Varnish is more faster when working directory is in tmpfs. And 7.6 started nagging if not.

setup_varnish_tmpfs.sh

#!/bin/bash

# Varnish working directory location in tmpfs
TMPFS_DIR="/dev/shm/varnish"

echo "Creating directory: $TMPFS_DIR"
mkdir -p "$TMPFS_DIR"
chown -R varnish:varnish "$TMPFS_DIR"

# Path to override.conf
OVERRIDE_DIR="/etc/systemd/system/varnish.service.d"
OVERRIDE_FILE="$OVERRIDE_DIR/override.conf"

## Heads up! Change this to match your setup
echo "Writing systemd override: $OVERRIDE_FILE"
mkdir -p "$OVERRIDE_DIR"
cat > "$OVERRIDE_FILE" <<EOF
[Service]
ExecStart=
ExecStart=/usr/sbin/varnishd \\
 -I /etc/varnish/start.cli \\
 -P /var/run/varnish.pid \\
 -j unix,user=vcache \\
 -F \\
 -a :8080 \\
 -T localhost:6082 \\
 -f "" \\
 -S /etc/varnish/secret \\
 -p vsl_mask=+Hash \\
 -n $TMPFS_DIR \\
 -s malloc,5G
EOF

echo "Reloading systemd"
systemctl daemon-reexec
systemctl daemon-reload

echo "Restarting Varnish"
systemctl restart varnish

echo "Ready! Working directory is now in tmpfs: $TMPFS_DIR"