Tutorial / Cram Notes
Instance roles are attached to EC2 instances, allowing software running on those instances to interact with AWS resources. The instance role is associated with an IAM role, which avoids the need to store AWS credentials on the instance. Instead, the role provides temporary credentials that are automatically rotated and provided to the instance.
The permissions assigned to an instance role determine what actions the EC2 instance can perform. For example, you might have an application server that needs to access an S3 bucket. By creating an IAM role with the necessary permissions and associating it with your EC2 instance, the application can make calls to S3 securely.
How to assign an instance role to an EC2 instance:
- Create an IAM role and define the permission policy.
- Launch an EC2 instance and attach the IAM role to it.
- Use the AWS SDK or CLI from within the instance to interact with AWS services. The instance’s role will enforce the permissions.
Service Roles
In contrast, service roles are used by AWS services themselves and define the actions that services can perform on your behalf. When you enable a service to perform actions in your AWS environment, that service assumes the service role you’ve created for it.
For instance, AWS Lambda may need to read from an S3 bucket and write logs to CloudWatch. In this case, you create a service role with the necessary permissions and configure your Lambda function to assume this role. The Lambda function then executes with the permissions granted by the role.
How to create a service role:
- Create an IAM role and specify the trust relationship that allows the service to assume the role.
- Define the permission policy detailing what this service can and cannot do.
- Configure the AWS service to use this role when performing operations.
Comparing Instance Roles and Service Roles
Here’s a basic comparison table illustrating the primary differences between instance roles and service roles:
| Aspect | Instance Roles | Service Roles |
|---|---|---|
| Purpose | Grant permissions to EC2 instances | Grant permissions to AWS Services |
| Used by | Software running on EC2 Instances | AWS-hosted services (e.g., Lambda) |
| Credentials Management | Temporary credentials automatically rotated | Temporary credentials provided by the service |
| Common Use Cases | Access S3 buckets, DynamoDB tables, etc. | Execute Lambda functions, Run ECS tasks, etc. |
Practical Scenario
Consider the scenario where you have an EC2 instance that needs to process data and then store the results in an RDS database. You require the instance to have readonly access to the S3 bucket my-input-bucket, and full access to the RDS instance my-database.
You would create an IAM role for the EC2 instance with two policies attached:
- An S3 readonly policy for
my-input-bucket. - An RDS full access policy for
my-database.
Once this role is created, you can attach it to your EC2 instance. This will authorize the application on your instance to read from the S3 bucket and interact with the RDS database as per the permissions specified.
Remember, IAM roles and policies are the backbone of AWS security, and mastering their use is a key outcome of preparing for the AWS Certified Security – Specialty exam. Always apply the principle of least privilege, granting only the permissions necessary to perform a task. This helps in reducing the risk and potential impact of security breaches.
Practice Test with Explanation
True/False: Instance roles provide AWS service roles with permissions that allow AWS services to access AWS resources.
- Answer: False
Explanation: Instance roles are IAM roles that provide permissions to the EC2 instances themselves, not to AWS services. Service roles provide AWS services with the necessary permissions to access AWS resources.
True/False: You can attach an IAM user directly to an EC2 instance to grant it permissions.
- Answer: False
Explanation: IAM users cannot be directly attached to EC2 instances. Instead, an instance role should be attached to the EC2 instance to grant necessary permissions to the applications running on the instance.
Which of the following is a best practice when using IAM roles with EC2 instances?
- A) Use a single, broad-access role for all EC2 instances to simplify management.
- B) Create individual IAM users for each EC2 instance.
- C) Assign an IAM role to the EC2 instance with the necessary permissions.
- D) Store static IAM access keys on the instance for applications to use.
Answer: C)
Explanation: Assigning an IAM role with the necessary permissions to an EC2 instance is the recommended best practice as it avoids the use of static access keys and can be easily managed and audited.
True/False: Service roles must be assumed by a user or an application before being used.
- Answer: True
Explanation: Service roles are designed to be assumed by AWS services or by delegated entities within the service, rather than being directly managed or used by end-users.
Which feature allows you to securely deliver credentials to EC2 instances?
- A) EC2 Key Pairs
- B) IAM Users
- C) IAM Roles
- D) AWS KMS
Answer: C)
Explanation: IAM Roles can be used to securely deliver credentials to EC2 instances. These credentials are dynamically delivered and are automatically rotated.
True/False: You can attach multiple IAM roles to a single EC2 instance at the same time.
- Answer: False
Explanation: You can attach only one IAM role to an EC2 instance at a time. However, you can create a role that encompasses all the required permissions.
Service roles for Amazon EC2 Auto Scaling groups are used for what purpose?
- A) To encrypt data on the EC2 instances.
- B) To allow the instances to log data to Amazon CloudWatch.
- C) To give the Auto Scaling group permissions to launch instances.
- D) To enable enhanced networking on EC2 instances.
Answer: C)
Explanation: The service role for Amazon EC2 Auto Scaling groups is used to give the Auto Scaling service permissions to launch and manage EC2 instances on your behalf.
True/False: When an EC2 instance with an attached role is copied to another region, the role is automatically attached to the copy.
- Answer: False
Explanation: When copying an EC2 instance to another region, any IAM roles attached to the original instance are not automatically replicated. The role must be manually attached to the instance in the new region.
Which of the following policies would allow an EC2 instance to access objects in an S3 bucket?
- A) A bucket policy attached to the S3 bucket.
- B) An IAM role with an attached policy providing S3 access, which is then associated with the EC2 instance.
- C) A user policy attached to an IAM user, with the user’s access keys stored on the EC2 instance.
- D) All of the above.
Answer: D)
Explanation: All of these methods would allow an EC2 instance to access objects in an S3 bucket: via a bucket policy, an IAM role, or user policy with access keys stored on the instance. However, option B represents the best practice of using IAM roles for EC2 instances.
True/False: You can attach a service-linked role to a non-AWS application service.
- Answer: False
Explanation: Service-linked roles are a specific type of IAM role that links directly to certain AWS services. They cannot be used with non-AWS application services.
True/False: EC2 instance metadata includes the IAM role’s security credentials.
- Answer: True
Explanation: The EC2 instance metadata provides temporary security credentials associated with the IAM role attached to the EC2 instance, which can be retrieved and used by applications running on the instance.
Which of the following would be a reason to use IAM service roles?
- A) To log in to the AWS Management Console.
- B) To perform actions on behalf of a user.
- C) To enable an AWS service to perform actions on your behalf.
- D) To encrypt data stored on an EBS volume.
Answer: C)
Explanation: IAM service roles are used to grant permissions to AWS services so they can perform actions on your behalf, such as accessing resources they need to function.
Interview Questions
What is the difference between an AWS IAM user and an IAM role in the context of authorizing compute workloads?
An IAM user represents an individual or service which requires access and is primarily used for long-term AWS access credentials. An IAM role, on the other hand, does not have any credentials and is meant to be assumed by authorized entities such as AWS services, users, or applications. For compute workloads, roles provide a more secure and flexible way to grant permissions as they allow for temporary access and avoid the distribution of long-term credentials.
How do you assign an IAM role to an EC2 instance, and when should this be done?
An IAM role is assigned to an EC2 instance through instance profiles. This process can be done either at the launch of the EC2 instance or attached afterward. It is recommended to assign the IAM role at the instance launch to immediately provide the necessary permissions the applications require upon startup.
Can you explain the concept of least privilege and how it applies when authorizing compute workloads with instance roles?
The principle of least privilege entails granting only the permissions needed to perform a specified task, no more, no less. When authorizing compute workloads with instance roles, you should ensure that the roles have only the permissions that are necessary for the tasks the workload needs to accomplish, reducing the risk of unauthorized access or actions.
What is the role of AWS STS (Security Token Service) in relation to instance roles?
AWS STS plays a critical role in the temporary security credentials that are used when an instance role is assumed by an EC2 instance. STS provides these temporary credentials that are automatically rotated and managed, which the EC2 instances use to make secure AWS requests.
How can you restrict an EC2 instance role from being assumed by all EC2 instances?
To restrict an EC2 instance role from being assumed by all EC2 instances, you would use a condition element in the role’s trust policy that specifies a particular instance or a condition that must be fulfilled. For example, you might include a condition that limits access based on the instance’s Amazon Resource Name (ARN) or tags.
What is a service-linked role, and how does it differ from a traditional service role in AWS?
A service-linked role is a unique type of IAM role that is linked directly to an AWS service. It is predefined by the service and includes all the permissions that the service requires to call other AWS services on your behalf. This differs from a traditional service role, which a user manually creates and manages to delegate permissions to AWS services.
In what scenario would you opt for a service role instead of an instance role?
A service role is used when an AWS service needs to perform actions on your behalf across different services, such as when AWS Lambda needs to access S3 or DynamoDB. An instance role, by contrast, is specifically used for assigning permissions to an EC2 instance. You would opt for a service role when the actions are not tied directly to a single EC2 instance’s lifecycle or need to be accomplished by a managed service.
What are the security implications of over-privileged instance roles or service roles?
Over-privileged roles pose a significant security risk because if they are compromised, an attacker could potentially gain wide-ranging access to resources and data, potentially leading to data breaches, infrastructure manipulation, or denial of service. Following the principle of least privilege is essential to mitigate such risks.
How can you monitor the use of IAM roles assigned to EC2 instances to ensure they are being used securely and appropriately?
You can monitor the use of IAM roles assigned to EC2 instances with AWS CloudTrail and AWS Config. CloudTrail logs all API calls, including those made with IAM role credentials, while AWS Config can help to continuously monitor and record your AWS resource configurations, allowing you to audit and assess IAM roles compliance with your desired configurations.
Describe how you would implement role chaining to authorize compute workloads in a multi-account AWS environment.
Role chaining involves assuming an IAM role from an existing IAM role across different AWS accounts, often in a multi-account setup. To implement this, you define a trusted relationship between the roles in different accounts, ensuring the permissions propagate correctly. This allows for structured and secure cross-account access, where a workload can assume a role in one account that, in turn, assumes another role in a different account.
Great article on applying instance roles and service roles for authorizing compute workloads!
Thanks for sharing this! Found it really helpful.
Can someone explain the difference between instance roles and service roles in the context of AWS?
I’m prepping for the AWS Security Specialty exam, and this topic is a bit confusing. Any tips?
Awesome guide! It made instance roles and service roles easy to understand.
How do instance roles differentiate from regular IAM roles?
Very helpful, thank you!
Does applying these roles impact the performance of the compute workloads?