How do I set up shared storage for a web app that writes documents and images?

Shared storage for a web app usually means a place where all app instances can read/write the same files, such as uploaded images, generated documents, or user attachments.

Common options

1. Object storage

Best for most web apps.

Examples:

• AWS S3
• Google Cloud Storage
• Azure Blob Storage
• MinIO

Why it’s good:

• Works across multiple servers/containers
• Scales well
• Durable and easy to back up
• Great for images/documents

Typical setup:

1. Your app uploads files to object storage.
2. Store only the file metadata/URL in your database.
3. Serve files via:
   • public buckets for public assets, or
   • signed URLs for private files.

2. Network file share

Good if your app expects a normal filesystem.

Examples:

• NFS
• SMB/CIFS
• EFS (AWS), Filestore (GCP), Azure Files

Why it’s good:

• Mounts like a directory on each app server
• Easy if your app uses file paths directly

Caveats:

• Can be slower or more fragile than object storage
• Need to manage permissions and locking carefully
• Less ideal for many small writes or highly distributed setups

---

Recommended architecture

For most modern web apps:

• Documents/images: object storage
• Metadata: database
• Processing: app or worker generates files, uploads them, and records the location

Example flow:

1. User uploads an image.
2. Web app validates it.
3. App uploads it to S3/GCS.
4. App saves a record in the DB:
   • file key
   • MIME type
   • size
   • owner/user ID
   • timestamps
5. Frontend loads the file using a public URL or a signed URL.

---

If you need a shared filesystem

If your app requires local file paths, mount shared storage on every instance:

Example with NFS

• Create an NFS server or managed NFS service
• Mount it at the same path on all web servers, e.g. /var/app/uploads
• Ensure:
  • same user/group ownership
  • correct permissions
  • consistent backup strategy
  • file locking if multiple processes can write the same file

---

Important design tips

• Don’t store files in the app container’s local disk if you have multiple instances or autoscaling.
• Use unique filenames to avoid collisions, e.g. UUIDs.
• Validate uploads:
  • file type
  • size
  • content scanning if needed
• Keep originals and generated versions separate
• Consider lifecycle rules for old files and temporary uploads
• Back up metadata and storage
• Use CDN for public images if performance matters

---

Simple decision guide

Choose:

• S3/GCS/Azure Blob if you want scalability and reliability
• NFS/EFS/Azure Files if your app needs filesystem semantics
• Local disk only for development or single-server deployments

If you want, I can give you:

1. a setup example for AWS S3,
2. a Docker/Kubernetes shared volume example, or
3. a code example in Node.js, Python, or PHP.