Add sample for using memcached for connect session state

appengine/express-memcached-session/README.md

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+# Express + Memcached Sessions -> Google App Engine
+
+This is a simple guide to using memcached for session state while running [expressjs](http://expressjs.com/) on Google App Engine.  Each Google App Engine application comes with a memcached service instance, which can be reached with a standard memcached driver at `memcache:11211`.
+
+1. [Create a new Express app](http://expressjs.com/starter/generator.html)
+
+2. Create an `app.yaml` in the root of your application with the following contents:
+
+    ```yaml
+    runtime: nodejs
+    vm: true
+    env_variables:
+      PORT: 8080
+      MEMCACHE_URL: memcache:11211
+    ```
+
+    Notice the MEMCACHE_URL environment variable - this is where you can reach your standard memcached cluster across instances. 
+
+3. Use the [connect-memcached](https://github.com/balor/connect-memcached) module.  Run `npm install --save connect-memcached`, and add the following to your server.js or app.js:
+
+    ```js
+    var MemcachedStore = require('connect-memcached')(session);
+    ...
+    app.use(session({
+        secret: 'appengineFTW',
+        key: 'test',
+        proxy: 'true',
+        store: new MemcachedStore({
+            hosts: [process.env.MEMCACHE_URL || '127.0.0.1:11211']
+        })
+    }));
+    ```
+4. In your express route handlers, you can now safely use `req.session.*` across multiple nodejs instances:
+
+    ```js
+    app.get('/', function(req, res){
+        publicIp.v4(function (err, ip) {
+            res.write("<div>" + ip + "</div>");
+            if(req.session.views) {
+                ++req.session.views;
+            } else {
+                req.session.views = 1;
+            }
+            res.end('Viewed <strong>' + req.session.views + '</strong> times.');
+        });
+    });
+    ```
+
+5. To test the sample locally, you can install memcached.  
+    - OSX + [Brew](http://brew.sh/): `brew install memcached`
+    - Windows + [Chocolatey](https://chocolatey.org/packages/memcached): `choco install memcached`
+
+    Run memcached on localhost:11211 by running `memcached`
+
+
+6. Deploy your app. For convenience, you can use an npm script to run the command. Modify your `package.json` to include:
+
+    ```js
+    "scripts": {
+      "start": "node server.js",
+      "deploy": "gcloud preview app deploy app.yaml --set-default --project [project id]"
+    }
+    ```
+
+At the terminal you can now run `npm run deploy` to deploy your application.

appengine/express-memcached-session/app.yaml

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+# Copyright 2015, Google, Inc.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+runtime: nodejs
+api_version: 1
+vm: true
+env_variables:
+  PORT: 8080
+  MEMCACHE_URL: localhost:11211

appengine/express-memcached-session/package.json

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+{
+  "name": "express-memcached-session-demo",
+  "version": "1.0.0",
+  "private": true,
+  "scripts": {
+    "deploy": "gcloud preview app deploy app.yaml --set-default --project express-memcached-demo"
+  },
+  "dependencies": {
+    "connect-memcached": "^0.1.0",
+    "cookie-parser": "~1.3.5",
+    "express": "~4.12.4",
+    "express-session": "^1.11.3",
+    "public-ip": "^1.1.0"
+  }
+}

appengine/express-memcached-session/server.js

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+// Copyright 2015, Google, Inc.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+'use strict';
+
+var express = require('express');
+var session = require('express-session');
+var cookieParser = require('cookie-parser');
+var http = require('http');
+var MemcachedStore = require('connect-memcached')(session);
+var publicIp = require('public-ip');
+
+var app = express();
+
+app.use(cookieParser());
+app.use(session({
+    secret: 'appengineFTW',
+    key: 'test',
+    proxy: 'true',
+    store: new MemcachedStore({
+        hosts: [process.env.MEMCACHE_URL || '127.0.0.1:11211']
+    })
+}));
+
+app.get('/', function(req, res){
+    publicIp.v4(function (err, ip) {
+
+        // This shows the IP for each 
+        res.write('<div>' + ip + '</div>');
+
+        if(req.session.views) {
+            ++req.session.views;
+        } else {
+            req.session.views = 1;
+        }
+        res.end('Viewed <strong>' + req.session.views + '</strong> times.');
+    });
+});
+
+http.createServer(app).listen(process.env.PORT || 8080, function() {
+    console.log('Listening on %d', this.address().port);
+});