![]() Select the drop down next to Condition key to list the global condition keys, then the service level condition keys are listed after. The Add request condition dialogue will open. The final step is to expand the request conditions, and choose Add condition. If you’re not familiar with creating policies, you can follow the full instructions in the IAM documentation. You can access the visual editor when you choose Create policy under policies in the IAM console, or add policies when viewing a role, group, or user as shown in Figure 1. The policy I’m going to walk you through creating is to grant an AWS Lambda function permission to get specific objects from Amazon S3, and put items in a specific table in Amazon DynamoDB. If there is a complex policy with many services, I often look at the AWS managed policies as a starting place for the actions that are required, then use the visual editor to fine tune and check the resources and conditions. The visual editor is my default starting place for building policies as I like the wizard and seeing all available services, actions, and conditions without looking at the documentation. For example, a key of aws:CurrentTime can be used to allow access based on date and time. ![]() A global condition key can be used with any service. Condition keys can be service-specific or global. Condition: Allows you to build expressions to match the condition keys and values in the policy against keys and values in the request context sent by the IAM principal.NotResource: Can be used instead of the Resource element to explicitly match every AWS resource except those specified.Resource: Specifies the resources-for example, an S3 bucket or objects-that the policy applies to in Amazon Resource Name ( ARN) format.This element will allow an IAM principal to invoke all API actions to a specific AWS service except those actions specified in this list. NotAction: Can be used as an alternative to using Action.For example, s3:CreateBucket is an Amazon S3 service API action and IAM action that enables an IAM Principal to create an S3 bucket. Action: Describes a specific action or actions that will either be allowed or denied to run based on the Effect entered.Effect: Specifies whether the statement will Allow or Deny an action.The main elements of a policy statement are: ![]() AWS managed policies are provided as examples, cannot be modified, but can be copied, enhanced, and saved as Customer managed policies. Customer managed policies are created and managed by you, the customer. ![]() You can create and attach multiple identity-based policies to your IAM principals, and you can reuse them across your AWS accounts. In this blog, I only give examples for identity-based policies that attach to IAM principals to grant permissions to an identity. In AWS, there are different types of policies that are used for different reasons. These identities start with no permissions and you add permissions using a policy. In AWS, an IAM principal can be a user, role, or group. This blog post will focus on demonstrating how you can use IAM policies to grant restrictive permissions to IAM principals to meet least privilege standards. There are a number of ways to grant access to different types of resources, as some resources support both resource-based policies and IAM policies. For example, if you have an Amazon Elastic Compute Cloud (Amazon EC2) instance that needs to access an Amazon Simple Storage Service (Amazon S3) bucket to get configuration data, you should only allow read access to the specific S3 bucket that contains the relevant data. Least privilege is also one of many Amazon Web Services (AWS) Well-Architected best practices that can help you build securely in the cloud. Least privilege is a principle of granting only the permissions required to complete a task. If you’re not familiar with IAM policy structure, I highly recommend you read understanding how IAM works and policies and permissions. In this post, I’m going to share two techniques I’ve used to write least privilege AWS Identity and Access Management (IAM) policies. December 4, 2020: We’ve updated this post to use s3:CreateBucket to simplify the intro example, replaced figure 8 removing the IfExists reference, and clarified qualifier information in the example.
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