Hardened CentOS Stream 9

Charges for this image cover the security hardening, optimization, and pre-integration work Hanwei performs on top of the upstream CentOS Stream 9 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. A team that would otherwise repeat a post-launch configuration pass on every instance starts from this instead.

What Hanwei Adds to Upstream CentOS Stream 9

• 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, disables setuid core dumps 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

• SELinux runs in enforcing mode and auditd records activity against a base rule set.
• Sign in as 'ec2-user' 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

• Base image for internal golden images and infrastructure-as-code pipelines that need a known starting state.
• Application hosts where the operating system baseline must be consistent across environments.
• Fleets managed through Systems Manager, where Session Manager access is required from first boot.
• Workloads that open many sockets or files and would otherwise meet the 1024 descriptor default.

About CentOS Stream 9

CentOS Stream 9 is a Linux distribution that tracks the development stream of Red Hat Enterprise Linux 9. Packages land in CentOS Stream before they appear in a RHEL minor release, so it stays close to the RHEL package set and toolchain while remaining freely redistributable. It uses dnf for package management, systemd for service supervision and SELinux for mandatory access control, which makes it a predictable base for server workloads that need RHEL compatibility.

This image starts from the CentOS Stream 9 x86_64 image published by the CentOS project. Nothing is removed: dnf still points at the official CentOS repositories, so the normal update and rollback paths continue to work, and the separate boot and EFI partitions from the upstream layout are preserved. The login account is 'ec2-user' with sudo.