upload files to aws s3 bucket with flask

upload-to-aws-flask.md

Upload files to AWS

Make sure you already have S3 bucket, access key and secret key before go through this notes.

How to connect to AWS?

Boto3 allows Python developers to write software that makes use of services like Amazon S3 and Amazon EC2.

Step 1: Install boto3 with pip

pip install boto3

Step 2: Configuration to connect to your S3 bucket

Make sure you store your S3 bucket, access key and secret key in your .env file, so that it won't be uploaded to github.

# in .env file

AWS_BUCKET_NAME=your_bucket_name
AWS_ACCESS_KEY=your_access_key
AWS_SECRET_ACCESS_KEY=your_secret_access_key
AWS_DOMAIN=http://your_bucket_name.s3.amazonaws.com/

Step 3: Display Form

Show your form in your html:

<form action="{{url_for('create')}}" method="POST" enctype="multipart/form-data">

    <label for="user_file">Upload Your File</label>
    <br>
    <input type="file" name="user_file">
    <br>
    <button type="submit">Upload</button>

</form>

Step 4: Make connection to AWS

Create a helpers.py in your util folder. Then use boto3 to establish a connection to the S3 service.

# in util/helpers.py

import boto3, botocore

s3 = boto3.client(
    "s3",
    aws_access_key_id=os.getenv('AWS_ACCESS_KEY'),
    aws_secret_access_key=os.getenv('AWS_SECRET_ACCESS_KEY')
)

After connected to S3, create a function to upload the file directly to the respective bucket. We'll use boto3.client.upload_fileobj provided by boto3, and this method accepts file and a bucket_name as arguments.

Files uploaded to a S3 bucket can be accessed via a public URL that usually looks like this:

https://nextagram-backend.s3.amazonaws.com/nextagram.jpg
https://<bucket_name>.s3.amazonaws.com/<filename>.<extension>

So, instead of saving the complete URL to database, we save the filename in our database in case we going to change the AWS bucket name due to deployment.

# in util/helpers.py

import os
from werkzeug.utils import secure_filename

def upload_file_to_s3(file, acl="public-read"):
    filename = secure_filename(file.filename)
    try:
        s3.upload_fileobj(
            file,
            os.getenv("AWS_BUCKET_NAME"),
            file.filename,
            ExtraArgs={
                "ACL": acl,
                "ContentType": file.content_type
            }
        )

    except Exception as e:
        # This is a catch all exception, edit this part to fit your needs.
        print("Something Happened: ", e)
        return e
    

    # after upload file to s3 bucket, return filename of the uploaded file
    return file.filename

Step 5: Call upload function

Now you have a function to upload to bucket, we will then import and call it in the upload route. Before uploading the file, we need to do some checkings to make sure the file submitted from the form is valid file format.

# views.py

from flask import render_template, request, redirect, url_for
from instagram_web.util.helpers import upload_file_to_s3

ALLOWED_EXTENSIONS = {'png', 'jpg', 'jpeg', 'gif'}

# function to check file extension
def allowed_file(filename):
    return '.' in filename and \
        filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS

@app.route("/upload", methods=["POST"])
def create():

    # check whether an input field with name 'user_file' exist
    if 'user_file' not in request.files:
        flash('No user_file key in request.files')
        return redirect(url_for('new'))

    # after confirm 'user_file' exist, get the file from input
    file = request.files['user_file']

    # check whether a file is selected
    if file.filename == '':
        flash('No selected file')
        return redirect(url_for('new'))

    # check whether the file extension is allowed (eg. png,jpeg,jpg,gif)
    if file and allowed_file(file.filename):
        output = upload_file_to_s3(file) 
        
        # if upload success,will return file name of uploaded file
        if output:
            # write your code here 
            # to save the file name in database

            flash("Success upload")
            return redirect(url_for('show'))

        # upload failed, redirect to upload page
        else:
            flash("Unable to upload, try again")
            return redirect(url_for('new'))
        
    # if file extension not allowed
    else:
        flash("File type not accepted,please try again.")
        return redirect(url_for('new'))

At last we save the filename return from upload_file_to_s3 into the database.

Hi, how did you test the Exception for upload_file?

@simanacci You can actually mock s3.upload_fileobj

Here is the snippet code you can use:

# test_helpers.py
from unittest import mock

@mock.patch("util.helpers.s3")
def test_helpers(mocked_s3):
    mocked_s3.upload_fileobj.side_effect = Exception("error_message")

    ... put your assertions here

Hope this helpful for you!

Hi,
I'm looking for a way to upload big files to S3 from flask, using boto3 (or any other s3 interface). Using Dropzone you can specify chunking and parallel uploads. I'm trying to figure out of it now, but it's complex material. You don't happen to have done that already? (and if so, do you have the possibility to share the code?)