How to efficiently allow for users to view Amazon S3 content? - amazon-web-services

Question

I am currently creating a basic app with React-Native (frontend) and Flask/MongoDB (backend). I am planning on using AWS S3 as cheap cloud storage for all the images and videos that are going to be uploaded and viewed. My current idea (and this could be totally off), is when a user uploads content, it will go through my Flask API and then to the S3 storage. When a user wants to view content, I am not sure what the plan of attack is here. Should I use my Flask API as a proxy, or is there a way to simply send a link to the content directly on S3 (which would avoid the extra traffic through my API)?
I am quite new to using AWS and if there is already a post discussing this topic, please let me know, and I'd be more than happy to take down this duplicate. I just can't seem to find anything.

Answer 1

Should I use my Flask API as a proxy, or is there a way to simply send a link to the content directly on S3 (which would avoid the extra traffic through my API)?
If the content is public, you just provide an URL which points directly to the file on the S3 bucket.
If the content is private, you generate presigned url on your backend for the file for which you want to give access. This URL should be valid for a short amount of time (for example: 15/30 minutes). You can regenerate it, if it becomes unavailable.
Moreover, you can generate a presigned URL which can be used for uploads directly from the front-end to the S3 bucket. This might be an option if you don't want the upload traffic to go through the backend or you want faster uploads.

Answer 2

There is an API boto3, try to use it.
It is not so difficult, I have done something similar, will post code here.
I have done like #Ervin said.
frontend asks backend to generate credentials
backend sends to frontend the credentials
Frontend upload file to S3
Frontend warns backend it has done.
Backend validate if everything is ok.
Backend will create a link to download, you have a lot of security options.
example of item 6) To generate a presigned url to download content.
bucket = app.config.get('BOTO3_BUCKET', None)
client = boto_flask.clients.get('s3')
params = {}
params['Bucket'] = bucket
params['Key'] = attachment_model.s3_filename
params['ResponseContentDisposition'] = 'attachment; filename={0}'.format(attachment_model.filename)
if attachment_model.mimetype is not None:
params['ResponseContentType'] = attachment_model.mimetype
url = client.generate_presigned_url('get_object', ExpiresIn=3600, Params=params)
example of item 2) Backend will create presigned credentials to post your file on S3, send s3_credentials to frontend
acl_permission = 'private' if private_attachment else 'public-read'
condition = [{'acl': acl_permission},
["starts-with", "$key", '{0}/'.format(folder_name)],
{'Content-Type': mimetype }]
bucket = app.config.get('BOTO3_BUCKET', None)
fields = {"acl": acl_permission, 'Bucket': bucket, 'Content-Type': mimetype}
client = boto_flask.clients.get('s3')
s3_credentials = client.generate_presigned_post(bucket, s3_filename, Fields=fields, Conditions=condition, ExpiresIn=3600)
example of item 5) Here are an example how backend can check if file on S3 are ok.
bucket = app.config.get('BOTO3_BUCKET', None)
client = boto_flask.clients.get('s3')
response = client.head_object(Bucket=bucket, Key=s3_filename)
if response is None:
return None, None
md5 = response.get('ETag').replace('"', '')
size = response.get('ContentLength')
Here are an example how frontend will ask for credentials, upload file to S3 and inform backend it is done.
I tried to remove a lot of particular code.
//frontend asking backend to create credentials, frontend will send some file metadata
AttachmentService.createPostUrl(payload).then((responseCredentials) => {
let form = new FormData();
Object.keys(responseCredentials.s3.fields).forEach(key => {
form.append(key, responseCredentials.s3.fields[key]);
});
form.append("file", file);
let payload = {
data: form,
url: responseCredentials.s3.url
}
//Frontend will send file to S3
axios.post(payload.url, payload.data).then((res) => {
return Promise.resolve(true);
}).then((result) => {
//when it is done, frontend informs backend
AttachmentService.uploadSuccess(...).then((refreshCase) => {
//Success
});
});
});