How do you allow an external role to access your AWS resource directly?

Question

Hi,

Here's the setup:

We both manage two AWS accounts (Account1 and Account2). In the Account1, we have an application that will assume a role to access a DynamoDB table in the Account2. How do we grant permission to the (external) role directly to the DynamoDB table? We understand that role-chaining is the suggested approach, but it is not a possibility for us right now for some reason.

Answer

Hello,

Below are the links to the official documentation that address your issue, please have a look -

https://docs.aws.amazon.com/glue/latest/dg/aws-glue-programming-etl-dynamo-db-cross-account.html
https://docs.aws.amazon.com/prescriptive-guidance/latest/patterns/configure-cross-account-access-to-amazon-dynamodb.html

Thanks

Answer

To allow an application in AWS Account1 to access a DynamoDB table in Account2 without role-chaining, follow these steps:

1. **Create an IAM Role in Account1**: This role is for your application, with a trust relationship allowing it to assume the role.

#### Trusted Policy (example):
```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::Account1-ID:role/Role1"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}
```
#### permission policy (example):
```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "sts:AssumeRole",
      "Resource": "arn:aws:iam::Account2-ID:role/Role2"
    }
  ]
}
```
2. **Grant Access in Account2**:
   - Modify the IAM policy attached to the DynamoDB table in Account2.
   - Include a statement in the policy that allows the IAM role from Account1 access to the table. Use the role's ARN in the `Principal` field and specify the actions (e.g., `dynamodb:GetItem`, `PutItem`) your application needs.

#### Trusted policy (example):
```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::Account1-ID:role/Role1"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}
```

#### Permission policy (example):
```json
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::Account2-ID:role/Role2"
            },
            "Action": [
                "dynamodb:GetItem",
                "dynamodb:Query",
                "dynamodb:Scan",
                "dynamodb:PutItem",
                "dynamodb:UpdateItem",
                "dynamodb:DeleteItem"
            ],
            "Resource": "arn:aws:dynamodb:Region:Account2-ID:table/YourTableName"
        }
    ]
}
```

How do you allow an external role to access your AWS resource directly?

Trusted Policy (example):

permission policy (example):

Trusted policy (example):

Permission policy (example):

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