IAM Policy Enforcement

Enforce IAM policies in LocalStack to test your policies


IAM Policy Enforcement feature can be used to test your security policies and create a more realistic environment that more closely resembles real AWS. The environment configuration ENFORCE_IAM=1 is required while starting LocalStack to enable this feature. Per default, IAM enforcement is disabled, and all APIs can be accessed without authentication.

Getting started

This guide is designed for users new to IAM Policy Enforcement and assumes basic knowledge of the AWS CLI and our awslocal wrapper script.

Start your LocalStack container with the DEBUG=1 and ENFORCE_IAM=1 environment variables set:

$ DEBUG=1 ENFORCE_IAM=1 localstack start

We will demonstrate IAM Policy Enforcement, by creating a user and obtaining the access/secret keys. We will make an attempt to create a bucket using the userโ€™s credentials, which inevitably fails due to insufficient permissions.

Lastly, a policy is attached to the user, granting the necessary s3:CreateBucket permission, thereby enabling the successful creation of the bucket.

Create a user

To follow this guide, open two separate terminal sessions: Terminal 1 for the administrative IAM commands, which will utilize the default root IAM user, and Terminal 2 for executing the commands under the test IAM user you are about to create. This way, we can demonstrate the differentiation in access permissions between the administrative and test users in real-time.

In Terminal 1, execute the following commands to create a test user and obtain the access/secret keys:

$ awslocal iam create-user --user-name test
{ "User": { "Path": "/", "UserName": "test", "UserId": "d7ryukg7bls4rq1ihq1d", "Arn": "arn:aws:iam::000000000000:user/test", "CreateDate": "2023-11-03T12:20:12.332000Z" } }
$ awslocal iam create-access-key --user-name test
{ "AccessKey": { "UserName": "test", "AccessKeyId": "LKIAQAAAAAAAHFR7QTN3", "Status": "Active", "SecretAccessKey": "EYUHpIol7bRJpKd/28c/LI2C4bbEnp82LJCRwXRV", "CreateDate": "2023-11-03T12:20:27Z" } }

Attempt to create a bucket

Navigate to Terminal 2, where we will configure the access keys for the user test in the environment. Once the access keys are set, you will attempt to create an S3 bucket using these credentials.

$ awslocal s3 mb s3://mybucket
make_bucket failed: s3://mybucket An error occurred (AccessDeniedException) when calling the CreateBucket operation: Access to the specified resource is denied

As anticipated, the attempt to create the bucket fails with an AccessDeniedException error, confirming that user test lacks the necessary permissions for this action. You can view the LocalStack logs to validate the policy enforcement:

2023-11-03T12:21:10.971  INFO --- [   asgi_gw_1] l.s.i.p.handler            : Request for service 's3' by principal 'arn:aws:iam::000000000000:user/test' for operation 'CreateBucket' denied.
2023-11-03T12:21:10.972  INFO --- [   asgi_gw_1] localstack.request.aws     : AWS s3.CreateBucket => 403 (AccessDenied)

Attach a policy to the user

Let’s now return to Terminal 1 and execute the following commands to attach a policy to the user test:

$ awslocal iam create-policy --policy-name p1 --policy-document '{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Action":"s3:CreateBucket","Resource":"*"}]}'
$ awslocal iam attach-user-policy --user-name test --policy-arn arn:aws:iam::000000000000:policy/p1

Create a bucket

Now, let’s switch back to Terminal 2 and observe how the bucket creation succeeds with the test IAM user:

$ awslocal s3 mb s3://mybucket
make_bucket: mybucket

The bucket creation succeeds, confirming that the user test now has the necessary permissions to perform this action. You can view the LocalStack logs to validate the policy enforcement:

2023-11-03T12:23:11.469  INFO --- [   asgi_gw_1] localstack.request.aws     : AWS iam.CreatePolicy => 200
2023-11-03T12:23:15.753  INFO --- [   asgi_gw_1] localstack.request.aws     : AWS iam.AttachUserPolicy => 200
2023-11-03T12:23:22.795  INFO --- [   asgi_gw_2] localstack.request.aws     : AWS s3.CreateBucket => 200

You can further use the IAM Policy Enforcement feature to test your Infrastructure as Code (IaC) deployments and ensure that your policies are correctly enforced. If the IAM policies are not correctly enforced, you will get an unsuccessful response from the API call, and the LocalStack logs will provide you with the necessary information to debug the issue.