Hi,
We are implementing an stale-while-revalidate webserver cluster with NGINX.
We are using the new proxy_cache_background_update to answer request as
soon as possible while NGINX updates the content from the origin in the
background. This solution works perfectly when the requests for the same
object are served by the same NGINX server (when we have only one server
or when we have a previous load balancer that classifies the requests).
In our scenario we have a round robin load balancer (ELB) and we need to
scale the webservers layer. So, as a consequence, only the Nginx that
receive the request updates the cache content while the others keep the
old version. This means that, we can send old versions of content due to
the content not being updated on all the webservers. The problem
accentuates when we put a CDN in front of the webservers.
We are thinking on developing something that once an Nginx instance
updates its cache would let know all other instances to get a copy of
the newest content. We are thinking about processing NGINX logs and,
when it detects a MISS, EXPIRED or UPDATING cache status, it makes a
HEAD request to the other NGINXs on the cluster to force the
invalidation of this content.
Do any of you have dealt with this problem or a similar one?
We have also tried the post_action but it is blocking the client request
until it completes. It is not clear for us which would be the best
approach. The options that we are considering are:
- NGINX module
- LUA script
- External script that process syslog entries from NGINX
What would be your recommendation?
Many thanks in advance,
--
Joan Tomàs-Buliart
www.marfeel.com <http://www.marfeel.com>
Joan Tomàs-Buliart
+34 931 785 950
www.marfeel.com <http://www.marfeel.com>
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<http://blog.marfeel.com/earn-money-marfeel-referral-program/>
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