positioning of nginx

[ZHOU Xiaobo]

We can deploy a web system like below:

1)   HAProxy <---->[optinal Varnish] <----->nginx+uWSGI(communicate locally)
2)   nginx <------> uWSGI(or cluster)

as nginx can 'cache' and 'proxy',  the positioning of nginx is confusing me.

my questions are:
1, is it wrong to that nginx talks to uWSGI locally?
2, is it proper of using nginx to take over haproxy+varnish?

thx

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Sincerely yours
                         ZHOU Xiaobo