SNMP: add shared extension systemd units

Author: Torstein-Eide

snmp/common/README.md

@@ -0,0 +1,47 @@
+# LibreNMS SNMP Extension Common Units
+
+This directory contains shared systemd units for LibreNMS SNMP extensions that refresh cached output on a schedule.
+
+## Files
+
+- `librenms-snmp-extension@.service`: common oneshot service template.
+- `librenms-snmp-extension@.timer`: common timer template that runs an extension every five minutes.
+
+## Defaults
+
+The common service runs extension instances by name:
+
+```ini
+ExecStart=/usr/local/lib/snmpd/%i --config /etc/snmp/extension/%i.yaml --output /run/snmp/extension/%i.json
+```
+
+For an extension named `example`, this resolves to:
+
+- Script: `/usr/local/lib/snmpd/example`
+- Config: `/etc/snmp/extension/example.yaml`
+- Output: `/run/snmp/extension/example.json`
+
+Extensions that need different arguments should install a systemd drop-in override for their specific instance.
+
+The units include `Documentation=` metadata for the shared common units and the extension-specific directory. The service also sets `SyslogIdentifier=librenms-snmp-extension-%i` so logs can be filtered per extension instance.
+
+## Enable An Extension
+
+Install the shared units to `/etc/systemd/system/`, then enable the timer for the extension instance:
+
+```bash
+sudo systemctl daemon-reload
+sudo systemctl enable --now librenms-snmp-extension@example.timer
+```
+
+Check timer status:
+
+```bash
+systemctl status librenms-snmp-extension@example.timer
+```
+
+Run a refresh manually:
+
+```bash
+sudo systemctl start librenms-snmp-extension@example.service
+```

snmp/common/librenms-snmp-extension@.service

@@ -0,0 +1,17 @@
+# SNMP common extension cache.
+[Unit]
+Description=LibreNMS SNMP extension cache: %i
+Documentation=https://github.com/librenms/librenms-agent/tree/master/snmp/common
+Documentation=https://github.com/librenms/librenms-agent/tree/master/snmp/%i
+
+[Service]
+Type=oneshot
+SyslogIdentifier=librenms-snmp-extension-%i
+RuntimeDirectory=snmp/extension
+RuntimeDirectoryMode=0755
+ExecStart=/usr/local/lib/snmpd/%i --config /etc/snmp/extension/%i.yaml --output /run/snmp/extension/%i.json
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectHome=true
+ProtectSystem=full
+ReadWritePaths=/run/snmp/extension

snmp/common/librenms-snmp-extension@.timer

@@ -0,0 +1,14 @@
+# SNMP common extension cache.
+[Unit]
+Description=Run LibreNMS SNMP extension cache refresh: %i
+Documentation=https://github.com/librenms/librenms-agent/tree/master/snmp/common
+Documentation=https://github.com/librenms/librenms-agent/tree/master/snmp/%i
+
+[Timer]
+OnBootSec=2min
+OnUnitActiveSec=5min
+AccuracySec=30s
+Persistent=true
+
+[Install]
+WantedBy=timers.target