Zero-Drift Linux Server Hardening & Kernel Parameter Tuning for High-Concurrency Web Workloads

The Problem with Default Configurations

Default Linux server distributions are engineered for compatibility, not security or extreme throughput. A fresh Ubuntu or Debian instance leaves unused network protocols enabled, permits weak cryptographic ciphers, and restricts file descriptor limits to levels that fail under moderate DDOS or traffic surges.

Kernel Sysctl Tuning for High Throughput

Add the following to `/etc/sysctl.d/99-rubacore-hardening.conf`:

# Protect against SYN flood attacks
net.ipv4.tcp_syncookies = 1

# Disable IP source routing (prevents spoofing) net.ipv4.conf.all.accept_source_route = 0 net.ipv6.conf.all.accept_source_route = 0

# Ignore ICMP echo broadcasts net.ipv4.icmp_echo_ignore_broadcasts = 1

# Maximize file descriptor limits for edge proxies fs.file-max = 2097152 ```

Enforcing Strict SSH Key Policies

Disable all password authentication, root direct logins, and enforce Ed25519 keys:

PermitRootLogin no
PasswordAuthentication no
ChallengeResponseAuthentication no
UsePAM yes
AuthenticationMethods publickey
KbdInteractiveAuthentication no

Infrastructure as Code must treat servers as ephemeral and immutable. Hardening configs must be committed to git and applied automatically during provisioning.