AWS Trust Policy Example: Securing Your AWS Resources

Table of contents
  1. Understanding Trust Policies in AWS
  2. Example of an AWS Trust Policy
  3. Best Practices for Creating Trust Policies
  4. Conclusion

When it comes to securing your AWS (Amazon Web Services) resources, trust policies play a crucial role. By specifying the entities that are allowed to assume roles and the conditions under which they can do so, trust policies help you control access to your AWS environment. In this comprehensive guide, we'll explore AWS trust policies and provide real-world examples to help you understand how to effectively use them to secure your AWS resources.

Understanding Trust Policies in AWS

Before we dive into trust policy examples, it's important to have a clear understanding of what trust policies are and how they work in AWS. In AWS, trust policies are JSON documents that define which accounts or services are trusted to assume a particular role. These policies are attached to IAM (Identity and Access Management) roles and are essential for establishing trust relationships between different AWS accounts and services.

When a principal entity, such as an IAM user, requests access to a resource in AWS, the trust policy attached to the role associated with the resource is evaluated to determine whether the request should be allowed. Trust policies specify the conditions under which the trusted entity is permitted to assume the role, adding an extra layer of security to your AWS environment.

Components of a Trust Policy

AWS trust policies consist of several components, including:

  • Effect: This specifies whether the trust relationship is "Allow" or "Deny."
  • Principal: The entity that is allowed to assume the role. This can be an AWS account, IAM user, IAM role, AWS service, or another principal.
  • Action: The actions that the trusted entity is allowed to perform when assuming the role.
  • Condition: Additional conditions that must be met for the trust policy to be in effect, such as time-based restrictions or IP address conditions.

Example of an AWS Trust Policy

Let's dive into a real-world example of an AWS trust policy to illustrate how it's structured and what it accomplishes. Consider the following trust policy, which allows an AWS Lambda function in one account to assume a role in another account:

  "Version": "2012-10-17",
  "Statement": [
      "Effect": "Allow",
      "Principal": {
        "Service": ""
      "Action": "sts:AssumeRole",
      "Condition": {
        "StringEquals": {
          "aws:SourceAccount": "123456789012"

In this example, the trust policy allows the AWS Lambda service to assume a role in the specified AWS account (with the account ID "123456789012"). The conditions set in the trust policy ensure that the Lambda function from the specified account is allowed to assume the role, adding a layer of control and security to the trust relationship.

Key Takeaways from the Example

From the example above, we can extract several key takeaways:

  1. The "Effect" is set to "Allow," indicating that the trust relationship is permitted.
  2. The "Principal" is specified as the Lambda service using the "Service" keyword.
  3. The "Action" is set to "sts:AssumeRole," defining the action that the Lambda service is allowed to perform.
  4. The "Condition" restricts the trust relationship to a specific source account using the "aws:SourceAccount" condition key.

Understanding and crafting trust policies in this manner is essential for effectively managing access to your AWS resources and ensuring the overall security of your cloud environment.

Best Practices for Creating Trust Policies

When creating trust policies for your AWS resources, it's important to follow best practices to maximize security and maintain a well-organized IAM environment. Here are some best practices to consider:

  • Least Privilege: Ensure that trust policies grant only the permissions needed for the trusted entity to perform its intended actions. Avoid granting overly broad permissions.
  • Regular Review: Periodically review and audit trust policies to ensure that they align with your organization's security requirements and access control policies.
  • Use Conditions Wisely: Leverage conditions in trust policies to add an extra layer of control, such as restricting access based on time, IP address, or other contextual factors.
  • Testing and Validation: Test trust policies in a controlled environment to verify that they work as intended before deploying them in a production environment.


What is the purpose of a trust policy in AWS?

Trust policies in AWS establish trust relationships between different entities, such as AWS accounts or services, and determine which entities are allowed to assume specific roles. These policies play a critical role in controlling access to AWS resources and enhancing security.

Can I have multiple trust policies for a single IAM role?

Yes, you can attach multiple trust policies to a single IAM role, allowing you to establish trust relationships with multiple entities. Each trust policy defines a specific principal entity that is allowed to assume the role, along with the associated conditions.

How often should I review and update trust policies?

It's recommended to review and update trust policies on a regular basis, especially when there are organizational changes, updates to access requirements, or modifications to the AWS environment. Regular reviews help ensure that trust policies align with your security policies and access control needs.


In conclusion, trust policies are a fundamental aspect of securing your AWS resources and managing access to your cloud environment. By understanding the structure of trust policies and following best practices for their creation, you can effectively control access and enhance the overall security posture of your AWS environment. Leveraging real-world examples and best practices, you can confidently craft trust policies that align with your organization's security requirements and access control policies.

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