The correct answer is: Create an IAM role that includes permissions to write to the S3 bucket, and reference this role in the ECS task definition using the taskRoleArn parameter.

This is the most secure and scalable approach. ECS tasks can assume IAM roles that grant least-privilege access to specific AWS services, in this case, S3. By assigning the role via taskRoleArn in the task definition, you ensure the container can make authorized S3 API calls without relying on instance-level roles or static credentials.

Why the other options are incorrect:

Updating an existing S3 IAM role to allow ECS access and relaunching the container may sound plausible, but IAM roles are not associated with S3. Instead, permissions to access S3 are granted to the principal (such as an ECS task), not the resource itself. This option confuses the direction of access control.

Creating a security group to allow ECS access to S3 misunderstands the way AWS networking and permissions work. Amazon S3 is a global service accessed via public endpoints. Access to S3 is governed by IAM policies, not VPC security groups.

Creating an IAM user with S3 permissions and logging into the EC2 instance introduces poor security practices. IAM users are for human access, not automated processes like containers. Using static credentials on EC2 to allow containerized apps to access S3 violates best practices and increases the risk of credential leakage.

Why this question is important: Many candidates confuse IAM roles and users, or incorrectly associate security groups with service-level access. This question tests the ability to implement least-privilege access using IAM and understand ECS task role configuration.

Tip for solving similar questions: Look for keywords like "ECS task" or "Lambda function" and match them to IAM role attachment points such as taskRoleArn or executionRoleArn. Eliminate any options that refer to IAM users or static credentials in automation workflows.

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