Varnish Raw

*   The flowchart's really helpful in visualizing how Varnish handles a
    request before asking the backend.
*   `default.vcl` comes with commented out subroutines which are worth
    a study.
    *   I commented the hell out of them in this repo.
*   Test code with

        varnishd -C -f /etc/varnish/default.vcl


    # Install the repo  
    rpm -ivh
    # Install Varnish  
    yum -y install varnish  
    # Make copy of config  
    cp /etc/varnish/default.vcl{,.original}

Can now start a varnish daemon with `varnishd` and specify the start
params [like the documentation asks you to
But will use init daemons and sysconfig options on a RHEL box, which is

Edit `/etc/sysconfig/varnish`. Changed some default options:

    # Listen on all addresses, on the HTTP port  
    # Use a 250MB cache  
    # Use malloc  

Both "file" and "malloc" use disk and memory, [but in different

This is the plan:

    World ---> Varnish ---> Nginx ---> Application Server  

In this case, the Nginx server is considered a "backend server" from
which Varnish can request and then get data. I defined a simple one in

    # Define a simple Nginx backend
    backend nginx_server {
            .host = "localhost";
            .port = "8080";

Restarted the varnish and nginx services, made sure they were listening
on the right ports.

    [root@example conf.d]# netstat -tunlp | grep 80  
    tcp  0   0*     LISTEN   27090/varnishd  
    tcp  0   0*     LISTEN   26861/nginx

The site should now work exactly as before. A few notes:

*   There's no caching taking place. Yet. That's where the VCL
    comes in.
*   Since I only have one server, I'm not interested in Varnish's
    load-balancing capabilities.


### vcl\_recv

The entry point. I played around with the default subroutine by simply
adding this to `default.vcl` and restarting Varnish:

    sub vcl_recv {
        # Check for a standard HTTP verb. If none used, bark.
        if (req.request != "GET") {
                error 400 "I don't understand what you want me to do.";

After that, a simple `curl -X POST` yielded:

        *400 I don't understand what you want me to do.*

Error 400 I don't understand what you want me to do.

I don't understand what you want me to do.

Guru Meditation:

XID: 2033234310

Varnish cache server

Nice. ### vcl\_hash Varnish uses a key-value memory map. This subroutine defines how the key is generated. By default, it uses (URL or IP) + hostname. ### vcl\_pipe and vcl\_pass Called when `return(pipe)` or `return(pass)` are... returned from `vcl_recv`. In pipe mode is the simplest "Varnish-bypass" mode, where it short-circuits the connection between the client and the backend. No caching, no logging. Varnish does nothing while client speaks to backend (still through Varnish.) In pass mode, Varnish can look at (and manipulate) request and response data ### vcl\_fetch * A full restart wipes the cache: neither "file" nor "malloc" are persistent. * You can see how Varnish translates the VCL into C code by: `   varnishd -C -f /etc/varnish/default.vcl` * Here's a useful [list of actions](