why is my app losing files after container restart

If your app “loses files” after a container restart, the most common reason is that the files were stored inside the container’s writable layer, which is ephemeral. When the container is recreated or restarted, that layer may be reset or replaced.

Common causes

1) Files are written only inside the container filesystem

Containers are meant to be disposable. Anything saved to paths like:

• /tmp
• app working directories
• /var/app/data inside the container

will disappear if the container is removed and recreated, or sometimes if the runtime replaces the container.

2) No volume or bind mount is attached

If you want files to survive restarts, you need to store them on:

• a Docker volume
• a bind mount
• external storage like S3, NFS, EBS, Azure Disk, etc.

Example Docker volume:

docker run -v mydata:/data myimage

Example bind mount:

docker run -v /host/path:/data myimage

3) The container is being recreated, not just restarted

A true restart usually keeps the container filesystem, but orchestration tools often:

• stop the old container
• create a new one

Examples:

• Docker Compose recreating containers
• Kubernetes restarting pods
• ECS replacing tasks
• Cloud Run creating fresh instances

In those cases, files not on persistent storage are lost.

4) The app writes to the wrong path

You may have mounted persistent storage, but your app is saving files somewhere else, such as:

• a different directory
• a temp folder
• a path configured differently in production

5) Permissions or cleanup scripts remove files

Less common, but possible:

• startup scripts clean directories
• log rotation or app cleanup jobs delete files
• permissions prevent proper writes, leading to partial persistence issues

How to check

• Inspect where the app saves files
• Verify whether that path is mounted as a volume
• Check if your platform recreates containers/pods on restart
• Confirm the data directory exists on persistent storage
• Test by creating a file, restarting, and checking whether it’s still on the mounted volume

What to do

• Store persistent files outside the container filesystem
• Use a mounted volume or external storage
• Make sure the app writes to that mounted path
• For Kubernetes, use a PersistentVolumeClaim
• For Docker, use a named volume or bind mount

Example

If your app writes to /app/uploads, but you didn’t mount anything there:

docker run myimage

Those uploads will vanish when the container is replaced.

Fix:

docker run -v uploads:/app/uploads myimage

If you want, I can help you debug this for your specific setup — Docker, Docker Compose, Kubernetes, ECS, etc.