Hardened Debian 12 Server

Charges for this image cover the security hardening, optimization, and pre-integration work Hanwei performs on top of the upstream Debian 12 project. No application software is added. What the image carries is the configuration work: a hardened SSH and kernel baseline, resource ceilings raised for server workloads, auditd rules for privileged command tracing, Systems Manager and Amazon Time Sync integration, and automatic root filesystem expansion. This version supersedes the earlier Debian 11 image.

What Hanwei Adds to Upstream Debian 12

• Tuning baseline applied identically across the catalogue: the file descriptor limit goes from 1024 to 65536 and the memory-map ceiling from 65530 to 262144; the device receive backlog goes from 1000 to 16384 and the TCP SYN backlog from 128 to 8192, so bursts queue instead of being dropped; socket buffer maxima reach 16 MB for larger autotuned windows; connections keep their congestion window across idle periods; and the journal is capped at 500 MB. The profile raises ceilings only and does not alter protocol semantics or application behaviour.
• Applied hardening beyond the distribution default: SSH is limited to a vetted cipher, key exchange and MAC list, X11 forwarding is off, the login grace period is shortened and verbose authentication logging is on; auditd runs a base rule set for privileged command execution; the kernel drops ICMP redirects on IPv4 and IPv6, logs martian packets, filters reverse paths in loose mode, restricts dmesg and turns off sysrq.
• AWS operational integration: the SSM Agent is installed and enabled for Session Manager and Patch Manager without an inbound SSH rule; chrony points at the Amazon Time Sync Service; and the root filesystem extends at boot when the volume exceeds the image default.
• Patch level set at the build date: packages come from official upstream repositories at the newest level published when the image was built.
• Repeatable build and EC2 validation: each version comes from the same build process and is launched and exercised on EC2 before release.

Access and Security Posture

• AppArmor is active and auditd records activity against a base rule set.
• Sign in as 'admin' with the key pair selected at launch, then use 'sudo su -' for a root shell. Session Manager is available as an alternative that needs no inbound port.
• Direct root login over SSH is disabled and password authentication is not accepted.
• No authorized keys and no SSH private keys are embedded in the image.

Operational Impact on EC2

• Launch-to-usable time is reduced to a single boot cycle, with no configuration pass.
• Every instance starts from an identical configuration, removing drift between development, staging and production hosts.
• Network services need no per-host limit or backlog adjustment before handling load.
• Clock accuracy comes from the Amazon Time Sync Service, which matters for log correlation and request signing.
• Post-launch patching effort is lower because the package set is current at release.

Where This Image Fits

• Long-lived server workloads that need apt and Debian packaging policy rather than an RPM base.
• Base image for internal golden images and infrastructure-as-code pipelines.
• Fleets managed through Systems Manager, where Session Manager access is required from first boot.
• Migration target for workloads consolidating onto Debian 12.

About Debian 12

Debian is a community-maintained Linux distribution with a long release cycle and a large package archive. Each stable release receives security support for roughly five years through the security and LTS teams, and apt provides dependency resolution and rollback across that period. Its packaging policy and conservative defaults make it a common choice for long-lived server workloads.

This image starts from the Debian 12 amd64 image published by the Debian project and adds the configuration described above. apt still points at the official Debian repositories, so security updates arrive through the normal channel. The login account is 'admin' with sudo. Debian 12 carries the 6.1 kernel series and receives security support into 2028.