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Amazon Cognito AliasExistsException

The alias (e.g., email or phone number) already exists in the user pool.

Understanding Amazon Cognito

Amazon Cognito is a service provided by AWS that enables developers to add user sign-up, sign-in, and access control to their web and mobile applications quickly and easily. It supports authentication through social identity providers such as Facebook, Google, and Amazon, as well as enterprise identity providers via SAML 2.0 and OpenID Connect.

Recognizing the Symptom: AliasExistsException

When working with Amazon Cognito, you might encounter the AliasExistsException error. This error typically occurs when you attempt to sign up or update a user with an alias (such as an email or phone number) that already exists in the user pool.

What You Observe

When this error occurs, you will see a message indicating that the alias you are trying to use is already associated with another user in the user pool. This prevents the creation of a new user or the update of an existing user's alias.

Explaining the Issue: AliasExistsException

The AliasExistsException is thrown because Amazon Cognito enforces uniqueness for certain attributes, known as aliases. These aliases can include email addresses, phone numbers, or preferred usernames. If an alias is already in use, Cognito will not allow another user to be created or updated with the same alias.

Why This Happens

This error ensures that each alias is unique within the user pool, preventing conflicts and ensuring that users can be uniquely identified by their aliases.

Steps to Resolve AliasExistsException

To resolve this issue, you need to ensure that the alias you are trying to use is unique within the user pool. Here are the steps you can take:

1. Check Existing Users

First, verify if the alias is already associated with an existing user. You can do this by listing users in the user pool and checking their attributes. Use the following AWS CLI command to list users:

aws cognito-idp list-users --user-pool-id --filter "email = \"[email protected]\""

Replace <your_user_pool_id> with your actual user pool ID and [email protected] with the alias you are checking.

2. Update Existing User

If the alias is already in use and you want to update the existing user's alias, you can use the following command:

aws cognito-idp admin-update-user-attributes --user-pool-id --username --user-attributes Name="email",Value="[email protected]"

Replace <existing_username> with the username of the existing user and [email protected] with the new alias.

3. Use a Different Alias

If you are creating a new user, consider using a different alias that is not already in use. Ensure that the new alias is unique within the user pool.

Additional Resources

For more information on managing users in Amazon Cognito, refer to the Amazon Cognito User Pools Documentation. You can also explore the Amazon Cognito FAQs for common questions and answers.

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