NGINX stale-while-revalidate cluster
peter_booth at me.com
Sat Jul 8 13:30:15 UTC 2017
Perhaps it would help if, rather than focus on the specific solution that you are wanting, you instead explained your specific problem and business context?
What is driving your architecture? Is it about protecting a backend that doesn't scale or more about reducing latencies?
How many different requests are there that might be cached? What are the backend calls doing? How do cached objects expire? How long does a call to the backend take?
Why is it OK to return a stale version of X to the first client but not OK to return a stale version to a second requester?
Imagine a scenario where two identical requests arrive from different clients and hit different web servers. Is it OK for both requests to be satisfied with a stale resource?
It's very easy for us to make incorrect assumptions about all of these questions because of our own experiences.
Sent from my iPhone
> On Jul 8, 2017, at 9:00 AM, Joan Tomàs i Buliart <joan.tomas at marfeel.com> wrote:
> Thanks Owen!
> We considered all the options on these 2 documents but, on our environment in which is important to use stale-while-revalidate, all of them have, at least, one of these drawbacks: or it adds a layer in the fast path to the content or it can't guarantee that one request on a stale content will force the invalidation off all the copies of this object.
> That is the reason for which we are looking for a "background" alternative to update the content.
> Many thanks in any case,
>> On 07/07/17 16:04, Owen Garrett wrote:
>> There are a couple of options described here that you could consider if you want to share your cache between NGINX instances:
>> https://www.nginx.com/blog/shared-caches-nginx-plus-cache-clusters-part-1/ describes a sharded cache approach, where you load-balance by URI across the NGINX cache servers. You can combine your front-end load balancers and back-end caches onto one tier to reduce your footprint if you wish
>> https://www.nginx.com/blog/shared-caches-nginx-plus-cache-clusters-part-2/ describes an alternative HA (shared) approach that replicates the cache so that there’s no increased load on the origin server if one cache server fails.
>> It’s not possible to share a cache across instances by using a shared filesystem (e.g. nfs).
>> owen at nginx.com
>> Skype: owen.garrett
>> Cell: +44 7764 344779
>>> On 7 Jul 2017, at 14:39, Peter Booth <peter_booth at me.com> wrote:
>>> You could do that but it would be bad. Nginx' great performance is based on serving files from a local Fisk and the behavior of a Linux page cache. If you serve from a shared (nfs) filsystem then every request is slower. You shouldn't slow down the common case just to increase cache hit rate.
>>> Sent from my iPhone
>>> On Jul 7, 2017, at 9:24 AM, Frank Dias <frank.dias at prodea.com> wrote:
>>>> Have you thought about using a shared file system for the cache. This way all the nginx 's are looking at the same cached content.
>>>> On Jul 7, 2017 5:30 AM, Joan Tomàs i Buliart <joan.tomas at marfeel.com> wrote:
>>>> Hi Lucas
>>>> On 07/07/17 12:12, Lucas Rolff wrote:
>>>> > Instead of doing round robin load balancing why not do a URI based
>>>> > load balancing? Then you ensure your cached file is only present on a
>>>> > single machine behind the load balancer.
>>>> Yes, we considered this option but it forces us to deploy and maintain
>>>> another layer (LB+NG+AppServer). All cloud providers have round robin
>>>> load balancers out-of-the-box but no one provides URI based load
>>>> balancer. Moreover, in our scenario, our webservers layer is quite
>>>> dynamic due to scaling up/down.
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