Grant AWS Lambda Access to Secrets Manager

Grant AWS Lambda Access to Secrets Manager #

In order to grant a Lambda function access to Secrets Manager, we have to attach an IAM policy to the function's execution role. The policy should grant permissions for all the Actions the function needs to perform on the secrets.

For example, the following policy grants permissions for the most commonly used secrets manager actions on a specific secret.

The policy applies to a specific secret, therefore make sure to replace the YOUR_SECRET_ARN placeholder in the Resource element with the secret's ARN.
You can specify multiple values if the lambda function needs access to multiple secrets.

example-secrets-manager-policy.json

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{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
              "secretsmanager:GetSecretValue",
              "secretsmanager:DescribeSecret",
              "secretsmanager:ListSecretVersionIds",
              "secretsmanager:PutSecretValue",
              "secretsmanager:UpdateSecret",
              "secretsmanager:TagResource",
              "secretsmanager:UntagResource"
            ],
            "Resource": [
              "YOUR_SECRET_ARN"
            ]
        }
    ]
}

If your lambda function only needs to read a secret, you only need the secretsmanager:GetSecretValue action.

The actions your lambda function needs to perform on the secrets are use case specific.

You could set "secretsmanager:*" for the Action element in the policy to grant full secrets manager access to the lambda function. However, it's best practice to grant an entity the least permissions that get the job done.

You can view a full list of the secrets manager Actions in the Secrets Manager Actions table.

There is a Description column that explains what each action does.

To attach a policy to the lambda function's execution role, you have to:

Open the AWS Lambda console and click on your function's name
Click on the Configuration tab and then click Permissions

click on function role

Click on the function's role
Click on Add permissions and then click Create inline policy

create inline policy

In the JSON editor, paste the following policy.

Replace the YOUR_SECRET_ARN placeholder and adjust the Actions your lambda function needs to execute.

example-secrets-manager-policy.json

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{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
              "secretsmanager:GetSecretValue",
              "secretsmanager:DescribeSecret",
              "secretsmanager:ListSecretVersionIds",
              "secretsmanager:PutSecretValue",
              "secretsmanager:UpdateSecret",
              "secretsmanager:TagResource",
              "secretsmanager:UntagResource"
            ],
            "Resource": [
              "YOUR_SECRET_ARN"
            ]
        }
    ]
}

Click Review Policy and give your policy a name, then click Create policy

At this point the lambda function's role has been extended with a policy that grants access to some secrets manager actions on a specific secret.

It can take up to a minute until the IAM changes have been propagated and the policy is in effect.

Invoke your lambda function and verify whether it has access to the secret.

If your function is still unable to access the Secrets manager secret, try to increase the function's timeout by a second in the AWS console, or simply add an extra print statement in the code and click the Deploy button.

If your lambda function still doesn't have access to the secret, expand the IAM policy you added to the function's role and edit it to look like the policy below.

edit policy

Replace the YOUR_SECRET_ARN placeholder with secret's ARN.

secrets-manager-full-access.json

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{
    "Version": "2012-10-17",
    "Statement": [
        {
          "Effect": "Allow",
          "Action": [
              "secretsmanager:*"
            ],
          "Resource": [
            "YOUR_SECRET_ARN"
          ]
        }
    ]
}

The IAM policy above grants full access to a specific secret. Your lambda function will be able to execute all Secrets Manager actions on the secret.

It's a best practice to grant the least possible permissions that enable you to get the job done, however the * symbol is useful when debugging.

After you've updated the policy, try to invoke your lambda function again, it should have permissions to execute any action on the secret.

After you verify which actions your lambda needs to run, you can make the IAM policy less permissive.

Note that a policy statement with a Deny effect will always override any Allow statements.

Grant AWS Lambda Access to Secrets Manager

Grant AWS Lambda Access to Secrets Manager #

Further Reading #

Borislav Hadzhiev