Add http cluster example

examples/cluster-httpd/README.md

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+
+# Socket.IO Chat with httpd & redis
+
+A simple chat demo for socket.io
+
+## How to use
+
+Install [Docker Compose](https://docs.docker.com/compose/install/), then:
+
+```
+$ docker-compose up -d
+```
+
+And then point your browser to `http://localhost:3000`.
+
+This will start four Socket.IO nodes, behind a httpd proxy which will loadbalance the requests (using a cookie for sticky sessions, see [cookie](http://httpd.apache.org/docs/2.4/fr/mod/mod_proxy_balancer.html)).
+
+Each node connects to the redis backend, which will enable to broadcast to every client, no matter which node it is currently connected to.
+
+```
+# you can kill a given node, the client should reconnect to another node
+$ docker-compose stop server-george
+```
+
+## Features
+
+- Multiple users can join a chat room by each entering a unique username
+on website load.
+- Users can type chat messages to the chat room.
+- A notification is sent to all users when a user joins or leaves
+the chatroom.

examples/cluster-httpd/docker-compose.yml

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+
+httpd:
+  build: ./httpd
+  links:
+    - server-john
+    - server-paul
+    - server-george
+    - server-ringo
+  ports:
+   - "3000:80"
+
+server-john:
+  build: ./server
+  links:
+    - redis
+  expose:
+    - "3000"
+  environment:
+    - NAME=John
+
+server-paul:
+  build: ./server
+  links:
+    - redis
+  expose:
+    - "3000"
+  environment:
+    - NAME=Paul
+
+server-george:
+  build: ./server
+  links:
+    - redis
+  expose:
+    - "3000"
+  environment:
+    - NAME=George
+
+server-ringo:
+  build: ./server
+  links:
+    - redis
+  expose:
+    - "3000"
+  environment:
+    - NAME=Ringo
+
+redis:
+  image: redis:alpine
+  expose:
+    - "6379"

examples/cluster-httpd/httpd/Dockerfile

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+FROM httpd:2.4-alpine
+COPY ./httpd.conf /usr/local/apache2/conf/httpd.conf

examples/cluster-httpd/httpd/httpd.conf

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+
+Listen 80
+
+ServerName localhost
+
+LoadModule authn_file_module            modules/mod_authn_file.so
+LoadModule authn_core_module            modules/mod_authn_core.so
+LoadModule authz_host_module            modules/mod_authz_host.so
+LoadModule authz_groupfile_module       modules/mod_authz_groupfile.so
+LoadModule authz_user_module            modules/mod_authz_user.so
+LoadModule authz_core_module            modules/mod_authz_core.so
+
+LoadModule headers_module               modules/mod_headers.so
+LoadModule lbmethod_byrequests_module   modules/mod_lbmethod_byrequests.so
+LoadModule proxy_module                 modules/mod_proxy.so
+LoadModule proxy_balancer_module        modules/mod_proxy_balancer.so
+LoadModule proxy_http_module            modules/mod_proxy_http.so
+LoadModule proxy_wstunnel_module        modules/mod_proxy_wstunnel.so
+LoadModule rewrite_module               modules/mod_rewrite.so
+LoadModule slotmem_shm_module           modules/mod_slotmem_shm.so
+LoadModule unixd_module                 modules/mod_unixd.so
+
+User daemon
+Group daemon
+
+ErrorLog /proc/self/fd/2
+
+Header add Set-Cookie "SERVERID=sticky.%{BALANCER_WORKER_ROUTE}e; path=/" env=BALANCER_ROUTE_CHANGED
+
+<Proxy "balancer://nodes_polling">
+    BalancerMember "http://server-john:3000"    route=john
+    BalancerMember "http://server-paul:3000"    route=paul
+    BalancerMember "http://server-george:3000"  route=george
+    BalancerMember "http://server-ringo:3000"   route=ringo
+    ProxySet stickysession=SERVERID
+</Proxy>
+
+<Proxy "balancer://nodes_ws">
+    BalancerMember "ws://server-john:3000"    route=john
+    BalancerMember "ws://server-paul:3000"    route=paul
+    BalancerMember "ws://server-george:3000"  route=george
+    BalancerMember "ws://server-ringo:3000"   route=ringo
+    ProxySet stickysession=SERVERID
+</Proxy>
+
+RewriteEngine On
+RewriteCond %{HTTP:Upgrade} =websocket [NC]
+RewriteRule /(.*) balancer://nodes_ws/$1 [P,L]
+RewriteCond %{HTTP:Upgrade} !=websocket [NC]
+RewriteRule /(.*) balancer://nodes_polling/$1 [P,L]
+
+ProxyTimeout 3