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<div dir="ltr">> In that case, hashing the URL only would prevent you from adding new
<div>domains through your Varnish server. It won't hurt if you know you</div>
<div>will only ever have one domain to deal with, but hashing the host will</div>
<div>also not hurt as long as you normalize it to a unique value.</div>
<div><br>
</div>
<div>Hi,</div>
<div>Let me elaborate my architecture more:</div>
<div>I have some backend servers to serve hls fragments for video live stream,e.g:</div>
<div><br>
</div>
<div>```</div>
<div><br>
</div>
<div>hls_backend_01</div>
<div>hls_backend_02</div>
<div>hls_backend_03</div>
<div>hls_backend_04</div>
<div>hls_backend_05</div>
<div>hls_backend_06</div>
<div>hls_backend_07</div>
<div>hls_backend_08</div>
<div>hls_backend_09</div>
<div>hls_backend_10</div>
<div><br>
</div>
<div>```</div>
<div><br>
</div>
<div>There is same content on all hls backend servers, there are 5 varnish in front of them for caching</div>
<div>Now If I use round-robin director on Varnishes, because varnish would cache " req.http.host + req.url ", so for the same content but from different backends it would cache double! for example:</div>
<div>if varnish for the first request and "test.ts" file goes to "hls_backend_01" backend server, would cache it and</div>
<div>for the next request from other clients because it is using round-robin director</div>
<div>it goes to "hls_backend_02" and would cache the same file again due to different "req.http.host"
</div>
<div>So now I have a solution to use Shard director based on "key=req.url" instead of round robin</div>
<div>another way is to use round robin but adjusting the hash vcl to something like bellow:</div>
<div><br>
</div>
<div>```</div>
<div><br>
</div>
<div>sub vcl_hash {</div>
<div> hash_data(req.url);</div>
<div> return (lookup);</div>
<div>}</div>
<div><br>
</div>
<div>```</div>
<div><br>
</div>
<div>In this way varnish just hash the "req.url" not "req.http.host"</div>
<div>So, Varnish would cache the content based on the content uniqueness not based on the difference between backends.</div>
<div>1. At first, I asked how I can normalize it, Is it possible at all according to what I said!?</div>
<div>Would you please explain it more with an example?</div>
<div><br>
</div>
<div>2. You give an example about other domains, In this case I do not understand what it has to do with the domain?</div>
<div><br>
</div>
<div>
<div><span>3.Maybe I'm thinking in wrong way because if varnish hash the data based on req.url :
</span>'hash_data(req.url)' It shouldn't cache the same content but different backends again!</div>
<div><span>for example my request is :</span></div>
<div><span><br>
</span></div>
<div><span>http://varnish-01:/hls/test.ts</span></div>
<div><span>for first request it goes to "<span>hls_backend_01</span><span></span>" backend and cache it and for next request it goes to "<span><span>hls_backend_02</span></span>" backend,</span></div>
<div><span>so for each request it caches it again because backends are different?<br>
</span></div>
<div><span><br>
</span></div>
</div>
Many Thanks, Hamidreza </div>
</div>
</div>
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<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> varnish-misc <varnish-misc-bounces+hrhosseini=hotmail.com@varnish-cache.org> on behalf of Dridi Boukelmoune <dridi@varni.sh><br>
<b>Sent:</b> Sunday, August 15, 2021 10:30 PM<br>
<b>To:</b> varnish-misc@varnish-cache.org <varnish-misc@varnish-cache.org><br>
<b>Subject:</b> Re: Best practice for caching scenario with different backend servers but same content</font>
<div> </div>
</div>
<div class="BodyFragment"><font size="2"><span style="font-size:11pt;">
<div class="PlainText">On Sat, Aug 14, 2021 at 10:54 AM Hamidreza Hosseini<br>
<hrhosseini@hotmail.com> wrote:<br>
><br>
> Hi,<br>
> Thanks to you and all varnish team for such answers that helped me alot,<br>
> I read the default varnish cache configuration again:<br>
> <a href="https://github.com/varnishcache/varnish-cache/blob/6.0/bin/varnishd/builtin.vcl">
https://github.com/varnishcache/varnish-cache/blob/6.0/bin/varnishd/builtin.vcl</a><br>
> and find out vcl_hash as follow:<br>
><br>
> ```<br>
> sub vcl_hash {<br>
> hash_data(req.url);<br>
> if (req.http.host) {<br>
> hash_data(req.http.host);<br>
> } else {<br>
> hash_data(server.ip);<br>
> }<br>
> return (lookup);<br>
> }<br>
><br>
> ```<br>
> So, if I change vcl_hash like following , would it be enough for my purpose?(I mean caching the same object from different backends just once with roundrobin directive !:)<br>
><br>
> ```<br>
><br>
> sub vcl_hash {<br>
> hash_data(req.url);<br>
> return (lookup);<br>
> }<br>
><br>
> ```<br>
><br>
> By this config I told varnish just cache the content based on the 'req.url' not 'req.http.host' therefore with the same content but different backend varnish would cache once(If I want to use round robin directive instead of shard directive ), Is this true?
what bad consequences may it cause in the future by this configuration?<br>
<br>
In this case req.http.host usually refers to the the domain end users<br>
resolve to find your varnish server (or other hops in front of it). It<br>
is usually the same for every client, let's take <a href="http://www.myapp.com">www.myapp.com</a> as an<br>
example. If your varnish server is in front of multiple services, you<br>
should be handling the different host headers explicitly. For exampe<br>
if you have exactly two domains you should normalize them to some<br>
canonical form. Using the same example domain that could be<br>
<a href="http://www.myapp.com">www.myapp.com</a> and static.myapp.com for instance.<br>
<br>
In that case hashing the URL only would prevent you from adding new<br>
domains through your Varnish server. It won't hurt if you know you<br>
will only ever have one domain to deal with, but hashing the host will<br>
also not hurt as long as you normalize it to a unique value.<br>
<br>
You are correct that by default hashing the request appropriately will<br>
help the shard director do the right thing out of the box. I remember<br>
however that you only wanted to hash a subset of the URL for video<br>
segments, so hashing the URL as-is won't provide the behavior you are<br>
looking for.<br>
<br>
Dridi<br>
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