opentf/website/docs/language/settings/backends/cos.mdx

---
sidebar_label: cos
description: >-
  OpenTofu can store the state remotely, making it easier to version and work
  with in a team.
---

# Backend Type: COS

Stores the state as an object in a configurable prefix in a given bucket on [Tencent Cloud Object Storage](https://intl.cloud.tencent.com/product/cos) (COS).

This backend supports [state locking](../../../language/state/locking.mdx). Storing your state in a COS bucket requires the following permissions:

- `CreateTag`, `DeleteTag`, and `DescribeTags` on the tag key `tencentcloud-terraform-lock`
- `Put`, `Get`, and `Delete` files for the specified bucket's prefix

:::warning
It is highly recommended that you enable [Object Versioning](https://intl.cloud.tencent.com/document/product/436/19883)
on the COS bucket to allow for state recovery in the case of accidental deletions and human error.
:::

## Example Configuration

```hcl
terraform {
  backend "cos" {
    region = "ap-guangzhou"
    bucket = "bucket-for-tofu-state-1258798060"
    prefix = "tofu/state"
  }
}
```

This assumes we have a [COS Bucket](https://registry.terraform.io/providers/tencentcloudstack/tencentcloud/latest/docs/resources/cos_bucket) created named `bucket-for-tofu-state-1258798060`,
OpenTofu state will be written into the file `tofu/state/terraform.tfstate`.

## Data Source Configuration

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

```hcl
data "terraform_remote_state" "foo" {
  backend = "cos"

  config = {
    region = "ap-guangzhou"
    bucket = "bucket-for-tofu-state-1258798060"
    prefix = "tofu/state"
  }
}
```

## Configuration Variables

:::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 options or environment variables are supported:

- `secret_id` - (Optional) Secret id of Tencent Cloud. It supports environment variables `TENCENTCLOUD_SECRET_ID`.
- `secret_key` - (Optional) Secret key of Tencent Cloud. It supports environment variables `TENCENTCLOUD_SECRET_KEY`.
- `security_token` - (Optional) TencentCloud Security Token of temporary access credentials. It supports environment variables `TENCENTCLOUD_SECURITY_TOKEN`.
- `region` - (Optional) The region of the COS bucket. It supports environment variables `TENCENTCLOUD_REGION`.
- `bucket` - (Required) The name of the COS bucket. You shall manually create it first.
- `prefix` - (Optional) The directory for saving the state file in bucket. Default to "env:".
- `key` - (Optional) The path for saving the state file in bucket. Defaults to `terraform.tfstate`.
- `encrypt` - (Optional) Whether to enable server side encryption of the state file. If it is true, COS will use 'AES256' encryption algorithm to encrypt state file.
- `acl` - (Optional) Object ACL to be applied to the state file, allows `private` and `public-read`. Defaults to `private`.
- `accelerate` - (Optional) Whether to enable global Acceleration. Defaults to `false`.

### Assume Role
If provided with an assume role, OpenTofu will attempt to assume this role using the supplied credentials.
Assume role can be provided by adding an `assume_role` block in the cos backend block.

- `assume_role` - (Optional) The `assume_role` block. If provided, OpenTofu will attempt to assume this role using the supplied credentials.

The details of `assume_role` block as following:
- `role_arn` - (Required) The ARN of the role to assume. It can be sourced from the `TENCENTCLOUD_ASSUME_ROLE_ARN`.
- `session_name` - (Required) The session name to use when making the AssumeRole call. It can be sourced from the `TENCENTCLOUD_ASSUME_ROLE_SESSION_NAME`.
- `session_duration` - (Required) The duration of the session when making the AssumeRole call. Its value ranges from 0 to 43200(seconds), and default is 7200 seconds. It can be sourced from the `TENCENTCLOUD_ASSUME_ROLE_SESSION_DURATION`.
- `policy` - (Optional) A more restrictive policy when making the AssumeRole call. Its content must not contains `principal` elements. Notice: more syntax references, please refer to: [policies syntax logic](https://intl.cloud.tencent.com/document/product/598/10603).

Usage:

```hcl
terraform {
  backend "cos" {
    region = "ap-guangzhou"
    bucket = "bucket-for-tofu-state-{appid}"
    prefix = "tofu/state"
    assume_role {
      role_arn = "qcs::cam::uin/xxx:roleName/yyy"
      session_name = "my-session-name"
      session_duration = 3600
    }
  }
}
```

In addition, these `assume_role` configurations can also be provided by environment variables.

Usage:

```shell
$ export TENCENTCLOUD_SECRET_ID="my-secret-id"
$ export TENCENTCLOUD_SECRET_KEY="my-secret-key"
$ export TENCENTCLOUD_REGION="ap-guangzhou"
$ export TENCENTCLOUD_ASSUME_ROLE_ARN="qcs::cam::uin/xxx:roleName/yyy"
$ export TENCENTCLOUD_ASSUME_ROLE_SESSION_NAME="my-session-name"
$ export TENCENTCLOUD_ASSUME_ROLE_SESSION_DURATION=3600
$ tofu plan
```