Updating a Docker Application Safely (docker-compose)¶

This guide explains how to update a Dockerized application without losing data.
It applies to any container started using docker-compose.

Why Storage Can Be Lost (and How to Avoid It)¶

If your data lives inside a Docker container, updating will erase it

If you delete a container that contains its own data, that data is permanently removed.
Never store persistent information inside a container's internal filesystem.

To keep data safe, it must be mounted from the host:

volumes:
  - ./storage:/app/server/storage

Note

The path on the left (./storage) is on your filesystem.
Updating Docker containers will not delete this directory.

Confirm That Storage Is Mounted¶

Before updating, verify that your deployment actually mounts storage correctly.

docker inspect <container-name> | grep -i Source -A1

Expected example:

"Source": "/home/user/app/storage",
"Destination": "/app/server/storage"

If "Source" points to a local path, your data is safe.

Step-by-Step: Updating Using docker-compose¶

Tip

You must run these commands in the same folder where docker-compose.yml exists.
Running docker-compose elsewhere will not affect this service.

cd ~/app-folder
docker-compose pull
docker-compose down
docker-compose up -d

What these commands do¶

Command	Meaning
`docker-compose pull`	Downloads the newest version of the image
`docker-compose down`	Stops & removes the old container (but not your mounted data)
`docker-compose up -d`	Starts a new container using the updated image

Verify That the Update Worked¶

docker ps --format "table {{.Names}}\t{{.Image}}\t{{.Status}}"

Example

If your app exposes a UI, open it in a browser and check the version label.

Optional: Back Up Your Data (Extra Safety)¶

cp -a storage storage_backup_$(date +%Y%m%d)

Tip

This creates a full copy of your data folder. It is safe but optional before updates.

Clean Up Old Images (Reclaim Disk Space)¶

Once you've confirmed everything is working:

docker image prune -f

Or delete only unused images:

docker rmi $(docker images -f "dangling=true" -q)

Warning

Do not prune images before confirming the application starts and data is intact.

Multiple Docker Apps on One Server¶

Each app lives in its own folder.
To update one, you must cd into its directory:

~/anythingllm      → updating here affects AnythingLLM only
~/n8n              → updating here affects n8n only
~/myapp            → updating here affects only that app

TL;DR¶

cd ~/app-folder
docker-compose pull
docker-compose down
docker-compose up -d
# optional after confirming
docker image prune -f