Cloud database for Azure multi-tenant application?

Question

I am starting to port one old desktop single tenant application into the cloud and wish to hear what would be your recommendation about the databases for my cloud-based multi-tenant application?

My basic requirement is simple:

1. For each tenant, its data is separate to any other tenants' data. I can easily backup, restore, export the data for one single tenant without affecting other tenants.
2. I don't really want to care about multi-tenancy in the business logic code. It should look like a single tenant application behind the security layer, no tenant ID pass around etc.
3. Easy to query using some mature technology like LINQ.
4. Availability and scalability, of course, easy to set up replicas, fail-over and scaling up and down etc.

I have gone through some investigations about multi-tenant application development. I have noticed SQL databases from Azure and AWS are both very expensive(the cost for just SQL database instance is close to the license fee of the original application), so I definitely can't use separate SQL database instances for tenants.

Now I'm reading this book Developing Multi-tenant Applications for the Cloud, 3rd Edition, and it uses Azure Storage Service to implement multi-tenancy. I haven't finished the book yet, it seems you still have to handle the multi-tenancy by yourself and the sample code is already out of date.

I have seen lots of SO questions compare Azure Table Storage with MongoDB. The MongoDB is very new to me, not sure whether it could be easily used to fulfill my requirements?

And I have seen RavenDB as well, it does support multi-tenancy out of box. But I didn't see some good sample code about how to use it in Azure app development.

Hope to hear some good advices from awesome SO guys.

Answer 1

I would better opt with RavenDB on top of MongoDB. Even Raven is a new comer in to the game, it supports most of the features which traditional SQL supports.

Also to make up a decisions the volume of data you are dealing is a also a key decision pointer. Also the amount of traffic you are expecting.

Also keep in mind that operational costs and development efforts. HA and DR scenarios can be problematic when you use Raven or Mongo because of the fact that you need to host them. But when it comes to Azure Storage, it by defaults protects you to a maximum extent by maintaining 3 copies of information.

So I would suggest you to carefully make the trade offs and opt wisely based on your business needs, cost optimization, development and operational effort.

Answer 2

Having a single instance of your application for each tenant is a very expensive way to implement an application, however I realise that if an application was developed with a single tenant in mind, then the costs of changing over can be high.

First can we start out with why you have a desktop application connecting to a database at another location. The latency can really slow down an application. Ideally you would want a locally installed database and have it sync with the cloud DB, or add in appropriate caching into your application.

However the DB would still need to differentiate the clients.

Why do you need this to go to a cloud database? Is it for backup purposes, not installing a DB locally on a clients machine, accessing the same data from many machines or something else?

Unless your application is extremely large, I would recommend rewriting it for multi-tenant to one SQL Azure database. The architecture chosen at the beginning of the project doesn't suit your requirements now. As you expand you will run into further issues.