There was a recent post about whether to enable ufw and it made me ask: how protected I am from a rogue docker container? I have a single server with 15-20 docker containers running at any given time. Should one get hacked or be malicious from the get go, are there (hopefully easy to implement for an armchair sysadmin) best practices to mitigate such an event? Thanks!
Only give the container access to the folders it needs for your application to operate as intended.
Only give the container access to the networks it needs for the application to run as intended.
Don’t run containers as root unless absolutely necessary.
Don’t expose an application to the Internet unless necessary. If you’re the only one accessing it remotely, or if you can manage any of the other devices that might (say, for family members), access your home network via a VPN. There are multiple ways to do this. I run a VPN server on my router. Tailscale is a good user-friendly option.
If you do need to expose an application to the Internet, don’t do so directly. Use a reverse proxy. One common setup: Put your containers on private networks (shared among multiple only in cases where they need to speak to each other), with ports forwarded from the containers to the host. Install a reverse proxy like Nginx Proxy Manager. Forward 80 and 443 from the router to NGM, but don’t forward anything else from the router. Register a domain, with subdomains for each service you use. Point the domain and subdomains to your IP, or using aliases, to a dynamic dns domain that connects to a service on your network (in my case, I use my Asus router’s DDNS service). Have NGM connect each subdomain to the appropriate port on the host (ie, nc.example.com going to a port on the hose being used for NextCloud). Have NGM handle SSL certificate requests and renewals.
There are other options that don’t involve any open ports, like Cloudflare tunnels. There are also other good reverse proxy options.
Consider using something like fail2ban or crowdsec to mitigate brute force attacks and ban bad actors. Consider something like Authentik for an extra layer of authentication. If you use Cloudflare, consider its DDOS protection and other security enhancements.
Keep good and frequent backups.
Don’t use the same password for multiple services, whether they’re ones you run or elsewhere.
Throw salt over your shoulder, say three Hail Marys and cross your fingers.