Understanding AWS CLI S3 Presigned URLs

In the world of cloud computing, Amazon Web Services (AWS) is a dominant force, offering a wide range of services to help businesses and developers build scalable and efficient applications. One of the most popular services is Amazon S3 (Simple Storage Service), which provides secure, durable, and highly scalable object storage. The AWS Command - Line Interface (CLI) is a powerful tool that allows users to interact with AWS services from the command line. In this blog post, we will focus on AWS CLI S3 presigned URLs, explaining what they are, their typical usage scenarios, common practices, and best practices.

Table of Contents#

  1. What are AWS CLI S3 Presigned URLs?
  2. Typical Usage Scenarios
  3. Common Practices
  4. Best Practices
  5. Conclusion
  6. FAQ
  7. References

Article#

What are AWS CLI S3 Presigned URLs?#

A presigned URL is a URL that gives you temporary access to an Amazon S3 object. When you generate a presigned URL using the AWS CLI, you are essentially creating a time - limited link that allows anyone with the link to access the specified S3 object. The URL includes a signature, which is generated based on your AWS security credentials (access key and secret access key), the bucket name, the object key, and an expiration time.

Here is an example of how to generate a presigned URL using the AWS CLI:

aws s3 presign s3://my - bucket/my - object.txt --expires - in 3600

In this example, we are generating a presigned URL for the object my - object.txt in the bucket my - bucket that will expire in 3600 seconds (1 hour).

Typical Usage Scenarios#

Sharing Private Objects#

Amazon S3 buckets can be configured to be private, which means that only authorized users can access the objects stored in them. However, there are times when you need to share a private object with someone who does not have AWS credentials. A presigned URL allows you to do this securely and temporarily. For example, a content creator might want to share a private video stored in an S3 bucket with a client for a limited time.

Direct Uploads from Clients#

Instead of uploading files to your server first and then transferring them to S3, you can generate a presigned URL and allow clients to upload files directly to S3. This reduces the load on your server and speeds up the upload process. For example, a mobile app might use a presigned URL to upload user - generated content, such as photos or videos, directly to an S3 bucket.

Common Practices#

Expiration Time#

When generating a presigned URL, it is important to set an appropriate expiration time. If the expiration time is too long, there is a risk that the URL could be misused. If it is too short, the recipient might not have enough time to access the object. A good practice is to set the expiration time based on the specific use case. For example, if you are sharing a file for a one - time viewing, a few hours or a day might be sufficient.

Error Handling#

When using presigned URLs, it is important to handle errors properly. For example, if the URL has expired or the object has been deleted, the recipient will receive an error when trying to access the object. Your application should be able to handle these errors gracefully and provide appropriate feedback to the user.

Best Practices#

Security#

Always use AWS Identity and Access Management (IAM) policies to control who can generate presigned URLs. Only authorized users or applications should be able to generate these URLs. Additionally, make sure that your AWS security credentials are kept secure. Do not hard - code your access key and secret access key in your application code.

Monitoring and Logging#

Monitor the usage of presigned URLs to detect any abnormal activity. You can use AWS CloudTrail to log all API calls related to S3 presigned URL generation and access. This will help you identify any potential security issues and troubleshoot problems.

Conclusion#

AWS CLI S3 presigned URLs are a powerful and flexible tool for sharing private S3 objects and enabling direct uploads from clients. By understanding the core concepts, typical usage scenarios, common practices, and best practices, software engineers can use presigned URLs effectively and securely in their applications.

FAQ#

Q1: Can I generate a presigned URL for a folder in an S3 bucket?#

A: No, Amazon S3 does not have a true folder concept. Folders are just a naming convention. You can generate presigned URLs for individual objects, but not for a "folder".

Q2: What happens if the presigned URL is shared with unauthorized users?#

A: If the URL is still valid, unauthorized users will be able to access the object. That's why it's important to set an appropriate expiration time and use proper security measures.

Q3: Can I revoke a presigned URL before it expires?#

A: No, once a presigned URL is generated, it cannot be revoked. You can, however, delete the object from the S3 bucket, which will make the URL invalid.

References#

2025-10