How to store variables in Google Cloud Platform

Question

How can I store a variable in Google Cloud Platform? Right now I am using a global variable that my routes share, but the values are off every time a request has been made to the route. I think it's because my server may have multiple instances running sharing the same variable. My application is using Node.js/Express.

My POST route sets the new_posted_time variable that /display-message uses:

var new_posted_time = 0;
app.post('/message', function (request, response) {
  message = request.body.Body;

  new_posted_time = new_posted_time + 1;

  console.log("This is the new time from POST: " + new_posted_time);
  response.send("<Response><Message>Heyyo!</Message></Response>");

});

My GET route gets the value for new_posted_time that was defined in /message .

app.get('/display-message', function(req,res){

    var last_updated_time = req.query.last_updated;

    function checkMessage() {
        var new_time = new_posted_time;
        console.log("Checking messaged with new time from GET: " + new_time);

        if(!last_updated_time || last_updated_time < new_time) {
            updateMessage(new_time);
        }
        else {
            console.log("No new messages at this time");
            myTimeout = setTimeout(function(){
                checkMessage(res);
            }, 1000 * 10); //10 seconds
        }
    }

    function updateMessage() {
        console.log("Updating message now");
        var output = {
            success: 1,
            data: message,
            old_stamp: last_updated_time,
            new_stamp: new_stamp
        };

        return res.json(output);
    }

    checkMessage();

});

So I need to be able to store the shared variable new_posted_time somewhere in Google's database because the value is not consistent every time my application runs due to many instances running (which is my guess).

Answer 1

You should probably store 'state' like this in a persistent store like Google Cloud Datastore . Here is an article on implementing counters with Google Cloud Datastore (its from the AppEngine Datastore API, but it is the same principle).

Storing state in your instances is a bad idea because not only will you have consistency problems between instances, you will also lose data when an instance is shutdown automatically by AppEngine.