I'm not sure how "hash $cachekey" works...

[highclass99]

Thank you for your reply.

You replied:
> With Config1 and Config2 you have 160 hash points per each server
(duplicates are removed)

Does that mean
I could just shorten the whole config to
 upstream ImageCluster  {
   server 10.1.1.1;
   server 10.1.1.2;
   server 10.1.1.3;
   hash $cachekey consistent;
 }
and it would be exactly the same and keep the hashes exactly the same as
before?

If I wanted to "weight" the servers to all initially weight=4 and then
slowly optimize the weightings.
Would it be a good idea to slowly add the weightings as
weight=2 -restart and wait-> weight=3 -restart and wait-> weight=4
(the servers have really high load, and sudden changes in hash can cause
problems)
or would it be okay to just change at once like
 upstream ImageCluster  {
   server 10.1.1.1 weight=4;
   server 10.1.1.2 weight=4;
   server 10.1.1.3 weight=4;

   hash $cachekey consistent;
 }

Again, thanks for your reply.


On Fri, Jan 22, 2016 at 1:05 AM, Roman Arutyunyan <arut at nginx.com> wrote:

> Hi,
>
> > On 21 Jan 2016, at 15:41, highclass99 <highclass99 at gmail.com> wrote:
> >
> > I have a question about "hash $cachekey" consistent;
> > Would the following Config 1, Config 2, Config 3 be exactly the same of
> different?
> > i.e. if I swap the configurations would the cache keys stay consistent?
> > The reason I am asking is I have a large configuration similar to Config
> 2 and am not sure it would be "safe" to clean up the order and merge
> duplicates as weighted config values.
> >
> > Thank you.
> >
> > Would the following be different of the same?
> > Config 1:
> > upstream ImageCluster  {
> >   server 10.1.1.1;
> >   server 10.1.1.1;
> >   server 10.1.1.2;
> >   server 10.1.1.2;
> >   server 10.1.1.3;
> >   server 10.1.1.3;
> >
> >   hash $cachekey consistent;
> > }
> >
> > Config 2:
> > upstream ImageCluster  {
> >   server 10.1.1.2;
> >   server 10.1.1.2;
> >   server 10.1.1.1;
> >   server 10.1.1.1;
> >   server 10.1.1.3;
> >   server 10.1.1.3;
> >
> >   hash $cachekey consistent;
> > }
>
> These two are the same.  With consistent hash balancer the order of servers
> does not matter.
>
> > Config 3:
> > upstream ImageCluster  {
> >   server 10.1.1.1 weight=2;
> >   server 10.1.1.2 weight=2;
> >   server 10.1.1.3 weight=2;
> >
> >   hash $cachekey consistent;
> > }
>
> This one is different.
>
> With Config1 and Config2 you have 160 hash points per each server
> (duplicates are removed).
> With Config3 you have 320 points per each server.
>
> Statistically all configurations are similar.
>
> --
> Roman Arutyunyan
>
>
>
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