Efficiently Handling Large File Uploads (PDF/DOCX) in AWS

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Large file uploads are one of those things that look simple — until they crash your system. A few heavy PDFs or DOCX files can slow APIs, overload memory, and frustrate users faster than bad UX. We faced this exact challenge while managing document uploads in AWS, and what we learned changed the way we handle big files forever.

The Challenge

Large files don’t move through networks smoothly. Uploading them directly through the backend causes:

Timeouts due to long upload durations
Server memory overload as files get buffered
Failed uploads from unstable connections
Duplicate storage when retries don’t clear old files

The solution wasn’t “stronger servers.” It was smarter upload handling.

AWS Multipart Upload — The Real Game Changer

AWS S3 includes a built-in system called Multipart Upload — designed exactly for large files. Here’s what it does:

Splits one large file into smaller chunks (parts)
Uploads all parts independently and in parallel
Retries only the failed parts instead of restarting the whole upload
Automatically combines all parts into a single file after completion

This one feature fixed 90% of our upload issues.

How It Improved Performance

Uploads became faster and more stable, even for 100MB+ files
Uploads could resume from where they stopped if a connection dropped
No more API timeouts since uploads didn’t depend on a single long request
AWS validated file integrity for each part automatically

Result: fewer errors, less bandwidth waste, and smoother user experience.

Security & Data Integrity

While optimizing performance, we also focused on security:

Always upload over HTTPS to protect files in transit
Use Server-Side Encryption (SSE-S3 or SSE-KMS) for stored files
Set size limits and allowed MIME types to prevent unsafe uploads
Restrict upload permissions using AWS IAM roles or policies

Cost & Storage Optimization

Efficient uploads are also about saving costs:

Enable S3 Intelligent-Tiering to automatically move older files to cheaper storage
Set lifecycle rules to delete incomplete uploads
Encourage compression before uploading (especially for PDFs and DOCX)
Track upload costs with AWS CloudWatch metrics

Key Takeaways

Always use Multipart Upload for files larger than 5 MB
Compress before uploading
Encrypt during and after transfer
Clean up unfinished uploads
Monitor performance and costs regularly

Uploading large files isn’t about brute force — it’s about balance between speed, reliability, and cost-efficiency.

Jump into our new LinkedIn thread on — How to Handle Large File Uploads (PDF/DOCX) Efficiently in AWS
Also, read our last article: Designing Apps That Respect Your Phone Battery