load balancer on nginx : how to monitoring backend ?

[Alexandre]

Hello everyone,

I use nginx 1.8.0 on debian (official nginx package with nginx repo)

I created a reverse proxy SSL cluster with load balancing. Everything 
works fine.

---
upstream myapp {
         server srv1;
         server srv2;
     }
---

---
location ~ ^/myapp {
         rewrite ^/(.*) /$1 break;
         proxy_pass http://myapp;
     }
---

However I wish to monitor the status of the backend. How can I do ?

Thank you.

compiler option
---
built by gcc 4.9.2 (Debian 4.9.2-10)
built with OpenSSL 1.0.1k 8 Jan 2015
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx 
--conf-path=/etc/nginx/nginx.conf 
--error-log-path=/var/log/nginx/error.log 
--http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx.pid 
--lock-path=/var/run/nginx.lock 
--http-client-body-temp-path=/var/cache/nginx/client_temp 
--http-proxy-temp-path=/var/cache/nginx/proxy_temp 
--http-fastcgi-temp-path=/var/cache/nginx/fastcgi_temp 
--http-uwsgi-temp-path=/var/cache/nginx/uwsgi_temp 
--http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx 
--group=nginx --with-http_ssl_module --with-http_realip_module 
--with-http_addition_module --with-http_sub_module 
--with-http_dav_module --with-http_flv_module --with-http_mp4_module 
--with-http_gunzip_module --with-http_gzip_static_module 
--with-http_random_index_module --with-http_secure_link_module 
--with-http_stub_status_module --with-http_auth_request_module 
--with-mail --with-mail_ssl_module --with-file-aio 
--with-http_spdy_module --with-cc-opt='-g -O2 -fstack-protector-strong 
-Wformat -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2' 
--with-ld-opt='-Wl,-z,relro -Wl,--as-needed' --with-ipv6
---