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partition: The second part describes the partition of AWS you’re using.

arn: The first part is always “arn”, regardless of the resource type.As you move from left to right, each part gets more specific about the particular resource it identifies.Īrn:partition:service:region:account-id:resource An ARN is structured into 6 parts, each separated by a colon. This ARN uniquely identifies a single AWS resource across all AWS accounts. The resource element describes the AWS resources to which the statement applies.Įvery AWS resource is given an Amazon Resource Name, or ARN. The second critical part of an IAM statement is the Resource. Check out the “Be Careful with Wildcards” piece in the Best Practices section below. You should be careful when using wildcards in your Actions to avoid unintentionally granting broad access. s3:Get*: This would affect all S3 actions that start with “Get”, such as “GetObject”, “GetBucketPolicy”, and “GetBucketLocation”.s3:*: This would affect all actions within the S3 service.*: This would affect all API actions across AWS, including all actions in S3 but also all actions in EC2, SQS, DynamoDB, etc.

For example, each of the following is a valid action: You can use the wildcard at the beginning, middle, or end of your action, or as the entire action if you want to write a statement about all actions. When writing actions, you can use an asterisk to act as a wildcard on your action.

s3:ListAllMyBuckets: For listing all of the S3 buckets in your AWS account.

s3:ListBucket: For reading the objects in an S3 bucket.

s3:PutObject: For writing an object to S3.

s3:GetObject: For reading an object on S3.

When writing IAM statements for S3 access, some of the popular actions you will use are: There are 51 different actions within S3 alone. Action is in the form of “:”, where the resource is a particular AWS service (e.g., s3, ec2, or dynamodb) and the verb is a particular action to take within that service (e.g. IAM Statement Elements: ActionĪction describes the API actions that the statement affects. We’ll take a look at each of these separately. There are three critical elements to an IAM statement. The number of characters varies from 2,048 characters to 10,240 characters depending on the type of policy. There is no limit on the number of IAM statements in an IAM policy, though there are limits on the number of characters in an IAM policy. There are two IAM statements in this example - one is from lines 4-8, and the other is from lines 9-13. The value of the “Statement” key is an array of IAM statements.

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An IAM policy is a JSON document with an optional “Version” key plus a “Statement” key. The entire document from lines 1-15 is the IAM policy. Let’s take a look at the example below of an IAM policy being created in the AWS console. At the core of IAM’s authorization system is an IAM policy. IAM is an AWS service for managing both authentication and authorization in determining who can access which resources in your AWS account. However, the same syntax in IAM policies is also used for S3 bucket policies that were discussed in the previous part in this series. Identity-based policies are used mostly within AWS Identity and Access Management (IAM), so we will refer to them as IAM policies throughout this post. Writing identity-based policies within IAM is the main focus of this Part II of our series. Permissions are managed by writing identity-based policies, which are collections of statements. Permissions refer to what a particular identity is allowed to do in the AWS account. We will cover more about best practices for managing IAM identities in Part III of this series.

This topic includes IAM users and groups, credentials, and roles.

Identities refer to the various mechanisms that AWS provides to identify who is requesting a particular AWS action, for authenticating that person or entity, and for organizing similar entities into groups. When thinking about IAM, there are two broad categories to consider: identities and permissions. In Part II, we will take a deeper look at managing access to your S3 resources using AWS Identity and Access Management (IAM). In Part I of this series, we discussed the different mechanisms you can use to allow access to your Amazon S3 buckets and objects.

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This is the second in a three-part series on Amazon S3 Security In-Depth.