linuxexpert-practice-labs/labs/linux-plus/5-1-1-monitoring/README.md

Linux+ 5.1.1: Monitoring

An SNMP agent queried from another machine, and a health check with a threshold that logs when it fails.

Before you start

The peer, at 10.99.0.2 (name peer), stands in for the Ubuntu VM: query this VM, 10.99.0.1, from there. Get a shell there with sudo ip netns exec lepeer bash; it shares this VM's programs, so install the SNMP client tools on this VM. The lab runs a small web service on 127.0.0.1:8080, and makes the journal persistent if it isn't.

Tasks

1. Install and run an SNMP agent on this VM, enabled at boot, with a read-only community labro for the network 10.99.0.0/24, reachable from the peer. Open the firewall for it if one is running. From the peer, walk 1.3.6.1.2.1.1 and get the uptime 1.3.6.1.2.1.1.3.0.
2. Write the chapter's health-check script as health.sh in your home directory: three tries, OK with exit 0 if all succeed, WARNING with exit 1 if some fail, and if all three fail, a user.crit log message health: URL failing (CODE), CRITICAL and exit 2. Run it against http://127.0.0.1:8080/ (OK) and http://127.0.0.1:9/ (CRITICAL), and find the critical message in the journal.

Hints

• RHEL family: net-snmp, net-snmp-utils, /etc/snmp/snmpd.conf. Ubuntu: snmpd, snmp; its snmpd.conf listens on localhost only (agentaddress). rocommunity COMMUNITY SOURCE.
• firewall-cmd --add-service=snmp (and --permanent), ufw allow.
• snmpwalk -v2c -c labro 10.99.0.1 1.3.6.1.2.1.1, snmpget.
• curl -s -o /dev/null -w '%{http_code}' --max-time 3, logger -p user.crit, journalctl -p crit --since "5 min ago".