Add the "demo1" example app

This just adds a simple voting app for the demo script.  It leverages
a Node.js Express app for the frontend and a MongoDB database for the backend.
It conditionally provisions and attaches to an AWS Elastic Block Store volume
in the event that it's targeting an AWS cluster, and ephemeral storage otherwise.

examples/demo1/.gitignore

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+node_modules/
+

examples/demo1/Dockerfile

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+FROM node:argon
+
+# Create app directory
+RUN mkdir -p /usr/src/app
+WORKDIR /usr/src/app
+
+# Install app dependencies
+COPY package.json /usr/src/app/
+RUN npm install
+
+# Bundle app source
+COPY . /usr/src/app
+
+EXPOSE 8080
+CMD [ "npm", "start" ]
+

examples/demo1/Mu.yaml

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+name: demo1-example
+description: A simple Express voting app with a MongoDB backend, ready for production use.
+services:
+    private:
+        {{if aws .target}}
+            - aws/ebs/volume
+        {{done}}
+        - mongodb/mongodb
+            {{if aws .target}}
+                volume: @volume
+            {{done}}
+    public:
+        - app:
+            type: mu/container
+            build: .
+            arguments:
+                db: @mongodb
+

examples/demo1/README.md

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+# examples/demo1
+
+A simple Express voting app with a MongoDB backend, ready for production use.
+
+It supports two web APIs:
+
+1. GET /, prints out the current vote counts.
+2. POST /vote, casts your vote for a particular candidate.
+

examples/demo1/app.js

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+"use strict";
+
+var express = require("express");
+var bodyParser = require("body-parser");
+var mongodb = require("mongodb");
+
+// First read in the arguments.
+if (process.argv.length < 3) {
+    console.log("Missing required database argument");
+    process.exit(-1);
+}
+
+var db = process.argv[2];
+
+// Connect to the database and then fire up an Express app.
+mongodb.MongoClient.connect(`mongodb://${db}`, (err, conn) => {
+    if (err) {
+        console.log(`Problem connecting to database ${db}:`);
+        console.log(err);
+        process.exit(-1);
+    }
+
+    var votes = conn.collection("votes");
+
+    var app = express();
+    app.use(bodyParser.json());
+
+    app.get("/", (req, res) => {
+        votes.aggregate([ { "$group" : { _id: "$candidate", count: { $sum: 1 } } } ]).toArray(
+            (err, candidates) => {
+                // TODO: sort?
+                if (err) {
+                    res.status(500).send(`An error occurred: ${err}`);
+                } else {
+                    res.send(JSON.stringify(candidates, null, 4));
+                }
+            }
+        );
+    });
+
+    app.post("/vote", (req, res) => {
+        var vote = req.body;
+        if (!vote || !vote.candidate) {
+            res.status(500).send("Missing candidate in POST body");
+        } else {
+            votes.insertOne(
+                { candidate: vote.candidate, time: Date.now() },
+                (err) => {
+                    if (err) {
+                        res.status(500).send(`An error occurred: ${err}`);
+                    } else {
+                        res.status(200);
+                    }
+                }
+            );
+        }
+    });
+
+    app.listen(8080, () => {
+        console.log("App listening on port 8080");
+    });
+});
+

examples/demo1/package.json

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+{
+  "name": "demo1",
+  "version": "0.0.1",
+  "description": "A simple Express voting app with a MongoDB backend, ready for production use.",
+  "main": "app.js",
+  "dependencies": {
+    "body-parser": "^1.15.2",
+    "express": "^4.14.0",
+    "mongodb": "^2.2.11"
+  }
+}