load-balancing

[Andrei]

On Mon, Mar 20, 2017 at 8:45 PM, Jason Price <japrice at gmail.com> wrote:

> Andrei:
>
> Why do you care that the cache is synchronized between each remote DC?
>

Because that's the whole point of having a CDN, with High Availability.
There's no reason not to keep cache consistent across the board, and have
low latency per region regardless of requests from that particular region -
aka cache priming. For example, if the origin server in North America
receives a cacheable request from a client, that data is then instantly
made available to all regions. So when client2 from Europe requests the
same page, they get consistent data without the added 100ms+ latency spike
per origin fetch. This is just good common practice for optimizing large
traffic loads and keeping data consistent - imo. Afaik, Varnish Plus
actually offers something along these lines, for a good reason -
https://www.varnish-software.com/plus/varnish-high-availability/


>
> The simple way would be to do your any-cast'd IPs be your front end, and
> have them all talk to a centralized 'private' varnish which fronts the
> actual service.
>
> This would allow the individual servers to have a more relevant to their
> queries cache, and the centralized version would handle any duplication of
> requests from making it back to the true backend.
>
>
The anycast IPs are "in front" of the Varnish boxes. However, there is no
"centralized" Varnish to handle the requests as that wouldn't be optimal
for a CDN. The closest by comparison would be the origin server, in terms
of a "centralized version". Think of this setup as a decentralized mesh
which shares data among a set group of Varnish servers for High
Availability and low latency regardless of region.


> On Sat, Mar 18, 2017 at 4:28 AM, Andrei <lagged at gmail.com> wrote:
>
>> (dubbing this over from the mod_auth thread for relevance due to my
>> mistake earlier)
>>
>> Out of curiosity, has anyone done a CDN of Varnish servers? I have 4
>> Varnish servers in different datacenters around the world, and use anycast
>> IPs to direct traffic based on the region. I managed to do cache
>> replication using a "fanout" method for new cache hits to be replicated
>> through an intermediary server to the related group of Varnish servers, but
>> was wondering if anyone had a better method of load balancing with cache
>> replication.
>>
>> On Fri, Mar 17, 2017 at 8:47 AM, Rodney Bizzell <rbizzell at measinc.com>
>> wrote:
>>
>>> Thanks!
>>>
>>>
>>>
>>> *From:* Guillaume Quintard [mailto:guillaume at varnish-software.com]
>>> *Sent:* Friday, March 17, 2017 9:34 AM
>>> *To:* Rodney Bizzell <rbizzell at measinc.com>
>>> *Cc:* varnish-misc at varnish-cache.org
>>> *Subject:* Re: load-balancing
>>>
>>>
>>>
>>> The docs have this: http://varnish-cache.org/docs/5.0/reference/vcl.html
>>> (you are interested in bereq.backend and req.backend_hint) and
>>> http://varnish-cache.org/docs/5.0/reference/vmod_directors.g
>>> enerated.html
>>>
>>>
>>>
>>> And there is a couple of articles about it:
>>>
>>> https://info.varnish-software.com/blog/backends-load-balancing
>>>
>>> https://info.varnish-software.com/blog/backends-load-balancing-part-2
>>>
>>>
>>> --
>>>
>>> Guillaume Quintard
>>>
>>>
>>>
>>> On Fri, Mar 17, 2017 at 1:48 PM, Rodney Bizzell <rbizzell at measinc.com>
>>> wrote:
>>>
>>> Hello,
>>>
>>> In the documentation is there a section on setting-up load-balancing
>>> between two varnish servers.
>>>
>>>
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>>
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