AWS IAM Server Access: A Guide

TL;DR

Yes, AWS Identity and Access Management (IAM) is the way to manage access to your servers running on Amazon Web Services. It lets you control who can do what with your resources, improving cyber security and making administration easier.

How to Use IAM for Server Access

1. Understand Roles vs. Users:

• IAM Users: Represent individual people or applications needing access. Generally avoid directly assigning permissions to users; use roles instead.
• IAM Roles: Assume identities, granting temporary credentials. This is the preferred method for servers (like EC2 instances) because it avoids storing long-term credentials on your machines.

Create an IAM Role for Your Servers:

• Go to the IAM console in AWS.
• Click ‘Roles’ then ‘Create role’.
• Select ‘AWS service’ as the trusted entity, and choose the service your server uses (e.g., EC2).
• Attach policies that define what permissions the role has. Start with least privilege – only grant access to what’s absolutely necessary. Examples include:
  • AmazonEC2ReadOnlyAccess: Allows viewing EC2 instance details but not modification.
  • S3FullAccess: (Use cautiously!) Grants full control over S3 buckets. Prefer more specific policies if possible.
  • IAMReadOnlyAccess: Allows viewing IAM resources, useful for auditing.

Attach the Role to Your Servers:

• EC2 Instances: When launching an EC2 instance, you can specify an IAM role in the ‘Configure Instance Details’ step. Alternatively, you can attach a role to a running instance via the AWS console or CLI.
• Other Services: The process varies depending on the service. Consult the AWS documentation for your specific server type (e.g., Lambda functions, ECS tasks).

Verify Access:

• Connect to your server via SSH or other means.
• Use the AWS CLI to test if the role has the expected permissions. For example:

  aws s3 ls

  If you attached a policy allowing S3 access, this command should list your buckets. If not, you’ll get an ‘Access Denied’ error.

Using the AWS CLI with IAM Roles (for servers):

• The AWS CLI automatically retrieves temporary credentials from the instance metadata service when running within a server that has an associated IAM role. You don’t need to configure access keys manually.
• Ensure your server’s operating system has the latest version of the AWS CLI installed and configured (though minimal configuration is needed).

Security Best Practices:

• Least Privilege: Grant only the permissions necessary for each role.
• Regular Audits: Review IAM policies regularly to ensure they are still appropriate and haven’t become overly permissive.
• Multi-Factor Authentication (MFA): Enable MFA for all IAM users.
• Role Session Duration: Configure role session duration appropriately. Shorter durations reduce the risk of compromised credentials being used for extended periods.