This component is responsible for provisioning an S3 Bucket and DynamoDB table that follow security best practices for usage as a Terraform backend. It also creates IAM roles for access to the Terraform backend.

Once the initial S3 backend is configured, this component can create additional backends, allowing you to segregate them and control access to each backend separately. This may be desirable because any secret or sensitive information (such as generated passwords) that Terraform has access to gets stored in the Terraform state backend S3 bucket, so you may wish to restrict who can read the production Terraform state backend S3 bucket. However, perhaps counter-intuitively, all Terraform users require read access to the most sensitive accounts, such as root and audit, in order to read security configuration information, so careful planning is required when architecting backend splits.

Prerequisites

Tip

Part of cold start, so it has to initially be run with SuperAdmin, multiple times: to create the S3 bucket and then to move the state into it. Follow the guide here to get started.

• This component assumes you are using the aws-teams and aws-team-roles components.
• Before the account and account-map components are deployed for the first time, you'll want to run this component with access_roles_enabled set to false to prevent errors due to missing IAM Role ARNs. This will enable only enough access to the Terraform state for you to finish provisioning accounts and roles. After those components have been deployed, you will want to run this component again with access_roles_enabled set to true to provide the complete access as configured in the stacks.

Access Control

For each backend, this module will create an IAM role with read/write access and, optionally, an IAM role with read-only access. You can configure who is allowed to assume these roles.

• While read/write access is required for terraform apply, the created role only grants read/write access to the Terraform state, it does not grant permission to create/modify/destroy AWS resources.

• Similarly, while the read-only role prohibits making changes to the Terraform state, it does not prevent anyone from making changes to AWS resources using a different role.

• Many Cloud Posse components store information about resources they create in the Terraform state via their outputs, and many other components read this information from the Terraform state backend via the CloudPosse remote-state module and use it as part of their configuration. For example, the account-map component exists solely for the purpose of organizing information about the created AWS accounts and storing it in its Terraform state, making it available via remote-state. This means that you if you are going to restrict access to some backends, you need to carefully orchestrate what is stored there and ensure that you are not storing information a component needs in a backend it will not have access to. Typically, information in the most sensitive accounts, such as root, audit, and security, is nevertheless needed by every account, for example to know where to send audit logs, so it is not obvious and can be counter-intuitive which accounts need access to which backends. Plan carefully.

• Atmos provides separate configuration for Terraform state access via the backend and remote_state_backend settings. Always configure the backend setting with a role that has read/write access (and override that setting to be null for components deployed by SuperAdmin). If a read-only role is available (only helpful if you have more than one backend), use that role in remote_state_backend.s3.role_arn. Otherwise, use the read/write role in remote_state_backend.s3.role_arn, to ensure that all components can read the Terraform state, even if backend.s3.role_arn is set to null, as it is with a few critical components meant to be deployed by SuperAdmin.

• Note that the "read-only" in the "read-only role" refers solely to the S3 bucket that stores the backend data. That role still has read/write access to the DynamoDB table, which is desirable so that users restricted to the read-only role can still perform drift detection by running terraform plan. The DynamoDB table only stores checksums and mutual-exclusion lock information, so it is not considered sensitive. The worst a malicious user could do would be to corrupt the table and cause a denial-of-service (DoS) for Terraform, but such DoS would only affect making changes to the infrastructure, it would not affect the operation of the existing infrastructure, so it is an ineffective and therefore unlikely vector of attack. (Also note that the entire DynamoDB table is optional and can be deleted entirely; Terraform will repopulate it as new activity takes place.)

• For convenience, the component automatically grants access to the backend to the user deploying it. This is helpful because it allows that user, presumably SuperAdmin, to deploy the normal components that expect the user does not have direct access to Terraform state, without requiring custom configuration. However, you may want to explicitly grant SuperAdmin access to the backend in the allowed_principal_arns configuration, to ensure that SuperAdmin can always access the backend, even if the component is later updated by the root-admin role.

Quotas

When allowing access to both SAML and AWS SSO users, the trust policy for the IAM roles created by this component can exceed the default 2048 character limit. If you encounter this error, you can increase the limit by requesting a quota increase here. Note that this is the IAM limit on "The maximum number of characters in an IAM role trust policy" and it must be configured in the us-east-1 region, regardless of what region you are deploying to. Normally 3072 characters is sufficient, and is recommended so that you still have room to expand the trust policy in the future while perhaps considering how to reduce its size.

Usage

Stack Level: Regional (because DynamoDB is region-specific), but deploy only in a single region and only in the root account Deployment: Must be deployed by SuperAdmin using atmos CLI

This component configures the shared Terraform backend, and as such is the first component that must be deployed, since all other components depend on it. In fact, this component even depends on itself, so special deployment procedures are needed for the initial deployment (documented in the "Cold Start" procedures).

Here's an example snippet for how to use this component.

terraform:
  tfstate-backend:
    backend:
      s3:
        role_arn: null
    settings:
      spacelift:
        workspace_enabled: false
    vars:
      enable_server_side_encryption: true
      enabled: true
      force_destroy: false
      name: tfstate
      prevent_unencrypted_uploads: true
      access_roles:
        default: &tfstate-access-template
          write_enabled: true
          allowed_roles:
            core-identity: ["devops", "developers", "managers", "spacelift"]
            core-root: ["admin"]
          denied_roles: {}
          allowed_permission_sets:
            core-identity: ["AdministratorAccess"]
          denied_permission_sets: {}
          allowed_principal_arns: []
          denied_principal_arns: []

Requirements

Name	Version
terraform	>= 1.0.0
aws	>= 4.9.0
awsutils	>= 0.16.0

Providers

Name	Version
aws	>= 4.9.0
awsutils	>= 0.16.0

Modules

Name	Source	Version
assume_role	../account-map/modules/team-assume-role-policy	n/a
label	cloudposse/label/null	0.25.0
tfstate_backend	cloudposse/tfstate-backend/aws	1.5.0
this	cloudposse/label/null	0.25.0

Resources

Name	Type
aws_iam_role.default	resource
aws_arn.cold_start_access	data source
aws_iam_policy_document.cold_start_assume_role	data source
aws_iam_policy_document.tfstate	data source
aws_partition.current	data source
awsutils_caller_identity.current	data source

Inputs

Name	Description	Type	Default	Required
access_roles	Map of access roles to create (key is role name, use "default" for same as component). See iam-assume-role-policy module for details.	map(object({ write_enabled = bool allowed_roles = map(list(string)) denied_roles = map(list(string)) allowed_principal_arns = list(string) denied_principal_arns = list(string) allowed_permission_sets = map(list(string)) denied_permission_sets = map(list(string)) }))	{}	no
access_roles_enabled	Enable access roles to be assumed. Set false for cold start (before account-map has been created), because the role to ARN mapping has not yet been created. Note that the current caller and any allowed_principal_arns will always be allowed to assume the role.	bool	true	no
additional_tag_map	Additional key-value pairs to add to each map in tags_as_list_of_maps. Not added to tags or id. This is for some rare cases where resources want additional configuration of tags and therefore take a list of maps with tag key, value, and additional configuration.	map(string)	{}	no
attributes	ID element. Additional attributes (e.g. workers or cluster) to add to id, in the order they appear in the list. New attributes are appended to the end of the list. The elements of the list are joined by the delimiter and treated as a single ID element.	list(string)	[]	no
context	Single object for setting entire context at once. See description of individual variables for details. Leave string and numeric variables as null to use default value. Individual variable settings (non-null) override settings in context object, except for attributes, tags, and additional_tag_map, which are merged.	any	{ "additional_tag_map": {}, "attributes": [], "delimiter": null, "descriptor_formats": {}, "enabled": true, "environment": null, "id_length_limit": null, "label_key_case": null, "label_order": [], "label_value_case": null, "labels_as_tags": [ "unset" ], "name": null, "namespace": null, "regex_replace_chars": null, "stage": null, "tags": {}, "tenant": null }	no
delimiter	Delimiter to be used between ID elements. Defaults to - (hyphen). Set to "" to use no delimiter at all.	string	null	no
descriptor_formats	Describe additional descriptors to be output in the descriptors output map. Map of maps. Keys are names of descriptors. Values are maps of the form {<br/> format = string<br/> labels = list(string)<br/>} (Type is any so the map values can later be enhanced to provide additional options.) format is a Terraform format string to be passed to the format() function. labels is a list of labels, in order, to pass to format() function. Label values will be normalized before being passed to format() so they will be identical to how they appear in id. Default is {} (descriptors output will be empty).	any	{}	no
enable_point_in_time_recovery	Enable DynamoDB point-in-time recovery	bool	true	no
enable_server_side_encryption	Enable DynamoDB and S3 server-side encryption	bool	true	no
enabled	Set to false to prevent the module from creating any resources	bool	null	no
environment	ID element. Usually used for region e.g. 'uw2', 'us-west-2', OR role 'prod', 'staging', 'dev', 'UAT'	string	null	no
force_destroy	A boolean that indicates the terraform state S3 bucket can be destroyed even if it contains objects. These objects are not recoverable.	bool	false	no
id_length_limit	Limit id to this many characters (minimum 6). Set to 0 for unlimited length. Set to null for keep the existing setting, which defaults to 0. Does not affect id_full.	number	null	no
label_key_case	Controls the letter case of the tags keys (label names) for tags generated by this module. Does not affect keys of tags passed in via the tags input. Possible values: lower, title, upper. Default value: title.	string	null	no
label_order	The order in which the labels (ID elements) appear in the id. Defaults to ["namespace", "environment", "stage", "name", "attributes"]. You can omit any of the 6 labels ("tenant" is the 6th), but at least one must be present.	list(string)	null	no
label_value_case	Controls the letter case of ID elements (labels) as included in id, set as tag values, and output by this module individually. Does not affect values of tags passed in via the tags input. Possible values: lower, title, upper and none (no transformation). Set this to title and set delimiter to "" to yield Pascal Case IDs. Default value: lower.	string	null	no
labels_as_tags	Set of labels (ID elements) to include as tags in the tags output. Default is to include all labels. Tags with empty values will not be included in the tags output. Set to [] to suppress all generated tags. Notes: The value of the name tag, if included, will be the id, not the name. Unlike other null-label inputs, the initial setting of labels_as_tags cannot be changed in later chained modules. Attempts to change it will be silently ignored.	set(string)	[ "default" ]	no
name	ID element. Usually the component or solution name, e.g. 'app' or 'jenkins'. This is the only ID element not also included as a tag. The "name" tag is set to the full id string. There is no tag with the value of the name input.	string	null	no
namespace	ID element. Usually an abbreviation of your organization name, e.g. 'eg' or 'cp', to help ensure generated IDs are globally unique	string	null	no
prevent_unencrypted_uploads	Prevent uploads of unencrypted objects to S3	bool	true	no
regex_replace_chars	Terraform regular expression (regex) string. Characters matching the regex will be removed from the ID elements. If not set, "/[^a-zA-Z0-9-]/" is used to remove all characters other than hyphens, letters and digits.	string	null	no
region	AWS Region	string	n/a	yes
stage	ID element. Usually used to indicate role, e.g. 'prod', 'staging', 'source', 'build', 'test', 'deploy', 'release'	string	null	no
tags	Additional tags (e.g. {'BusinessUnit': 'XYZ'}). Neither the tag keys nor the tag values will be modified by this module.	map(string)	{}	no
tenant	ID element _(Rarely used, not included by default)_. A customer identifier, indicating who this instance of a resource is for	string	null	no

Outputs

Name	Description
tfstate_backend_access_role_arns	IAM Role ARNs for accessing the Terraform State Backend
tfstate_backend_dynamodb_table_arn	Terraform state DynamoDB table ARN
tfstate_backend_dynamodb_table_id	Terraform state DynamoDB table ID
tfstate_backend_dynamodb_table_name	Terraform state DynamoDB table name
tfstate_backend_s3_bucket_arn	Terraform state S3 bucket ARN
tfstate_backend_s3_bucket_domain_name	Terraform state S3 bucket domain name
tfstate_backend_s3_bucket_id	Terraform state S3 bucket ID

References

• cloudposse/terraform-aws-components - Cloud Posse's upstream component

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Related Projects

Check out these related projects.

• Cloud Posse Terraform Modules - Our collection of reusable Terraform modules used by our reference architectures.
• Atmos - Atmos is like docker-compose but for your infrastructure

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