Step-By-Step Guide: Accessing S3 objects via S3 Pre-signed URLs

Accessing S3 objects via S3 Pre-signed URLs generated using Python Flask Server deployed on Amazon Ec2 instance.

High-level Architecture

Step 0. Create an S3 bucket, copy the Image file and the code

a. Create an S3 bucket named pre-signed-url-bucket

b. Create a file pre_signed_url.py on your local with the following content

import os
import boto3

from flask import Flask, session, redirect, escape, request

# Create the pre-signed URL
def pre_signed_s3_url(bucket, key, expiration):
    """ Generate pre-signed URL on S3 (Default 1 hour expiration)
    """
    params = {
        'Bucket': bucket,
        'Key': key
    }
    s3 = boto3.client('s3')
    url = s3.generate_presigned_url('get_object', Params=params, ExpiresIn=expiration)
    return (url)

# Configure the application name with the FLASK_APP environment variable.
app = Flask(__name__)

# Configure the secret_key with the SECRET_KEY environment variable.
app.secret_key = os.environ.get('SECRET_KEY', default=None)

@app.route('/')
def index():
    pre_signed_url = pre_signed_s3_url('pre-signed-url-bucket', 'sample.png', 3660)
    html_out = '''<!DOCTYPE html> 
                    <html> 
                      <head> 
                        <title>
                           Pre-signed url Step-By-Step Guide  
                        </title>
                      </head>
                      <body>
                        <h1>Image from pre-signed URL</h1>
                        <img src= {0} alt="Pre-Signed URL generated image link"> 
                      </body>
                      </html>'''.format(pre_signed_url)

    return html_out

import os

import boto3

from flask import Flask, session, redirect, escape, request

# Create the pre-signed URL

def pre_signed_s3_url(bucket, key, expiration):

""" Generate pre-signed URL on S3 (Default 1 hour expiration)

"""

params = {

'Bucket': bucket,

'Key': key

}

s3 = boto3.client('s3')

url = s3.generate_presigned_url('get_object', Params=params, ExpiresIn=expiration)

return (url)

# Configure the application name with the FLASK_APP environment variable.

app = Flask(__name__)

# Configure the secret_key with the SECRET_KEY environment variable.

app.secret_key = os.environ.get('SECRET_KEY', default=None)

@app.route('/')

def index():

pre_signed_url = pre_signed_s3_url('pre-signed-url-bucket', 'sample.png', 3660)

html_out = '''<!DOCTYPE html>

<html>

<head>

<title>

Pre-signed url Step-By-Step Guide

</title>

</head>

<body>

<h1>Image from pre-signed URL</h1>

</body>

</html>'''.format(pre_signed_url)

return html_out

c. Copy the file pre_signed_url.py and the image sample.png to pre-signed-url-bucket

sample Download sample.png

Step 1. Launch an EC2 Instance

a. Launch an EC2 instance with the following config

Name: Flask Server

b. Create a Key pair with pem extension

c. Create a Security Group and a Security Group Rule to allow incoming SSH and Custom TCP (port 5000) traffic

d. Launch Instance

Step 2. Connect and Install Python and Virtualenv on E2 Instance

a. Connect to the EC2 Instance

c. Install Python and Virtualenv

sudo yum install python3
sudo yum install python3-pip
pip install virtualenv

sudo yum install python3

sudo yum install python3-pip

pip install virtualenv

Step 3. Copy the image file and the code from S3 to the EC2 instance

aws s3 cp s3://pre-signed-url-bucket/pre_signed_url.py pre_signed_url.py
aws s3 cp s3://pre-signed-url-bucket/sample.png sample.png

1 2	aws s3 cp s3://pre-signed-url-bucket/pre_signed_url.py pre_signed_url.py aws s3 cp s3://pre-signed-url-bucket/sample.png sample.png

Note

If you get “fatal error: Unable to locate credentials” try running the following and check the output

aws configure list

1	aws configure list

if the credentials are not set, set the credentials using the following command

aws configure

1	aws configure

Step 4. Run your Flask Web Application Server

virtualenv venv
source ./venv/bin/activate
# install boto3 library
pip3 install boto3
export FLASK_APP=pre_signed_url.py
export SECRET_KEY=0987654321
pip3 install flask
flask run -h 0.0.0.0 -p 5000 --reload

virtualenv venv

source ./venv/bin/activate

# install boto3 library

pip3 install boto3

export FLASK_APP=pre_signed_url.py

export SECRET_KEY=0987654321

pip3 install flask

flask run -h 0.0.0.0 -p 5000 --reload

Step 5. Access the Image from the browser

http://<your_ec2_instance_public_ip>:5000

Coddicted