nginx conditional proxy pass based on request body content

Question

I am trying to configure nginx to proxy pass the request to another server, only if the $request_body variable matches on a specific regular expression.But it is not working for me.

 server{
        listen 80 default;
        server_name www.applozic.com;

        location / {
                 proxy_set_header X-Real-IP $remote_addr;
                 proxy_set_header X-Forwarded-For $remote_addr;
                 proxy_set_header Host $http_host;

                if ($request_body ~* (.*)appId(.*)) {
                   proxy_pass http://apps.applozic.com;
                }
        }

}

request body is::

              {
               "applicationId": "appId",
               "authenticationTypeId": 1,
               "enableEncryption": false,
               "notificationMode": 0,
               "deviceType": 4,
              }

Answer 1

I found the solution.

I did following changes in nginx(open resty) config file

upstream algoapp {
   server 127.0.0.0.1:543;
}
upstream main {
   server 127.0.0.1:443;
}

location /rest/ws/login {
   proxy_set_header X-Forwarded-Host $host;
   proxy_set_header X-Forwarded-Server $host;
   proxy_set_header X-Real-IP $remote_addr;
   proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
   proxy_set_header X-Url-Scheme $scheme;
   proxy_set_header X-Forwarded-Proto $scheme;
   proxy_set_header Host $http_host;
   proxy_redirect off;
   if ($request_method = OPTIONS ) {
   proxy_pass https://127.0.0.1:543;
   }
   if ($request_method = POST ) {
   set $upstream '';
   access_by_lua '
   ngx.req.read_body()
   local data = ngx.req.get_body_data()
   local  match = ngx.re.match(ngx.var.request_body, "appId")
   if match then
      ngx.var.upstream = "algoapp"
   else
   ngx.var.upstream = "main"
   end
   ';
   proxy_pass https://$upstream;
   }
}

Answer 2

As best I can tell the issue is that the variable $request_body may not have been read into memory at the time your if statement is executing.

Suggested alternatives would be to use the lua support or compile nginx with the echo modules and run echo_request_body.