I don't think it is necessary to explain what a Varnish Cache is and how it affects the load speed of the site. At least not in this post. If you are here, I suppose that you want to know how to setup SSL in Varnish.

In fact, the developer of Varnish finds it a bad idea to implement SSL support. But there are still several ways to tackle this issue.

Option 1

First, you need to understand whether it is possible to handle SSL with another service and leave communication with the server on which Varnish is installed at the default port.

Example: DigitalOcean offers Fully Managed SSL Certificates. In other words, you can create a Load Balancer and configure SSL.

Then, create a droplet on the internal network (without access from the outside), raise the environment (Varnish and other software), and attach it to the Load Balancer.

But before you start, I want to highlight that you should make sure that your hosting provider offers some solutions (Cloud Flare, etc).

Option 2

Let's imagine that we have to raise the environment to implement the API (monolith) on Laravel Framework, and we have our own VPS with root access.

The process looks like this:

Nginx handles the 443 port, handles static assets and proxy other requests to another Varnish Cache:6081.
Varnish checks the cache, and if not then proxy request to the backend (Nginx: 81, why Nginx and not PHP I will write below), gets the result, caches, and gives Nginx.
Nginx: 81 handle requests and run PHP on 9000 port or a socket.
PHP launches Laravel... It's no longer interesting to us, we've known it for a long time.

So the scheme in short:

Nninx: 443 -> Varnish: 6081 -> Nginx: 81 -> PHP: 9000

Why doesn't Varnish apply directly to PHP? Because PHP-FPM does not understand Varnish requests, and you will most likely get a 503 error.

Laravel, by the way, is a good solution since they “play nice together.”

I will skip boring guides on installing LEMP and concentrate your attention on configs.

Virtualhost for Nginx: /etc/nginx/conf.d/api.myserver.com.conf

server {

    listen 443;

    server_name www.api.myserver.com api.myserver.com;
    
    access_log   /var/log/nginx/access.log;
    error_log    /var/log/nginx/error.log;

    location = /favicon.ico { access_log off; log_not_found off; }
    location = /robots.txt  { access_log off; log_not_found off; }

    location / {
        proxy_pass http://127.0.0.1:6081;
        proxy_set_header Host $http_host;
        proxy_set_header X-Forwarded-Host $http_host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
        proxy_set_header HTTPS "on";
    }

   location ~ /\.ht {
       deny all;
   }

   location ~ /.well-known {
       allow all;
   }

    # I used letsencrypt service )

    ssl_certificate /etc/letsencrypt/live/myserver.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/myserver.com/privkey.pem;
    include /etc/letsencrypt/options-ssl-nginx.conf;
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;
}

server {

    listen 80;

    server_name  www.api.myserver.com api.myserver.com;

    return 301 https://www.$host$request_uri;

}

server {

    listen 81;

    server_name api.myserver.com www.api.myserver.com;

    root /var/www/api/public;

    index index.php;

    access_log   /var/log/nginx/access.log;
    error_log    /var/log/nginx/error.log;

    location / {
        try_files $uri $uri/ /index.php?$args;
    }

    location ~ .php$ {
	    include snippets/fastcgi-php.conf;
        fastcgi_param HTTPS on;
        fastcgi_pass   127.0.0.1:9000; # OR unix:/var/run/php7.4-fpm.sock;
    }
}

I used this template. You just have to modify the backend port.

# /etc/varnish/default.vcl
...

backend server1 { # Define one backend
  .host = "127.0.0.1";    # IP or Hostname of backend
  .port = "81";           # Port Nginx or whatever is listening
  .max_connections = 300; # That's it

...

/etc/default/varnish

...

DAEMON_OPTS="-a :6081 \ # input
             -T localhost:6082 \ # admin
             -f /etc/varnish/default.vcl \ # proxy conf
             -S /etc/varnish/secret \ # secret conf
             -s malloc,256m" 

...

That's all. Those simple maneuvers can significantly accelerate a project. I hope this little guide will help you save your time and reduce your suffering.