iam

AWS IAM

AWS Identity and Access Management (IAM) enables secure access control to AWS services and resources. IAM is foundational to AWS security—every AWS API call is authenticated and authorized through IAM.

Table of Contents

• Core Concepts
• Common Patterns
• CLI Reference
• Best Practices
• Troubleshooting
• References

Core Concepts

Principals

Entities that can make requests to AWS: IAM users, roles, federated users, and applications.

Policies

JSON documents defining permissions. Types:

• Identity-based: Attached to users, groups, or roles
• Resource-based: Attached to resources (S3 buckets, SQS queues)
• Permission boundaries: Maximum permissions an identity can have
• Service control policies (SCPs): Organization-wide limits

Roles

Identities with permissions that can be assumed by trusted entities. No permanent credentials—uses temporary security tokens.

Trust Relationships

Define which principals can assume a role. Configured via the role's trust policy.

Common Patterns

Create a Service Role for Lambda

AWS CLI:

# Create the trust policy
cat > trust-policy.json << 'EOF'
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": { "Service": "lambda.amazonaws.com" },
      "Action": "sts:AssumeRole"
    }
  ]
}
EOF

# Create the role
aws iam create-role \
  --role-name MyLambdaRole \
  --assume-role-policy-document file://trust-policy.json

# Attach a managed policy
aws iam attach-role-policy \
  --role-name MyLambdaRole \
  --policy-arn arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

boto3:

import boto3
import json

iam = boto3.client('iam')

trust_policy = {
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {"Service": "lambda.amazonaws.com"},
            "Action": "sts:AssumeRole"
        }
    ]
}

# Create role
iam.create_role(
    RoleName='MyLambdaRole',
    AssumeRolePolicyDocument=json.dumps(trust_policy)
)

# Attach managed policy
iam.attach_role_policy(
    RoleName='MyLambdaRole',
    PolicyArn='arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole'
)