Does Flask Work With AWS?
Flask and AWS work together seamlessly—Flask runs on EC2, Lambda, App Runner, and other AWS services, with native AWS SDK integration.
Quick Facts
How Flask Works With AWS
Flask applications deploy across multiple AWS services depending on your needs. The most common approach is running Flask on EC2 instances with load balancing via ALB/NLB, but serverless deployment on Lambda is increasingly popular using frameworks like Zappa or AWS Lambda Web Adapter. For containerized deployments, Flask runs on ECS/Fargate behind ALB. AWS SDK integration is handled through boto3, which lets you interact with S3, DynamoDB, RDS, SQS, and other services directly from your Flask routes. The developer experience is straightforward: install boto3, configure IAM roles on your EC2 instance or Lambda execution role, and make API calls to AWS services. Architecture-wise, Flask stays stateless and delegates storage/sessions to AWS services like ElastiCache (Redis/Memcached) or DynamoDB. For traditional server deployments, use gunicorn/uWSGI behind an ALB with auto-scaling groups. Lambda deployments require packaging Flask with a WSGI adapter but offer better cost efficiency for variable workloads. Most developers find the learning curve minimal since Flask requires no AWS-specific modifications—it's just standard Python with boto3 calls.
Best Use Cases
Flask App with S3 Upload on AWS Lambda
pip install flask boto3 werkzeugfrom flask import Flask, request, jsonify
import boto3
import os
app = Flask(__name__)
s3_client = boto3.client('s3')
BUCKET_NAME = os.environ.get('S3_BUCKET')
@app.route('/upload', methods=['POST'])
def upload_file():
if 'file' not in request.files:
return jsonify({'error': 'No file part'}), 400
file = request.files['file']
if file.filename == '':
return jsonify({'error': 'No selected file'}), 400
try:
s3_client.put_object(
Bucket=BUCKET_NAME,
Key=file.filename,
Body=file.stream.read(),
ContentType=file.content_type
)
return jsonify({'message': f'File {file.filename} uploaded'}), 200
except Exception as e:
return jsonify({'error': str(e)}), 500
if __name__ == '__main__':
app.run(debug=True)Known Issues & Gotchas
Cold starts on Lambda can cause 5-15 second delays for first invocation after idle periods
Fix: Use Provisioned Concurrency, keep deployment packages small (<50MB), or use App Runner for warmer instances with automatic scaling
IAM permission errors at runtime because execution role lacks required service permissions
Fix: Attach least-privilege IAM policies to EC2 instance roles or Lambda execution roles; use AWS Systems Manager Parameter Store/Secrets Manager for credentials
Flask sessions don't persist across instances without external storage (in-memory sessions lost on restart)
Fix: Use ElastiCache for session storage or configure Flask to use DynamoDB via flask-session library
Lambda has 15-minute timeout limit and 512MB /tmp disk, breaking large file uploads or processing
Fix: Stream uploads directly to S3 using presigned URLs, or use EC2/Fargate for long-running tasks
Alternatives
- •FastAPI with AWS Lambda using Mangum (faster async framework, better for high-concurrency APIs)
- •Django with AWS Elastic Beanstalk (more batteries-included framework, better for complex applications)
- •Node.js/Express with AWS (non-Python alternative if team prefers JavaScript, similar AWS integration)
Resources
Related Compatibility Guides
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