LFCE case studies
LFCE · Put your knowledge to work in context.
The Linux Foundation Certified Engineer (LFCE) was an advanced, performance-based certification from the Linux Foundation, positioned above the entry-level LFCS and aimed at engineers who already administered Linux systems daily and wanted to prove depth in networking, storage, services, security, and automation. It was designed for working system administrators, DevOps and site reliability practitioners, and support engineers moving beyond single-host administration toward multi-service, multi-host environments. The LFCE case studies are 5 cases and about 3,310 words.
1Containing a runaway ingest service without losing evidence
On a 48-core, 256 GB RHEL 9 host, ingest.service processes market data and spawns up to 64 worker processes. Twice this week the host became sluggish; dmesg showed the kernel OOM killer terminating sshd and chronyd instead of ingest, and journalctl -u ingest contains only the first 90 seconds of each incident.
687 words, about 3 min2Source-based ISP selection for a vendor API client
An Ubuntu 22.04 gateway has ens3 198.51.100.10/24 (ISP A) and ens4 203.0.113.20/24 (ISP B). LAN 10.20.0.0/24 uses the gateway.
660 words, about 3 min3Thin pool exhaustion with a rollback snapshot
An Ubuntu 22.04 PostgreSQL host uses LVM thin provisioning. VG vgdata contains a 3.6 TB thin pool thinpool and two thin volumes: pgdata 2.8 TB formatted XFS and mounted at /var/lib/pgsql, and pgsnap 1.1 TB, a snapshot taken before a migration.
616 words, about 3 min4Nginx behind SELinux and firewalld on a nonstandard port
On a RHEL 9 host with SELinux enforcing, nginx 1.20 reverse-proxies an internal API at 127.0.0.1:8080 and listens on 8443 with a certificate under /etc/pki/app/tls. curl -k https://127.0.0.1:8443/health returns 200, but remote clients time out.
640 words, about 3 min5Safe Ansible rollout with apt lock contention and load balancer draining
An Ansible control node manages 200 Ubuntu 22.04 web hosts. The playbook deploy.yml uses serial: 20, a template task for /etc/nginx/conf.d/app.conf, a systemd task that restarts nginx, and a handler.
707 words, about 4 min