S3

Introduction

S3 (Simple Storage Service) is an object storage service that provides a highly scalable and durable solution for storing and retrieving data. In S3, a bucket represents a directory, while an object corresponds to a file. Each object or file within S3 encompasses essential attributes such as a unique key denoting its name, the actual content it holds, a version ID for versioning support, and accompanying metadata. S3 can store unlimited objects, allowing you to store, retrieve, and manage your data in a highly adaptable and reliable manner.

LocalStack supports S3 via the Community offering, allowing you to use the S3 APIs in your local environment to create new buckets, manage your S3 objects, and test your S3 configurations locally. The supported APIs are available on our API coverage page, which provides information on the extent of S3’s integration with LocalStack.

Getting started

This guide is designed for users new to S3 and assumes basic knowledge of the AWS CLI and our awslocal wrapper script.

Start your LocalStack container using your preferred method. We will demonstrate how you can create an S3 bucket, manage S3 objects, and generate pre-signed URLs for S3 objects.

Create an S3 bucket

You can create an S3 bucket using the CreateBucket API. Run the following command to create an S3 bucket named sample-bucket:

$ awslocal s3api create-bucket --bucket sample-bucket

You can list your S3 buckets using the ListBuckets API. Run the following command to list your S3 buckets:

$ awslocal s3api list-buckets

On successful creation of the S3 bucket, you will see the following output:

{
    "Buckets": [
        {
            "Name": "sample-bucket",
            "CreationDate": "2023-07-18T06:36:25+00:00"
        }
    ],
    "Owner": {
        "DisplayName": "webfile",
        "ID": "75aa57f09aa0c8caeab4f8c24e99d10f8e7faeebf76c078efc7c6caea54ba06a"
    }
}

Managing S3 objects

To upload a file to your S3 bucket, you can use the PutObject API. Download a random image from the internet and save it as image.jpg. Run the following command to upload the file to your S3 bucket:

$ awslocal s3api put-object \
  --bucket sample-bucket \
  --key image.jpg \
  --body image.jpg

You can list the objects in your S3 bucket using the ListObjects API. Run the following command to list the objects in your S3 bucket:

$ awslocal s3api list-objects \
  --bucket sample-bucket

If your image has been uploaded successfully, you will see the following output:

{
    "Contents": [
        {
            "Key": "image.jpg",
            "LastModified": "2023-07-18T06:40:07+00:00",
            "ETag": "\"d41d8cd98f00b204e9800998ecf8427e\"",
            "Size": 0,
            "StorageClass": "STANDARD",
            "Owner": {
                "DisplayName": "webfile",
                "ID": "75aa57f09aa0c8caeab4f8c24e99d10f8e7faeebf76c078efc7c6caea54ba06a"
            }
        }
    ]
}

Run the following command to upload a file named index.html to your S3 bucket:

$ awslocal s3api put-object --bucket sample-bucket --key index.html --body index.html

{
    "ETag": "\"d41d8cd98f00b204e9800998ecf8427e\""
}

Generate a pre-signed URL for S3 object

You can generate a pre-signed URL for your S3 object using the presign command. Pre-signed URL allows anyone to retrieve the S3 object with an HTTP GET request.

Run the following command to generate a pre-signed URL for your S3 object:

$ awslocal s3 presign s3://sample-bucket/image.jpg

You will see a generated pre-signed URL for your S3 object. You can use cURL or wget to retrieve the S3 object using the pre-signed URL.

Path-Style and Virtual Hosted-Style Requests

Similar to AWS, LocalStack categorizes requests as either Path style or Virtual-Hosted style based on the Host header of the request. The following example illustrates this distinction:

http://<bucket-name>.s3.<region>.localhost.localstack.cloud:4566/<key-name> # host-style request
http://<bucket-name>.s3.localhost.localstack.cloud:4566/<key-name> # host-style request, region is not mandatory in LocalStack
http://s3.<region>.localhost.localstack.cloud:4566/<bucket-name>/<key-name> # path-style request
http://localhost:4566/<bucket-name>/<key-name> # path-style request

A Virtual-Hosted style request will have the bucket as part of the Host header of your request. In order for LocalStack to be able to parse the bucket name from your request, your endpoint needs to be prefixed with s3., like s3.localhost.localstack.cloud.

If your endpoint cannot be prefixed with s3., you should configure your SDK to use Path style request instead, and make the bucket part of the path.

By default, most SDKs will try to use Virtual-Hosted style requests and prepend your endpoint with the bucket name. However, if the endpoint is not prefixed by s3., LocalStack will not be able to understand the request and it will most likely result in an error.

You can either change the endpoint to an S3-specific one, or configure your SDK to use Path style requests instead. Check out our SDK documentation to learn how you can configure language SDKs to access LocalStack and S3.

If your endpoint is not prefixed with s3., all requests are treated as Path style requests. Using the s3.localhost.localstack.cloud endpoint URL is recommended for all requests aimed at S3.

Configuring Cross-Origin Resource Sharing on S3

You can configure Cross-Origin Resource Sharing (CORS) on a LocalStack S3 bucket using AWS Command Line Interface (CLI). It would allow your local application to communicate directly with an S3 bucket in LocalStack. By default, LocalStack will apply specific CORS rules to all requests to allow you to display and access your resources through LocalStack Web Application. If no CORS rules are configured for your S3 bucket, LocalStack will apply default rules unless specified otherwise.

To configure CORS rules for your S3 bucket, you can use the awslocal wrapper. Optionally, you can run a local web application on localhost:3000. You can emulate the same behaviour with an AWS SDK or an integration you use. Follow this step-by-step guide to configure CORS rules on your S3 bucket.

Run the following command on your terminal to create your S3 bucket:

$ awslocal s3api create-bucket --bucket cors-bucket
{
    "Location": "/cors-bucket"
}

Next, create a JSON file with the CORS configuration. The file should have the following format:

{
  "CORSRules": [
    {
      "AllowedHeaders": ["*"],
      "AllowedMethods": ["GET", "POST", "PUT"],
      "AllowedOrigins": ["http://localhost:3000"],
      "ExposeHeaders": ["ETag"]
    }
  ]
}

Save the file locally with a name of your choice, for example, cors-config.json. Run the following command to apply the CORS configuration to your S3 bucket:

$ awslocal s3api put-bucket-cors --bucket cors-bucket --cors-configuration file://cors-config.json

You can further verify that the CORS configuration was applied successfully by running the following command:

$ awslocal s3api get-bucket-cors --bucket cors-bucket

On applying the configuration successfully, you should see the same JSON configuration file you created earlier. Your S3 bucket is configured to allow cross-origin resource sharing, and if you try to send requests from your local application running on localhost:3000, they should be successful.

However, if you try to access your bucket from LocalStack Web Application, you’ll see errors, and your bucket won’t be accessible anymore. We can edit the JSON file cors-config.json you created earlier with the following configuration and save it:

{
  "CORSRules": [
    {
      "AllowedHeaders": ["*"],
      "AllowedMethods": ["GET", "POST", "PUT", "HEAD", "DELETE"],
      "AllowedOrigins": [
        "http://localhost:3000",
        "https://app.localstack.cloud",
        "http://app.localstack.cloud"
      ],
      "ExposeHeaders": ["ETag"]
    }
  ]
}

You can now run the same steps as before to update the CORS configuration and verify if it is applied correctly:

$ awslocal s3api put-bucket-cors --bucket cors-bucket --cors-configuration file://cors-config.json
$ awslocal s3api get-bucket-cors --bucket cors-bucket

You can try again to upload files in your bucket from the LocalStack Web Application and it should work.

Resource Browser

The LocalStack Web Application provides a Resource Browser for managing S3 buckets & configurations. You can access the Resource Browser by opening the LocalStack Web Application in your browser, navigating to the Resources section, and then clicking on S3 under the Storage section.

The Resource Browser allows you to perform the following actions:

• Create Bucket: Create a new S3 bucket by specifying a Bucket Name, Bucket Configuration, ACL, Object Ownership, and more.
• Objects & Permissions: View, upload, download, and delete objects in your S3 buckets. You can also view and edit the permissions, like the CORS Configuration for the bucket.
• Create Folder: Create a new folder in your S3 bucket by clicking on the Create Folder button and specifying a Folder Name.
• Delete Bucket: Delete an S3 bucket by selecting the S3 bucket and clicking on Actions button and clicking on Remove Selected.

Examples

The following code snippets and sample applications provide practical examples of how to use S3 in LocalStack for various use cases:

• Full-Stack application with Lambda, DynamoDB & S3 for shipment validation.
• Serverless Transcription application using Transcribe, S3, Lambda, SQS, and SES
• Query data in S3 Bucket with Amazon Athena, Glue Catalog & CloudFormation
• Serverless Image Resizer with Lambda, S3, SNS, and SES
• Host a static website locally using Simple Storage Service (S3) and Terraform with LocalStack