Hello wandenberg,

Thank you for your response. I truly appreciate your help. I tried this options given below

######First Method###############
1. Edit nginx.conf and add
map $uri $custom_content_type {
default "text/html";
~(.*\.json)$ "application/json";
}

2. Put the custom map in location directive
location / {
proxy_redirect off;
proxy_set_header Host www-aaa.com.s3.amazonaws.com;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Referer www-aaa.com;
proxy_pass http://www-aaa.com.s3.amazonaws.com/;
add_header Pragma "no-cache";
proxy_cache_valid 200 302 10m;
proxy_read_timeout 60s;
proxy_hide_header Content-Type;
add_header Content-Type $custom_content_type;
}

######Second Method###############
1. Edit nginx.conf and add
map $uri $custom_content_type {
default "text/html";
~(.*\.json)$ "application/json";
}

2. Put the custom map in location directive
location / {
proxy_redirect off;
proxy_set_header Host www-aaa.com.s3.amazonaws.com;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Referer www-aaa.com;
proxy_pass http://www-aaa.com.s3.amazonaws.com/;
add_header Pragma "no-cache";
proxy_cache_valid 200 302 10m;
proxy_read_timeout 60s;
location ~ \.json$ {
proxy_hide_header Content-Type;
add_header Content-Type $custom_content_type;
}
}

##Third Method####################

1. Enter this in server block of nginx.
location ~ \.json$ {
types { }
default_type application/json;
}

#################################

1. When I tried first method I put below content in "location / { }" and due to this the JSON file served as application/json but all other files loaded as text/html as it was default in the map directive which caused image/css to not load. I thought it would read the mime.types files and will select the appropriate Content-Type.
#########################
proxy_hide_header Content-Type;
add_header Content-Type $custom_content_type;
##########################

2. When I tried second and third method, I am getting 404 because it is taking docroot as /var/empty

2014/08/07 17:13:22 [error] 14205#0: *33 open() "/var/empty/aaa/bbb/ccc/ddd/eee.json" failed (2: No such file or directory), client: 5.5.5.5., server: www-aaa.com, request: "GET /aaa/bbb/ccc/ddd/eee.json HTTP/1.1", host: "www.aaa.coml"

So my question is where should I put the location ~\.json block(in location / {} or in server directive)?

**************my NGINX.conf********************
user nginx;
worker_processes 1;
error_log /var/log/nginx/error.log notice;
pid /var/run/nginx.pid;
worker_rlimit_nofile 30000;
events {
worker_connections 1024;
}
http {
include /etc/nginx/mime.types;
default_type application/octet-stream;

log_format main '$remote_addr - $remote_user [$time_local] $request '
'"$status" $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';
log_format combined_time '$remote_addr - $remote_user [$time_local]'
'"$request" $status $body_bytes_sent '
'"$http_referer" "$http_user_agent" $request_time';

access_log /var/log/nginx/access.log combined_time;
include /etc/nginx/servers/*.conf;
}
**********************************************

******************************VHOST SETTING*****
server {
listen 80;
server_name www-aaa.com;
add_header Cache-Control off;
expires 1d;
root /var/empty;
error_log /var/log/nginx/www.aaa.com-error.log;
access_log /var/log/nginx/www.aaa.com-access.log combined_time;
location = /favicon.ico {
root /www;
}
proxy_intercept_errors on;
error_page 400 401 402 403 404 406 407 408 409 410 411 412 413 414 415 416 417 495 496 497 500 501 502 503 504 505 506 507 = /error_page.pl;
error_page 405 =200 $uri;
location /error_page.pl {
fastcgi_pass 127.0.0.1:8999;
fastcgi_param REQUEST_URI $request_uri;
fastcgi_pass_header "Status";
}

location / {
proxy_redirect off;
proxy_set_header Host www.aaa.com.s3.amazonaws.com;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Referer www.aaa.com;
proxy_pass http://www.aaa.com.s3.amazonaws.com/;
}
}
***************************************************************************

NOTE: All my files are served from s3 bucket and not a single files are in the server.

--Manish