IAM User vs Role in AWS: Key Differences and When to Use Each

An IAM user is a permanent identity with long-term credentials for a person or service, while an IAM role is a temporary identity assumed by trusted entities to gain specific permissions. Users have fixed credentials, but roles provide temporary, limited access without permanent credentials.

Quick Comparison

This table summarizes the main differences between IAM users and IAM roles in AWS.

Factor	IAM User	IAM Role
Identity Type	Permanent identity with credentials	Temporary identity assumed by trusted entities
Credentials	Long-term (password, access keys)	Temporary security tokens
Use Case	Individual people or services needing direct access	Delegation, cross-account access, AWS services
Permissions	Attached directly to user or groups	Attached to the role and assumed dynamically
Security	Risk if credentials are leaked	More secure due to temporary credentials
Access Duration	Persistent until revoked	Limited by session duration

Key Differences

IAM users represent permanent identities in AWS. They have long-term credentials like passwords and access keys that allow direct login or API access. Users are best for individuals or services that need consistent, ongoing access to AWS resources.

IAM roles do not have permanent credentials. Instead, trusted entities such as users, AWS services, or applications temporarily assume roles to gain permissions. Roles provide temporary security tokens that expire, reducing risk if compromised.

Roles are ideal for delegation, cross-account access, or granting AWS services permissions without embedding credentials. Users have fixed permissions, while roles allow flexible, temporary access based on the situation.

Code Comparison

Here is an example of creating an IAM user with permissions to list S3 buckets using AWS CLI.

bash

aws iam create-user --user-name ExampleUser
aws iam attach-user-policy --user-name ExampleUser --policy-arn arn:aws:iam::aws:policy/AmazonS3ReadOnlyAccess

Output

User created and AmazonS3ReadOnlyAccess policy attached to ExampleUser

IAM Role Equivalent

Here is how to create an IAM role with the same S3 read-only permissions and trust policy for EC2 to assume it.

bash

aws iam create-role --role-name ExampleRole --assume-role-policy-document '{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Principal":{"Service":"ec2.amazonaws.com"},"Action":"sts:AssumeRole"}]}'
aws iam attach-role-policy --role-name ExampleRole --policy-arn arn:aws:iam::aws:policy/AmazonS3ReadOnlyAccess

Output

Role created with trust policy for EC2 and AmazonS3ReadOnlyAccess policy attached

When to Use Which

Choose IAM user when you need a permanent identity with long-term credentials for a person or service that requires direct AWS access. This is common for developers or administrators.

Choose IAM role when you want to grant temporary, limited access without sharing permanent credentials. Roles are best for cross-account access, AWS services like EC2, or applications that assume permissions dynamically for better security.

Key Takeaways

IAM users have permanent credentials and represent fixed identities.

IAM roles provide temporary credentials and are assumed by trusted entities.

Use users for direct, ongoing access by individuals or services.

Use roles for temporary, delegated access and better security.

Roles are essential for cross-account and AWS service permissions.