Setting up Parameter Store
Before setting up parameters in Parameter Store, configure AWS Identity and Access Management (IAM) policies that provide principals in your account with permission to perform the actions you specify.
In this section, you learn how to manually configure these policies using the IAM console, and how to assign them to users and user groups. You can also create and assign policies to control which parameter actions can be run on a managed node.
This section also explains how to create Amazon EventBridge rules that let you receive notifications about changes to Systems Manager parameters. You can use EventBridge rules to invoke other actions in AWS based on changes in Parameter Store.
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Managing access to Parameter Store parameters using IAM policies
The IAM principal that accesses AWS Systems Manager parameters must have permission to perform the required SSM actions. The principal can be an IAM user, IAM role, Amazon EC2 instance profile, Lambda execution role, Amazon ECS task role, CodeBuild service role, or another AWS service role.
The following table describes the IAM permissions required for different Parameter Store actions.
| Action | Required IAM privilege | Reference information |
|---|---|---|
| Create or update a parameter | ssm:PutParameter |
PutParameter |
| Retrieve one parameter | ssm:GetParameter |
GetParameter |
| Retrieve multiple named parameters | ssm:GetParameters |
GetParameters |
| Retrieve parameters under a path | ssm:GetParametersByPath |
GetParametersByPath |
| View parameter metadata | ssm:DescribeParameters |
DescribeParameters |
| View parameter version history | ssm:GetParameterHistory |
GetParameterHistory |
| Delete one parameter | ssm:DeleteParameter |
DeleteParameter |
| Delete multiple parameters | ssm:DeleteParameters |
DeleteParameters |
When using IAM policies to grant access to Systems Manager parameters, we recommend
that you create and use restrictive IAM
policies. For example, the following policy allows a principal to call the DescribeParameters and GetParameters API operations for a limited set of resources. The principal can get information about and use all parameters that begin with
prod-*.
Note
The preceding policy allows ssm:GetParameters but not the other
retrieval actions. Parameter Store authorizes each retrieval operation against its own
IAM action, so allowing or denying one action doesn't affect the others. Before
you rely on a policy to restrict which parameters a principal can read, see
How Parameter Store authorizes parameter retrieval and Restricting access to specific parameters and paths.
Important
Parameter Store authorizes the GetParametersByPath operation against the path
that you specify in the request, not against each parameter that the operation returns.
A principal who is allowed to call GetParametersByPath for the path
/a receives every parameter under that path, including
/a/b. This is true even if the same policy explicitly denies
access to /a/b for other actions.
To prevent a parameter from being returned by GetParametersByPath, deny
the ssm:GetParametersByPath action on every ancestor path that could
include the parameter in its results. For example, to prevent
/a/b from being returned, deny
ssm:GetParametersByPath for both /a and
/.
For trusted administrators, you can provide access to all Systems Manager parameter API
operations by using a policy similar to the following example. This policy gives the
user full access to all production parameters that begin with
dbserver-prod-*.
Denying permissions
Each API is unique and has distinct operations and permissions that you can allow or deny individually. An explicit deny in any policy overrides the allow.
Important
Because each operation is authorized against its own IAM action, denying
a single action doesn't prevent a principal from retrieving the same
parameter through another operation. For example, denying
ssm:GetParameter alone has no effect on
ssm:GetParameters, ssm:GetParameterHistory, or
ssm:GetParametersByPath. Always deny every action that can
return the value. For a complete description of this behavior, see How Parameter Store authorizes parameter retrieval.
Note
The default AWS Key Management Service (AWS KMS) key has Decrypt permission for
all IAM principals within the AWS account. If you want different
access levels to SecureString parameters in your account, we
don't recommend that you use the default key. Restricting
kms:Decrypt on a customer managed key prevents decryption of a
SecureString value through any retrieval operation. For
more information, see Restricting decryption of SecureString parameter values.
All four retrieval action names begin with GetParameter, so the
single entry ssm:GetParameter* covers
ssm:GetParameter, ssm:GetParameters,
ssm:GetParameterHistory, and
ssm:GetParametersByPath. The following example uses this pattern to
deny all four actions for all parameters beginning with
prod-*.
Note
In the preceding example, the deny on
ssm:GetParametersByPath applies only to calls that
request a path matching
prod-*. It doesn't prevent a prod-* parameter
from being returned by a call that requests an ancestor path. To close that
gap, deny ssm:GetParametersByPath on the ancestor paths as
well. For more information, see Restricting access to specific parameters and paths.
The following example shows how to deny some commands while allowing the user
to perform other commands on all parameters that begin with
prod-*.
Note
The parameter history includes all parameter versions, including the
current one. Therefore, if a user is denied permission for
GetParameter, GetParameters, and
GetParametersByPath but is allowed permission for
GetParameterHistory, they can see the current parameter,
including SecureString parameters, using
GetParameterHistory.
The same behavior applies to deletion.
ssm:DeleteParameters is authorized independently of
ssm:DeleteParameter, so denying only
ssm:DeleteParameter doesn't prevent a principal from deleting the
parameter with the DeleteParameters operation. Deny both actions, or
use the pattern ssm:DeleteParameter*.
Encrypting and decrypting parameters using AWS KMS keys
Parameter Store SecureString parameters use AWS KMS keys for encryption. AWS KMS encrypts the value by using either
an AWS managed key or a customer managed key. For more information about AWS KMS and AWS KMS key, see the AWS Key Management Service Developer Guide.
All users within the customer account have access to the default AWS managed key. You can locate the Amazon Resource Name (ARN) of the default key
in the AWS KMS console on the AWS managed keysaws/ssm in the Alias column.
You might want to use the default key to encrypt SecureString parameters while preventing users from working
with SecureString parameters. In this case, the IAM policies must explicitly deny access to the default key, as demonstrated in the following policy example.
When using a customer managed key, the IAM policy that grants a principal access to a
parameter or parameter path must provide explicit kms:Encrypt
permissions for the key. For example, the following policy allows a principal to
create, update, and view SecureString parameters that begin with
prod- in the specified AWS Region and AWS account.
Note
The kms:GenerateDataKey permission is required for creating
encrypted advanced parameters using the specified customer managed key.
If you require fine-grained access control over the SecureString
parameters in your account, use a customer managed key to protect and restrict
access to these parameters. We also recommend using AWS CloudTrail to monitor
SecureString parameter activities.
For more information, see the following topics:
-
Policy evaluation logic in the IAM User Guide
-
Using key policies in AWS KMS in the AWS Key Management Service Developer Guide
-
Viewing events with CloudTrail Event history in the AWS CloudTrail User Guide
Allowing managed nodes to access specific parameters
To control which Parameter Store parameters a managed node can retrieve, you can attach an IAM policy to the instance role. If you
choose the SecureString parameter type when you create your parameter, Systems Manager uses AWS KMS to encrypt the parameter value.
You can view the AWS managed key by running the following command from the AWS CLI.
aws kms describe-key --key-id alias/aws/ssm
The following example allows nodes to get a parameter value only for
parameters that begin with prod-. If the parameter is a
SecureString parameter, then the node decrypts the string using
AWS KMS.
Note
Instance policies, like in the following example, are assigned to the instance role in IAM. For more information about configuring access to Systems Manager features, including how to assign policies to users and instances, see Managing EC2 instances with Systems Manager.
