Docker on a VPS: Limits, Networking and Persistent Data

Docker can package applications on a VPS, but you still need to manage the host, constrain resource use, audit published ports and back up persistent data. Replacing a container should not destroy the application’s state. Installing Docker also changes networking behavior, so review exposure instead of assuming an existing UFW policy covers every container port.

1. Install for the actual distribution

Identify the OS release and follow Docker’s supported repository instructions for that distribution. Avoid mixing packages from unrelated distributions or past tutorials. Verify the installed Engine and client versions. Treat access to a rootful Docker daemon as privileged host access; adding someone to its management group is not ordinary application access.

2. Begin with a loopback-only example

# Demonstration only: no public listener and no persistent application data
docker run -d --name preview-web --memory=256m --cpus=0.5 -p 127.0.0.1:8080:80 nginx:stable
curl http://127.0.0.1:8080
docker stats --no-stream preview-web
docker logs --tail 50 preview-web

The memory and CPU values are demonstration constraints, not production sizing advice. The stable tag can change; pin a tested release or digest for a reproducible deployment. This example serves the image’s default page and should not be treated as a configured application or a storage solution.

3. Audit exposure at every layer

Publishing a port without a specific host address can expose it on external interfaces. Docker’s packet-filtering rules can divert published-port traffic before ordinary UFW processing. Follow the documentation for the active firewall backend and verify access from an external host as well as locally.

A loopback-bound application can sit behind a deliberately configured reverse proxy, but that proxy introduces its own TLS and access rules. Keep database ports private to the services that need them. Do not expose the Docker API to the Internet as a shortcut to remote administration.

4. Separate images from persistent state

What survives which operation?
Item	Operational meaning
Image	Rebuildable application/runtime package; record the exact version
Container writable layer	Tied to that container; unsuitable as the only durable data plan
Named volume or bind mount	Persistent storage with ownership, backup and lifecycle responsibilities
Database data	Needs an application-consistent backup method, even inside a volume
Secrets/configuration	Must be supplied securely and recoverable independently of one container

Inventory the application’s actual data paths before mounting storage. A mount can hide files supplied in an image, and a wrong path can leave new data in the container layer while a backup job protects an empty volume. Verify where a test record is written and that it survives controlled container replacement.

5. Prove the deployment and restore procedure

Record the image digest, configuration, networks, published ports, limits and persistent mounts.
Exercise the application and check its resource peaks, including initialization and backup work.
Create a consistent backup of persistent data and configuration; stop writers where the backup method requires it.
Restore into separate volumes and an isolated instance, then verify representative records and restart behavior.
For an update, keep the previous image and a matched pre-migration data backup. An older image cannot always read a newer database schema.

Use VPS backups and secure administration alongside this checklist. Compare VPS capacity for the host and all containers together; containerization does not create additional physical resources.