How to install Varnish with Docker /
Spin up a varnish server for testing

26/03/2024

In this brief blog post, I'll show you an easy way to set up a Docker container with Varnish to test how Varnish behaves with VCL (Varnish Configuration Language). This method is fast, simple, and can be really useful for testing or debugging your VCL code.

Create the docker container


docker run --name varnish -p 3456:80 varnish

This command runs a Docker container named « varnish » using the « varnish » image. It maps port 3456 on the host to port 80 in the container, allowing access to the containerized varnish service.

Start the container


docker start varnish

Find your local ip address


ifconfig | grep 192

Returns :

inet 192.168.1.105 netmask 0xffffff00 broadcast 192.168.1.255
inet 192.168.64.1 netmask 0xffffff00 broadcast 192.168.64.255

Here is the ip I will use as hostname : 192.168.1.105

Create a default VCL

On my local machine I created : default.vcl


vcl 4.0; backend default { .host = "192.168.64.1"; .port = "3455"; }

The host and the port are the one from my application behind Varnish

Copy the VCL in the container

docker cp default.vcl varnish:/etc/varnish

Restart the container

docker restart varnish

Start to play with the VCL

vcl 4.0;

backend default {
  .host = "192.168.64.1";
  .port = "3455";
}




sub vcl_recv {

    if (req.url ~ "keep-fresh") {
        return (pass);
    }

}



sub vcl_backend_response {

    # Set a default
    set beresp.ttl = 30s;

    if(bereq.url ~ "data"){
        set beresp.ttl = 8s;
    }

}
sub vcl_deliver {

    set resp.http.Antoine = "Hello";
}

Copy the custom VCL and restart in one command

docker cp default.vcl varnish:/etc/varnish && docker restart varnish

Do not cache a specific url :

sub vcl_recv {

    if (req.url ~ "keep-fresh") {
        return (pass);
    }

}

When I call http://localhost:3456/keep-fresh it’s never cached :

abrossault@macbook ~ % curlHeaders http://localhost:3456/keep-fresh
HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: application/json; charset=utf-8
Content-Length: 35
ETag: W/"23-gZVVGSUOoG7U6R/CPEAL+l/wRng"
Date: Tue, 26 Mar 2024 13:16:17 GMT
X-Varnish: 492
Age: 0
Via: 1.1 5f6b48482a6f (Varnish/7.5)
Antoine: Hello
Connection: keep-alive

Only cache an url for 8sec

sub vcl_backend_response {

    # Set a default
    set beresp.ttl = 30s;

    if(bereq.url ~ "data"){
        set beresp.ttl = 8s;
    }

}

When I call http://localhost:3456/data it will remain in cache for only 8sec

abrossault@macbook ~ % curlHeaders http://localhost:3456/data
HTTP/1.1 200 OK
X-Powered-By: Express
ETag: W/"5fc7-3rbdk4/NvVpLo6VEDXT1gH26XH8"
Date: Tue, 26 Mar 2024 13:18:44 GMT
Content-Type: application/json; charset=utf-8
Content-Length: 24519
X-Varnish: 98308 32836
Age: 8
Via: 1.1 5f6b48482a6f (Varnish/7.5)
Accept-Ranges: bytes
Antoine: Hello
Connection: keep-alive

Here the Age is 8 Age: 8

Then when I call this URL again the Age header is reset :

abrossault@macbook ~ % curlHeaders http://localhost:3456/data
HTTP/1.1 200 OK
X-Powered-By: Express
ETag: W/"5fc7-3rbdk4/NvVpLo6VEDXT1gH26XH8"
Date: Tue, 26 Mar 2024 13:18:53 GMT
Content-Type: application/json; charset=utf-8
Content-Length: 24519
X-Varnish: 505 98309
Age: 2
Via: 1.1 5f6b48482a6f (Varnish/7.5)
Accept-Ranges: bytes
Antoine: Hello
Connection: keep-alive

Cache static assets for 7 days

All the assets finish with (css|js|png|jpg|jpeg|gif|ico|woff|woff2|svg|otf|ttf|eot) will be cached for 7 days, and we put a cache-control header

sub vcl_backend_response {

    # Set a default
    set beresp.ttl = 30s;

    if (bereq.url ~ "\.(css|js|png|jpg|jpeg|gif|ico|woff|woff2|svg|otf|ttf|eot)$") {
        set beresp.ttl = 7d; // Cache static assets for 7 days
        set beresp.http.Cache-Control = "public, max-age=604800"; // Set cache-control header
    } 

}

As you can see after few minutes my Age header went up by more than the default ttl

abrossault@macbook ~ % curlHeaders http://localhost:3456/js/app.js
HTTP/1.1 200 OK
X-Powered-By: Express
Last-Modified: Tue, 26 Mar 2024 13:39:12 GMT
ETag: W/"15-18e7afc80c4"
Content-Type: application/javascript; charset=UTF-8
Content-Length: 21
Date: Tue, 26 Mar 2024 13:55:58 GMT
Cache-Control: public, max-age=604800
X-Varnish: 77 32771
Age: 669
Via: 1.1 5f6b48482a6f (Varnish/7.5)
Accept-Ranges: bytes
Antoine: Hello
Connection: keep-alive

Redirect a URL

sub vcl_recv {

    if (req.url == "/old-url") {
        return (synth(301, "/new-url")); // Redirect to new URL
    }

}

And

sub vcl_synth {
    if (resp.status == 301) {
        set resp.http.location = resp.reason;
        set resp.reason = "Moved";
        return (deliver);
    }
}

Result :

abrossault@macbook ~ % curlHeaders http://localhost:3456/old-url
HTTP/1.1 301 Moved
Date: Tue, 26 Mar 2024 14:42:28 GMT
Server: Varnish
X-Varnish: 32773
location: /new-url
Content-Length: 0
Connection: keep-alive

HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: application/json; charset=utf-8
Content-Length: 24
ETag: W/"18-/cE9SPz52ciEALTCHs8hXDUSICk"
Date: Tue, 26 Mar 2024 14:42:28 GMT
X-Varnish: 32774
Age: 0
Via: 1.1 5f6b48482a6f (Varnish/7.5)
Accept-Ranges: bytes
Antoine: Hello
Connection: keep-alive

Purge

If I want to purge a specific URL :

First set an acl with the authorized Ips


acl purge { "localhost"; "192.168.1.105"; "192.168.65.1"; } sub vcl_recv { # Purge if (req.method == "PURGE") { if (client.ip !~ purge) { return (synth(405, "Method Not Allowed for : "+client.ip)); } return (purge); } }

Then use this curl command to purge

curl  -X PURGE http://192.168.64.1:3456/data -i

Which will return :

HTTP/1.1 200 Purged
Date: Tue, 26 Mar 2024 16:03:53 GMT
Server: Varnish
X-Varnish: 32773
Content-Type: text/html; charset=utf-8
Retry-After: 5
Content-Length: 240
Connection: keep-alive

<!DOCTYPE html>
<html>
  <head>
    <title>200 Purged</title>
  </head>
  <body>
    <h1>Error 200 Purged</h1>
    <p>Purged</p>
    <h3>Guru Meditation:</h3>
    <p>XID: 32773</p>
    <hr>
    <p>Varnish cache server</p>
  </body>
</html>