be obtained via a data
source such as [`terraform_remote_state`](../../../language/state/remote-state-data.mdx)
to avoid repeating these values.

### Creating and Selecting Workspaces

With the necessary objects created and the backend configured, run
`tofu init` to initialize the backend and establish an initial workspace
called "default". This workspace will not be used, but is created automatically
by OpenTofu as a convenience for users who are not using the workspaces
feature.

Create a workspace corresponding to each key given in the `workspace_iam_roles`
variable value above:

```
$ tofu workspace new staging
Created and switched to workspace "staging"!

...

$ tofu workspace new production
Created and switched to workspace "production"!

...
```

Due to the `assume_role` setting in the AWS provider configuration, any
management operations for AWS resources will be performed via the configured
role in the appropriate environment AWS account. The backend operations, such
as reading and writing the state from S3, will be performed directly as the
administrator's own user within the administrative account.

```
$ tofu workspace select staging
$ tofu apply
...
```

### Running OpenTofu in Amazon EC2

Teams that make extensive use of OpenTofu for infrastructure management
often run OpenTofu in automation
to ensure a consistent operating environment and to limit access to the
various secrets and other sensitive information that OpenTofu configurations
tend to require.

When running OpenTofu in an automation tool running on an Amazon EC2 instance,
consider running this instance in the administrative account and using an
[instance profile](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_use_switch-role-ec2_instance-profiles.html)
in place of the various administrator IAM users suggested above. An IAM
instance profile can also be granted cross-account delegation access via
an IAM policy, giving this instance the access it needs to run OpenTofu.

To isolate access to different environment accounts, use a separate EC2
instance for each target account so that its access can be limited only to
the single account.

Similar approaches can be taken with equivalent features in other AWS compute
services, such as ECS.

### Protecting Access to Workspace State

In a simple implementation of the pattern described in the prior sections,
all users have access to read and write states for all workspaces. In many
cases it is desirable to apply more precise access constraints to the
OpenTofu state objects in S3, so that for example only trusted administrators
are allowed to modify the production state, or to control _reading_ of a state
that contains sensitive information.

Amazon S3 supports fine-grained access control on a per-object-path basis
using IAM policy. A full description of S3's access control mechanism is
beyond the scope of this guide, but an example IAM policy granting access
to only a single state object within an S3 bucket is shown below:

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "s3:ListBucket",
      "Resource": "arn:aws:s3:::myorg-tofu-states"
    },
    {
      "Effect": "Allow",
      "Action": ["s3:GetObject", "s3:PutObject"],
      "Resource": "arn:aws:s3:::myorg-tofu-states/myapp/production/tfstate"
    }
  ]
}
```

It is also possible to apply fine-grained access control to the DynamoDB
table used for locking. When OpenTofu puts the state lock in place during `tofu plan`, it stores the full state file as a document and sets the s3 object key as the partition key for the document. After the state lock is released, OpenTofu places a digest of the updated state file in DynamoDB. The key is similar to the one for the original state file, but is suffixed with `-md5`.

The example below shows a simple IAM policy that allows the backend operations role to perform these operations:

```json
{
  "Version": "2012-10-17",
  "Statement": [
      {
        "Effect" : "Allow",
        "Action" : [
          "dynamodb:DeleteItem",
          "dynamodb:GetItem",
          "dynamodb:PutItem",
          "dynamodb:Query",
          "dynamodb:UpdateItem"
        ],
        "Resource" : ["arn:aws:dynamodb:*:*:table/myorg-state-lock-table"],
        "Condition" : {
          "ForAllValues:StringEquals" : {
            "dynamodb:LeadingKeys" : [
              "myorg-tofu-states/myapp/production/tfstate", // during a state lock the full state file is stored with this key
              "myorg-tofu-states/myapp/production/tfstate-md5" // after the lock is released a hash of the statefile's contents are stored with this key
            ]
          }
        }
      }
  ]
}
```

Refer to the [AWS documentation on DynamoDB fine-grained locking](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/specifying-conditions.html) for more details.

### Configuring Custom User-Agent Information

Note this feature is optional.

By default, the underlying AWS client used by the OpenTofu AWS Provider creates requests with User-Agent headers including information about OpenTofu and AWS Go SDK versions. To provide additional information in the User-Agent headers, the `TF_APPEND_USER_AGENT` environment variable can be set and its value will be directly added to HTTP requests. e.g.

```sh
$ export TF_APPEND_USER_AGENT="JenkinsAgent/i-12345678 BuildID/1234 (Optional Extra Information)"
```
