Understanding AWS IAM: Users, Groups, Roles, and Policies
Learn the basics of AWS IAM and understand how users, groups, roles, and policies work together to securely control access to AWS resources. This beginner-friendly guide also introduces authentication, authorization, and the principle of least privilege.
As I continued learning AWS, I realized that creating cloud resources is only one part of working with AWS.
Another important question is:
Who is allowed to access those resources, and what are they allowed to do?
This is where AWS Identity and Access Management (IAM) comes in.
IAM helps us securely control access to AWS resources by managing identities, credentials, and permissions.
What is AWS IAM?
AWS Identity and Access Management (IAM) is a service that helps control who can access AWS resources and what actions they can perform.
In simple words:
IAM = Authentication + Authorization + Permissions
For example, suppose we have an S3 bucket.
We may want one person to:
- View objects
- Upload objects
But we may not want that person to:
- Delete the bucket
- Change security settings
IAM allows us to define these permissions.
👤 IAM Users
An IAM user is an identity created in an AWS account.
A user can represent a person who needs access to AWS resources.
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AWS Account
│
├── Developer
├── Tester
└── AdministratorEach user can have permissions based on the policies assigned to them.
AWS recommends avoiding the root user for everyday tasks and using appropriate IAM identities instead.
IAM Groups
An IAM group is a collection of IAM users.
Groups make it easier to manage permissions for multiple users.
For example:
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Developers Group
│
├── Rohit
├── Aman
└── PriyaInstead of attaching the same policies individually to every developer, we can attach policies to the group.
All users in that group receive the permissions assigned to the group.
IAM Roles
An IAM role is an identity that provides permissions through temporary credentials.
Roles are especially useful when an AWS service or application needs to access another AWS service.
For example, suppose an EC2 instance needs to read files from an S3 bucket.
Instead of storing long-term AWS access keys inside the EC2 instance, we can attach an IAM role to the instance.
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EC2 Instance
│
↓
IAM Role
│
↓
S3 Permissions
│
↓
S3 BucketIAM roles are useful for temporary access, federated access, cross-account access, and applications running on EC2.
What is an IAM Policy?
An IAM policy is a document that defines permissions.
Most IAM policies are stored as JSON documents.
A policy can specify:
- Who can perform an action
- What action they can perform
- Which resource they can access
- Under which conditions access is allowed
For example, a simplified policy might allow a user to list an S3 bucket:
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{
"Effect": "Allow",
"Action": "s3:ListBucket",
"Resource": "*"
}Policies can be attached to identities such as users, groups, and roles. Some AWS services also support resource-based policies.
Allow vs Deny
One of the most important IAM concepts is understanding Allow and Deny.
If a request does not have the required permission, it is denied by default.
An explicit Deny overrides an Allow.
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Allow → Access
Deny → No AccessEven if one policy allows an action, an applicable explicit deny can prevent that action.
How Users, Groups, Roles, and Policies Work Together
A simple way to understand the relationship is:
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IAM
│
┌────────┼────────┐
│ │ │
Users Groups Roles
│ │ │
└────────┼────────┘
│
Policies
│
↓
AWS ResourcesFor example:
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Developers Group
│
↓
IAM Policy
│
↓
EC2 + S3 PermissionsThis makes permission management much easier.
Authentication vs Authorization
These two terms can initially be confusing.
Authentication
Authentication answers:
Who are you?
For example, signing in with valid credentials.
Authorization
Authorization answers:
What are you allowed to do?
For example:
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User → Can read S3
User → Cannot delete S3 bucketPrinciple of Least Privilege
One of the most important security concepts I learned is the principle of least privilege.
It means giving a user, application, or service only the permissions it actually needs.
For example, if an application only needs to read objects from S3, there is no reason to give it full S3 administrator permissions.
Instead:
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Bad:
Application → Full AWS Access
Better:
Application → Read-only S3 AccessThis reduces the potential impact if credentials or an application are compromised.
Simple Real-World Example
Imagine we are building a web application.
We have:
- Developers
- EC2 servers
- An S3 bucket
- A database
We could organize access like this:
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AWS Account
│
┌─────────┴─────────┐
│ │
Developers EC2 Application
│ │
↓ ↓
IAM Group IAM Role
│ │
↓ ↓
Policies S3 Permissions
│
↓
S3 BucketDevelopers can receive only the permissions they need, while the EC2 application can use a role to access AWS resources without embedding long-term credentials in the application.
What I Learned
Before learning IAM, I mainly focused on creating and configuring AWS services.
Now I understand that security and access control are equally important.
The main concepts I learned are:
- IAM → Manages access to AWS resources
- User → Represents an identity
- Group → Organizes users and permissions
- Role → Provides permissions through temporary credentials
- Policy → Defines what actions are allowed or denied
- Least Privilege → Give only the permissions that are actually required
Understanding IAM is an important step toward building secure AWS applications.
I'm continuing my AWS learning journey and exploring more cloud and security concepts step by step.
#AWS #IAM #CloudComputing #AWSBeginner #CloudSecurity
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