An automated defensive baseline toolkit for locking down newly provisioned Linux hosts, SSH access, firewall policies, kernel network parameters, and container daemons.
Every new VPS or bare-metal node faces automated internet background scanning within seconds of coming online. Sentinel packages repeatable, idempotent defensive configurations and read-only posture audits used across personal and venture lab environments.
Default cloud images prioritize convenience over defense — leaving password authentication active, permissive network sysctls, unmonitored auth logs, and Docker port-binding pitfalls.
Compiled an auditable, non-destructive baseline workflow with dry-run verification, rollback backups, SSH key-only enforcement, default-deny firewall rules, and Docker daemon isolation checks.
Defensive infrastructure baseline used in authorized server setups and lab environments.
Runs an initial read-only posture audit before applying reversible, backed-up configuration layers across auth, network, kernel, and runtime surfaces.
Produces a baseline report without mutating host files during dry-run inspection.
Validates active key access in a secondary check before reloading `sshd`.
Shrinks exposed network surface and hardens TCP/IP stack defaults.
Prevents Docker port leaks around host firewalls and maintains patch cadence.
Docker manipulates `iptables` directly and can expose container ports despite `UFW` rules.
DECISION: Enforced `127.0.0.1:PORT` loopback bindings behind reverse proxies and audited raw socket bindings.
OUTCOME: Consistent edge TLS and firewall enforcement across all containerized web services.
Aggressive hardening scripts can lock out operators on cloud consoles without serial access.
DECISION: Built mandatory syntax validation (`sshd -t`) and active key verification prior to service reload.
OUTCOME: Safe, repeatable provisioning across cloud and virtualized lab nodes.
Defensive security is mostly disciplined fundamentals executed consistently — not exotic tooling.
Understanding how Linux networking interacts with Docker bridges prevents one of the most common self-hosting misconfigurations.
