Tune Varnish Cache on Debian 12

Systemd override (/etc/systemd/system/varnish.service.d/override.conf)

[Service]
ExecStart=
ExecStart=/usr/sbin/varnishd \
    -a :80 -T localhost:6082 \
    -f /etc/varnish/default.vcl \
    -s malloc,2G \
    -p thread_pools=2 \
    -p thread_pool_min=200 \
    -p thread_pool_max=4000 \
    -p thread_pool_timeout=300

Key parameters

Monitor hit rate

varnishstat -1 | grep -E 'MAIN\.(cache_hit|cache_miss)'

Live request log

varnishlog -i ReqURL -i RespStatus
varnishlog -q "VCL_call eq MISS" -i ReqURL