IAM – Deciding Which one to use

AWS IAM Users, Groups, and Roles Explained in Layman Terms

What Are They?

1. IAM Users:

   • Who are they?: Imagine IAM users as individual people who need access to your AWS resources. Each user gets their own username and password.
   • Example: Think of a user as your friend Bob who needs to log into your AWS account to help manage your cloud servers.

2. IAM Groups:

   • Who are they?: Groups are collections of users. They help manage permissions for multiple users at once by assigning policies to the group instead of each user individually.
   • Example: Imagine you have a team of developers. Instead of setting permissions for each developer one by one, you create a group called “Developers” and assign permissions to the group.

3. IAM Roles:

   • Who are they?: Roles are a bit different. They are permissions you can assign to entities (like users or applications) that don’t belong to your account or to AWS services. Roles are temporary and can be assumed by anyone who needs them, provided they have the right permissions.
   • Example: Think of a role as a visitor badge in an office. You give it to a contractor so they can access the building temporarily while they work on a project.

How to Decide Which One to Use?

1. IAM Users:

   • Use when: You have individuals (like employees) who need long-term access to AWS resources. Each person needs their own secure login.
   • Example: Use IAM users for team members who regularly log into AWS to manage resources.

2. IAM Groups:

   • Use when: You need to manage permissions for multiple users with similar job functions. Groups help streamline permission management.
   • Example: Use IAM groups to manage permissions for a department like developers, testers, or accountants.

3. IAM Roles:

   • Use when: You have applications, services, or users from other accounts that need temporary access to your AWS resources. Roles can be assumed when needed.
   • Example: Use IAM roles for a web application running on an EC2 instance that needs to access S3 buckets or for a third-party contractor working on a specific project.

How Can They Be Combined?

1. Users and Groups:

   • Combine users into groups to simplify permission management. Instead of assigning permissions to each user, assign them to a group.
   • Example: Add all your developers to a “Developers” group and assign the necessary permissions to the group. Any user in the group inherits those permissions.

2. Users and Roles:

   • Users can assume roles to gain temporary access to additional permissions that they do not usually have.
   • Example: Bob is a developer with specific permissions, but occasionally, he needs to perform admin tasks. Bob can assume an admin role temporarily to gain those permissions.

3. Roles and Services:

   • AWS services like EC2 can assume roles to perform actions on your behalf without embedding credentials.
   • Example: An EC2 instance needs to read data from an S3 bucket. Assign a role to the EC2 instance with the necessary permissions to access the bucket.

Strengths, Weaknesses, and Limitations

1. IAM Users:

   • Strengths:
     • Fine-grained control over individual permissions.
     • Each user has a unique identity.
   • Weaknesses:
     • Can become complex to manage if there are many users.
   • Limitations:
     • Each user requires separate credential management.

2. IAM Groups:

   • Strengths:
     • Simplifies permission management for multiple users.
     • Easy to add/remove users from groups.
   • Weaknesses:
     • Permissions apply to all users in the group, which might not be suitable for users with slightly different needs.
   • Limitations:
     • Groups cannot be nested (one group cannot contain another group).

3. IAM Roles:

   • Strengths:
     • Provides temporary, flexible permissions.
     • Ideal for cross-account access and service access.
   • Weaknesses:
     • Can be complex to set up correctly.
   • Limitations:
     • Roles are not ideal for users needing long-term, stable access.

Summary

• IAM Users are individual accounts for people who need long-term access.
• IAM Groups help manage permissions for multiple users easily.
• IAM Roles are temporary permission sets that can be assumed by users or services when needed.

Using a combination of users, groups, and roles can help efficiently manage access and permissions in AWS, ensuring security and ease of use. For example, regular employees might use IAM users and groups for their daily tasks, while roles are used for special projects or cross-account access.