How to Deal With Multiple Uploads in Mobile Web App

In web and mobile applications, it's common to provide users with the ability to upload information. Your application may allow users to upload PDFs and documents, or media such every bit photos or videos. Every modernistic web server technology has mechanisms to allow this functionality. Typically, in the server-based environment, the procedure follows this catamenia:

1. The user uploads the file to the application server.
2. The application server saves the upload to a temporary space for processing.
3. The application transfers the file to a database, file server, or object store for persistent storage.

While the process is simple, it tin have significant side-effects on the performance of the web-server in busier applications. Media uploads are typically large, then transferring these tin represent a large share of network I/O and server CPU time. You must as well manage the state of the transfer to ensure that the unabridged object is successfully uploaded, and manage retries and errors.

This is challenging for applications with spiky traffic patterns. For example, in a web awarding that specializes in sending vacation greetings, information technology may experience near traffic only around holidays. If thousands of users attempt to upload media around the aforementioned time, this requires you lot to scale out the application server and ensure that there is sufficient network bandwidth bachelor.

By straight uploading these files to Amazon S3, yous can avoid proxying these requests through your application server. This can significantly reduce network traffic and server CPU usage, and enable your application server to handle other requests during busy periods. S3 also is highly available and durable, making information technology an ideal persistent store for user uploads.

In this blog post, I walk through how to implement serverless uploads and show the benefits of this arroyo. This pattern is used in the Happy Path web application. You can download the code from this blog post in this GitHub repo.

Overview of serverless uploading to S3

When yous upload straight to an S3 bucket, you must first request a signed URL from the Amazon S3 service. You can so upload directly using the signed URL. This is ii-stride process for your application front end end:

1. Call an Amazon API Gateway endpoint, which invokes the getSignedURL Lambda function. This gets a signed URL from the S3 bucket.
2. Directly upload the file from the application to the S3 bucket.

To deploy the S3 uploader example in your AWS account:

1. Navigate to the S3 uploader repo and install the prerequisites listed in the README.md.
2. In a terminal window, run:
   git clone https://github.com/aws-samples/amazon-s3-presigned-urls-aws-sam
cd amazon-s3-presigned-urls-aws-sam
sam deploy --guided

3. At the prompts, enter s3uploader for Stack Name and select your preferred Region. Once the deployment is consummate, note the APIendpoint output.The API endpoint value is the base of operations URL. The upload URL is the API endpoint with /uploads appended. For example: https://ab123345677.execute-api.us-west-ii.amazonaws.com/uploads.

Testing the application

I prove two ways to test this application. The first is with Postman, which allows you to direct call the API and upload a binary file with the signed URL. The second is with a bones frontend application that demonstrates how to integrate the API.

To test using Postman:

1. First, copy the API endpoint from the output of the deployment.
2. In the Postman interface, paste the API endpoint into the box labeled Enter request URL.
3. Choose Transport.
4. After the request is complete, the Torso section shows a JSON response. The uploadURL aspect contains the signed URL. Copy this aspect to the clipboard.
5. Select the + icon adjacent to the tabs to create a new asking.
6. Using the dropdown, modify the method from Go to PUT. Paste the URL into the Enter request URL box.
7. Cull the Body tab, and then the binary radio button.
8. Choose Select file and choose a JPG file to upload.
   Choose Send. You lot meet a 200 OK response after the file is uploaded.
9. Navigate to the S3 console, and open the S3 bucket created by the deployment. In the bucket, you lot see the JPG file uploaded via Postman.

To test with the sample frontend application:

1. Copy index.html from the instance'southward repo to an S3 bucket.
2. Update the object'southward permissions to make it publicly readable.
3. In a browser, navigate to the public URL of index.html file.
4. Select Choose file so select a JPG file to upload in the file picker. Choose Upload image. When the upload completes, a confirmation message is displayed.
5. Navigate to the S3 console, and open up the S3 bucket created past the deployment. In the saucepan, yous run across the 2d JPG file you uploaded from the browser.

Understanding the S3 uploading process

When uploading objects to S3 from a web awarding, you lot must configure S3 for Cross-Origin Resource Sharing (CORS). CORS rules are defined as an XML document on the bucket. Using AWS SAM, you tin configure CORS as part of the resource definition in the AWS SAM template:

                      S3UploadBucket:     Type: AWS::S3::Bucket     Backdrop:       CorsConfiguration:         CorsRules:         - AllowedHeaders:             - "*"           AllowedMethods:             - GET             - PUT             - HEAD           AllowedOrigins:             - "*"                  

The preceding policy allows all headers and origins – it'due south recommended that you lot apply a more restrictive policy for production workloads.

In the beginning step of the procedure, the API endpoint invokes the Lambda function to make the signed URL request. The Lambda part contains the following code:

          const AWS = require('aws-sdk') AWS.config.update({ region: process.env.AWS_REGION }) const s3 = new AWS.S3() const URL_EXPIRATION_SECONDS = 300  // Main Lambda entry point exports.handler = async (event) => {   return await getUploadURL(event) }  const getUploadURL = async function(result) {   const randomID = parseInt(Math.random() * 10000000)   const Key = `${randomID}.jpg`    // Become signed URL from S3   const s3Params = {     Bucket: process.env.UploadBucket,     Key,     Expires: URL_EXPIRATION_SECONDS,     ContentType: 'prototype/jpeg'   }   const uploadURL = await s3.getSignedUrlPromise('putObject', s3Params)   return JSON.stringify({     uploadURL: uploadURL,     Key   }) }                  

This function determines the proper name, or central, of the uploaded object, using a random number. The s3Params object defines the accepted content type and as well specifies the expiration of the key. In this case, the key is valid for 300 seconds. The signed URL is returned as office of a JSON object including the key for the calling awarding.

The signed URL contains a security token with permissions to upload this single object to this bucket. To successfully generate this token, the code calling getSignedUrlPromise must have s3:putObject permissions for the bucket. This Lambda part is granted the S3WritePolicy policy to the bucket by the AWS SAM template.

The uploaded object must match the same file proper noun and content type as defined in the parameters. An object matching the parameters may be uploaded multiple times, providing that the upload procedure starts before the token expires. The default expiration is 15 minutes but you may want to specify shorter expirations depending upon your utilize case.

Once the frontend application receives the API endpoint response, information technology has the signed URL. The frontend application so uses the PUT method to upload binary information directly to the signed URL:

          let blobData = new Hulk([new Uint8Array(array)], {type: 'image/jpeg'}) const result = await fetch(signedURL, {   method: 'PUT',   body: blobData })                  

At this signal, the caller awarding is interacting directly with the S3 service and non with your API endpoint or Lambda function. S3 returns a 200 HTML condition code once the upload is complete.

For applications expecting a big number of user uploads, this provides a simple way to offload a big corporeality of network traffic to S3, away from your backend infrastructure.

Adding authentication to the upload process

The current API endpoint is open, available to whatever service on the net. This means that anyone can upload a JPG file in one case they receive the signed URL. In most product systems, developers want to utilize authentication to control who has admission to the API, and who can upload files to your S3 buckets.

You can restrict admission to this API past using an authorizer. This sample uses HTTP APIs, which back up JWT authorizers. This allows you lot to control access to the API via an identity provider, which could be a service such as Amazon Cognito or Auth0.

The Happy Path awarding simply allows signed-in users to upload files, using Auth0 as the identity provider. The sample repo contains a 2d AWS SAM template, templateWithAuth.yaml, which shows how you can add together an authorizer to the API:

                      MyApi:     Type: AWS::Serverless::HttpApi     Properties:       Auth:         Authorizers:           MyAuthorizer:             JwtConfiguration:               issuer: !Ref Auth0issuer               audition:                 - https://auth0-jwt-authorizer             IdentitySource: "$request.header.Say-so"         DefaultAuthorizer: MyAuthorizer                  

Both the issuer and audition attributes are provided by the Auth0 configuration. By specifying this authorizer equally the default authorizer, it is used automatically for all routes using this API. Read part 1 of the Ask Around Me serial to learn more about configuring Auth0 and authorizers with HTTP APIs.

Later on authentication is added, the calling web application provides a JWT token in the headers of the request:

          const response = await axios.become(API_ENDPOINT_URL, {   headers: {     Authorization: `Bearer ${token}`         } })                  

API Gateway evaluates this token before invoking the getUploadURL Lambda function. This ensures that only authenticated users tin can upload objects to the S3 bucket.

Modifying ACLs and creating publicly readable objects

In the current implementation, the uploaded object is not publicly attainable. To make an uploaded object publicly readable, y'all must set up its access control list (ACL). At that place are preconfigured ACLs bachelor in S3, including a public-read option, which makes an object readable by anyone on the internet. Set the advisable ACL in the params object before calling s3.getSignedUrl:

          const s3Params = {   Bucket: process.env.UploadBucket,   Cardinal,   Expires: URL_EXPIRATION_SECONDS,   ContentType: 'image/jpeg',   ACL: 'public-read' }                  

Since the Lambda function must have the appropriate bucket permissions to sign the asking, you must too ensure that the function has PutObjectAcl permission. In AWS SAM, you tin can add the permission to the Lambda function with this policy:

                      - Statement:           - Event: Allow             Resource: !Sub 'arn:aws:s3:::${S3UploadBucket}/'             Action:               - s3:putObjectAcl                  

Conclusion

Many web and mobile applications allow users to upload data, including large media files like images and videos. In a traditional server-based application, this can create heavy load on the application server, and besides apply a considerable amount of network bandwidth.

By enabling users to upload files to Amazon S3, this serverless pattern moves the network load away from your service. This can brand your application much more scalable, and capable of treatment spiky traffic.

This blog postal service walks through a sample application repo and explains the process for retrieving a signed URL from S3. It explains how to the test the URLs in both Postman and in a spider web application. Finally, I explain how to add hallmark and make uploaded objects publicly accessible.

To learn more, see this video walkthrough that shows how to upload directly to S3 from a frontend web awarding. For more than serverless learning resources, visit https://serverlessland.com.

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Source: https://aws.amazon.com/blogs/compute/uploading-to-amazon-s3-directly-from-a-web-or-mobile-application/

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