title: Node: "Error setting TTL index on collection" when using connect-mongo for sessions
body: <p>I am trying to deploy an Express app to heroku and get the following error:</p>
  
  <pre><code>2013-01-28T12:44:55+00:00 heroku[web.1]: Starting process with command `coffee    server.coffee`
  2013-01-28T12:44:57+00:00 app[web.1]: Express server listening on port 13715
  2013-01-28T12:44:57+00:00 app[web.1]: /app/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/connection/server.js:537
  2013-01-28T12:44:57+00:00 app[web.1]:               ^
  2013-01-28T12:44:57+00:00 app[web.1]:         throw err;
  2013-01-28T12:44:57+00:00 app[web.1]:     at Db.indexInformation (/app/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/db.js:1372:30)
  2013-01-28T12:44:57+00:00 app[web.1]: Error: Error setting TTL index on collection : sessions
  2013-01-28T12:44:57+00:00 app[web.1]:     at module.exports._get_collection (/app/node_modules/connect-mongo/lib/connect-mongo.js:137:23)
  2013-01-28T12:44:57+00:00 app[web.1]:     at Cursor.toArray (/app/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/cursor.js:152:22)
  2013-01-28T12:44:57+00:00 app[web.1]:     at Db.ensureIndex (/app/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/db.js:1228:28)
  2013-01-28T12:44:57+00:00 app[web.1]:     at Cursor.nextObject.self.queryRun (/app/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/cursor.js:594:39)
  2013-01-28T12:44:57+00:00 app[web.1]:     at Db._executeQueryCommand (/app/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/db.js:1814:5)
  2013-01-28T12:44:57+00:00 app[web.1]:     at Cursor.close (/app/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/cursor.js:947:5)
  2013-01-28T12:44:57+00:00 app[web.1]:     at Cursor.nextObject.commandHandler (/app/node_modules/connect-mongo/node_modules/mongodb/lib/mongodb/cursor.js:594:21)
  2013-01-28T12:44:57+00:00 app[web.1]:     at EventEmitter.emit (events.js:126:20)
  2013-01-28T12:44:57+00:00 app[web.1]:     at g (events.js:192:14)
  </code></pre>
  
  <p>When i run this locally, it works fine. In both cases, I am connecting to MongoHQ.
  Here are the relevant parts of my server.coffee:</p>
  
  <pre><code>express          = require 'express'
  mongoStore       = require("connect-mongo")(express)
  
  app.configure -&gt;
    app.use express.errorHandler()
    app.use express.logger("dev")
    app.use express.bodyParser()
    app.use express.methodOverride()
    app.use express.cookieParser(config.cookieSecret)
    app.use express.session(
      secret: config.sessionSecret
      cookie:
        httpOnly:         true
        secure:           true
      store: new mongoStore(
        url:              config.db
        collection:       "sessions"
        auto_reconnect:   true
      )
    )
    app.use express.csrf()
    app.use express.static(config.root + "/public")
    app.use assets()
    app.use flash()
  
    app.use passport.initialize()
    app.use passport.session()
  
    app.use app.router
  </code></pre>
  
  <p>I am using node 0.8.14, express 3.0.3, mongoose 3.4.0, connect-mongo 0.3.2.
  Any help would be greatly appreciated!</p>