NGINX and Varnish Connection failed (localhost:6082)

My wordpress site gives error 521 all the times.

When I found this error from my server

$sudo service varnish reload
 * Reloading HTTP accelerator varnishd                                                                                                     Connection failed (localhost:6082)
Error: vcl.load 8d6fb6be-9a0a-4896-be47-e2678e3c2617 /etc/varnish/default.vcl failed

Moreover, varnishlog shows nothing.

I am following this tutorial to set the server up. And, I changed

DAEMON_OPTS="-a :80 \
    -T localhost:6082 \
    -f /etc/varnish/default.vcl \
    -u www-data -g www-data \
    -S /etc/varnish/secret \
    -s malloc,256m"

The /etc/varnish/default.vcl file is copied from the tutorial. All &a mp; has been corrected to &.

It is a fresh droplet. No firewall.

Any clue to resolve it?

Thanks!!!