I have requirement where proxy handler needs to talk to multiple server before sending request to actual server where it gets processed. For example proxy handler receives user request, talks to virus scanner to see user data contain any virus or not then only forward to actual server. Here virus scanner may be another server or a thread part of nginx. My doubts are

1) When I went through proxy module, ngx_http_proxy_create_request is the callback responsible to prepare request to send to another server. As per understanding, I need to call here virus scanner before sending request. Is it correct? Or is there any other place I can do this work? In this function if I call virus scanner API's, how will the request forwarded the server which serves request?

2) How to make it asynchronous with out effecting nginx's performance.

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Thanks