linuxexpert-practice-labs/labs/lfca/3-2-performance-availability/README.md

LFCA 3.2: Performance and availability

The downtime each number of nines allows, and nginx as a load balancer in front of two web servers.

Before you start

Work as root (sudo -i). Answers go in /root/lab-answers/<task>.

The peer, at 10.99.0.2 (name peer), stands in for the two web server VMs: it runs one web server on port 8081 and another on port 8082, each with its own home page (le-lab-backend1.service and le-lab-backend2.service on this VM). This VM is the load balancer. The lab notes whether nginx is installed, and reset puts that back. The VM needs internet access to install nginx.

Tasks

1. Work out the yearly downtime allowed by 99.9%, 99.95% and 99.99%, in minutes, and check them against the chapter's table. Write them to /root/lab-answers/1, one per line, in that order.
2. Install nginx on this VM and make it a load balancer on port 80: an upstream block with zone backend 64k; and the two servers (10.99.0.2:8081 and 10.99.0.2:8082), and proxy_pass. Run for i in 1 2 3 4 5 6; do curl -s http://localhost/; done and watch the answers alternate. Leave nginx running and starting at boot.
3. Stop one web server (systemctl stop le-lab-backend2) and watch the traffic move to the other. Start it again afterwards. Not graded.

Hints

• A year has 365 × 24 × 60 = 525,600 minutes; 99.9% allows 0.1% of that.
• A file in /etc/nginx/conf.d/ with upstream backend { ... } and a server { listen 80; location / { proxy_pass http://backend; } }. nginx -t, systemctl enable --now nginx, systemctl reload nginx.
• Only one server block can answer for port 80 by default. On Ubuntu, remove the default link in /etc/nginx/sites-enabled/.
• A 502 Bad Gateway on the RHEL family with SELinux enforcing: nginx may not connect out until you allow it with setsebool -P httpd_can_network_connect on.