The AWS official site reads role as a collection of permissions and group as a collection of users. But still they look the same to me. You attach policies to groups or roles, and then assign groups or roles to a user. What exactly are the differences between role and group?
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6 Answers
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AWS Groups are the standard groups which you can consider as collection of several users and a user can belong to multiple groups.
AWS IAM Roles are all together different species; they operate like individual users except that they work mostly towards the impersonation style and perform communication with AWS API calls without specifying the credentials.
Given that IAM Roles are little different, I am emphasizing only that. There are several types of IAM Roles like EC2 IAM Roles, Lambda etc. If you consider, you can launch an EC2 instance with an EC2 IAM Role; hence forth any AWS API related communication wouldn't require any AWS Access Key or Secret key for authentication rather can call the APIs directly (however the long answer is - it uses STS and continuously recycles the credentials behind the scenes); the privileges or permissions of what it can do is determined by the IAM Policies attached to the IAM Role.
Lambda IAM Role works exactly the same, except that only Lambda function can use the Lambda IAM Role etc.
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Users: End User (Think People).
Groups: A collection of users under one set of permissions (permission as policy). As per IAM standards we create groups with permissions and then assign user to that group.
Role: you create roles and assign them to AWS resource (AWS resource example can be a customer, supplier, contractor, employee, an EC2 instance, some external application outside AWS) but remember you can't assign role to user.
It’s not only users who will login, sometimes applications need access to AWS resources. For example, an EC2 instance might need to access one or more S3 buckets. Then, an IAM role needs to be created and attached to the EC2 instance. That role can be re-used by different EC2 instances.
Remember : Groups are for living. Roles are for non-living.
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I was confused all the time about the difference between these two functions.
In short,
Role is like a tag with all the preset policies that can attach on IAM users/groups or AWS services. IAM users share the same account with the account root user (Admin) but with assigned permissions by the root user to use AWS resources within that account.
Therefore, IAM users can directly interact with AWS services; whereas IAM roles cannot make direct requests to AWS services, they are meant to be assumed by authorised entities like an IAM user or an instance. https://aws.amazon.com/iam/faqs/
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I think of an AWS Role as a kind of 'sudo', where each AWS Role can temporarily provide a very specific set of elevated privileges, but without needing the elevated credentials. I get the impression that like sudo, AWS Roles try to prevent privileged actions being used accidentally. I'd be interested to hear if others agree with this analogy.
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Only one IAM Role can be assumed at a time! And there are several situations which fits exactly this kind of permission.
Read the faq about: How many IAM roles can I assume?
The underlaying tool in use is "Permission" in both of the use cases namely: Group and IAM Role.
Group or IAM Role --> Has Policy --> Policy defines permisions --> Permissions are assigned to a Group or IAM Role.
