Start Varnish with a config file - varnish

Question

Ubuntu 18.04.4 LTS
varnishd -V
varnishd (varnish-6.4.0 revision 13f137934ec1cf14af66baf7896311115ee35598)
Copyright (c) 2006 Verdens Gang AS
Copyright (c) 2006-2020 Varnish Software AS
My very first steps with studying Varnish and I've bitten the dust.
I've prepared a configuration file at /etc/systemd/system/varnish.service
I'm trying to start varnishd with this config:
[Unit]
Description=Varnish HTTP accelerator
Documentation=https://www.varnish-cache.org/docs/4.1/ man:varnishd
[Service]
Type=simple
LimitNOFILE=131072
LimitMEMLOCK=82000
ExecStart=/usr/sbin/varnishd -j unix,user=vcache -F -a :6081 -b :8000 -T localh$
ExecReload=/usr/share/varnish/varnishreload
ProtectSystem=full
ProtectHome=true
PrivateTmp=true
PrivateDevices=true
[Install]
WantedBy=multi-user.target
The content of the file is taken from the book "Getting started with Varnish Cache", but it is for version 4.1.
Documentation: https://varnish-cache.org/docs/6.4/users-guide/run_security.html#cli-interface-authentication
Well, I've prepared the file. I enter the command:
varnishd -S /etc/systemd/system/varnish.service
Error: Neither -b nor -f given. (use -f '' to override)
(-? gives usage)
But this command works fine:
sudo varnishd -a localhost:6081 -b localhost:8000
Could you help me understand:
What a simplest config file shoud be like.
Where it should be placed.
How to start Varnish with this config.

Answer 1

I'm the author of Getting started with Varnish Cache. Thanks for buying my book.
The varnish.service file is a systemd file. It has nothing to do with Varnish itself, but it's what Ubuntu uses to manage the Varnish service.
The ExecStart command
Here how I would set the ExecStart command in varnish.service:
/usr/sbin/varnishd -f /etc/varnish/default.vcl -a http=:80,HTTP -a proxy=:8443,PROXY -s malloc,1G -S /etc/varnish/secret -T localhost:6082
What you're not seeing in this command:
-F: the -F flag only makes sense if you're running the varnishd process in the foreground. For example in Docker. Since you'r using systemd to run Varnish, you can remove that parameter
-b: the -b option is used to define your backend location. If you use -b, you can't use -f, and you'll need -f for your VCL configuration.
What the options mean
-f: the location of the VCL file. Refers to /etc/varnish/default.vcl in this case
-a: the listening address of Varnish. In this case it's port 80 for regular HTTP and port 8443 for connections using the PROXY protocol
-s: the size of the cache, in this case 1GB
-S: the location of the secret key file. In this case this is /etc/varnish/secret
-T: the listening address of the CLI. In this case this is localhost on port 6082
The VCL file
The VCL file that contains the location of the backend and defines the caching rules. This file is located in /etc/varnish/default.vcl.
This is the minimum amount of VCL code to get going:
vcl 4.0;
backend default {
.host = "localhost";
.port = 8080;
}
This config assumes your webserver is running on the same machine, on port 8080.
You can extend the configuration of varnish by hooking into the different process states of the Varnish Finite State Machine.
See https://varnish-cache.org/docs/6.0/reference/vcl.html#varnish-configuration-language to learn more about VCL.
Activating the changes
Whenever you update varnish.service, you need to reload systemd. This is command you need:
sudo systemctl daemon-reload
To activate changes in your VCL file, you need to run the following command:
sudo systemctl reload varnish.service
Good luck!

Answer 2

Take a look here: https://varnish-cache.org/docs/6.4/users-guide/command-line.html
More detailed here: https://varnish-cache.org/docs/6.4/reference/varnishd.html
A Varnish config could for example be placed here: /etc/varnish/default.vcl
Most simple VCL:
backend default {
.host = "localhost:81";
}
How to write VCL: https://varnish-cache.org/docs/6.4/users-guide/vcl.html