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Docker-Aware Firewall Manager for Self-Hosters
A lightweight agent that runs alongside Docker and UFW/iptables, automatically detecting when containers would bypass host firewall rules and inserting correct DOCKER-USER chain rules. Prevents the silent exposure of containers on public interfaces that standard firewall guides never mention.
Why this matters
You run Docker containers on your Debian VPS and followed every UFW tutorial you could find. You think your firewall blocks everything except ports 80, 443, and your SSH port. But Docker's networking uses the iptables FORWARD chain, which completely bypasses UFW's rules. Your database container or admin panel could be exposed on the public interface right now and you would never know. The ufw status command shows everything is fine. Only by running iptables -S and understanding Docker's DNAT internals would you discover the problem. Standard guides never mention this, and there is no tool that warns you or fixes it automatically.
- · Built for Self-hosters and small teams running Docker containers on Linux servers with UFW firewalls who are unaware their containers bypass host firewall rules.
- · Most likely monetization: Freemium with paid Pro features.
The Pain · Narrative
You run Docker containers on your Debian VPS and followed every UFW tutorial you could find. You think your firewall blocks everything except ports 80, 443, and your SSH port. But Docker's networking uses the iptables FORWARD chain, which completely bypasses UFW's rules. Your database container or admin panel could be exposed on the public interface right now and you would never know. The ufw status command shows everything is fine. Only by running iptables -S and understanding Docker's DNAT internals would you discover the problem. Standard guides never mention this, and there is no tool that warns you or fixes it automatically.
Score Breakdown
Market Signal
Go-to-Market
Self-hosters running Docker containers with UFW on Debian/Ubuntu VPS who learned firewall basics from tutorials but do not know about Docker's iptables interaction
~50K-100K Docker+UFW users globally in the self-hosting and small business segment
Organic posts in self-hosting and Docker-focused communities with a technical blog post explaining the problem
$5/month for Pro alerts, free for basic detection
1000 free installs and 10 paid subscribers within 30 days
MVP Scope · 1–2 weeks
- Build a Python script that detects Docker containers, their port mappings, and cross-references against UFW/iptables rules to identify bypassed ports
- Implement DOCKER-USER chain rule generator that creates correct blocking rules for non-allowed ports
- Create a simple CLI interface to list exposed containers and apply fixes
- Write a technical blog post explaining the Docker-UFW bypass problem as content marketing
- Set up a GitHub repository with documentation and installation instructions
- Add real-time monitoring mode that watches for new container starts and alerts on unexpected port exposures
- Build a simple web dashboard showing container port exposure status at a glance
- Implement automated remediation mode that inserts DOCKER-USER rules when new containers start
- Create integration tests covering Docker with UFW, Docker with raw iptables, and Docker with firewalld
- Launch publicly with the blog post and community announcement
Differentiation
Why This Might Fail
Self-rebuttal — the most important trust signal
- 1The problem, while painful, has a known manual fix that advanced users apply once and forget, limiting the perceived value of an ongoing tool
- 2Docker networking changes across versions and storage drivers, creating maintenance burden disproportionate to the small subscription revenue
- 3The target market is a niche within a niche (Docker users who also use UFW and self-host), which may be too small to sustain a standalone product
Evidence Summary
How AI synthesized this insight — no verbatim quotes
One commenter provided a detailed account of two painful gotchas: installing iptables-persistent silently removing UFW, and Docker's DNAT bypassing UFW chains entirely to expose containers on public interfaces. They emphasized that no standard ufw guide mentions these issues and that ufw status gives a false sense of security. The comment was highly specific and technical, indicating this is a real but niche problem experienced by Docker self-hosters who rely on UFW.
Action Plan
Validate this opportunity before writing code
Recommended Next Step
Validate
Promising signals, but needs confirmation. Create a landing page, collect email sign-ups, then decide.
Landing Page Copy Kit
Ready-to-paste copy based on real Reddit community language — no editing required
Headline
Docker-Aware Firewall Manager for Self-Hosters
Sub-headline
A lightweight agent that runs alongside Docker and UFW/iptables, automatically detecting when containers would bypass host firewall rules and inserting correct DOCKER-USER chain rules. Prevents the silent exposure of containers on public interfaces that standard firewall guides never mention.
Who It's For
For Self-hosters and small teams running Docker containers on Linux servers with UFW firewalls who are unaware their containers bypass host firewall rules
Feature List
✓ Real-time detection of Docker containers that bypass UFW/iptables rules ✓ Automatic insertion of correct DOCKER-USER chain rules based on user-defined allowed ports ✓ Dashboard showing which container ports are exposed on public vs private interfaces ✓ Alerts when new containers start with exposed ports ✓ Integration with existing UFW configuration
Where to Validate
Share your landing page in r/r/selfhosted — that's exactly where these pain points were discovered.
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