Building SaaS Solutions on Windows Azure

Steve Marx

Who am I?

  • Early Windows Azure team member
  • Chief Cloud Architect for Aditi
  • Also founded site44.com, building SaaS
    (but not on Windows Azure)

Self-Promotion Warning

Agenda

  • Defining Software as a Service
  • SaaS architectures and multi-tenancy
  • SaaS billing and metering

SaaS: a Working Definition

software delivered over the internet, billed on a subscription basis
- Steve Marx, today

SaaS Multi-tenancy

SaaS is commonly multi-tenant

  • Resources are shared among users
  • Sometimes users belong to (customized) tenants

Multi-tenancy Tradeoffs

  • Multi-tenant
    • Pros: resource-efficient, low operational cost
    • Cons: difficult implementation, isolation challenges
  • Single-tenant
    • Pros: easy to implement (particularly for migrations), isolated
    • Cons: less efficient, more things to manage

Multi-tenancy and N-Tier Architecture

N-tier architecture:

  1. Client – typically single-tenant
  2. Service(s) – multi-tenant or not
  3. Data – multi-tenant or not

For each tier, multi-tenancy means sharing resources

Multi-tenancy in Identity

Approach boils down to one of:

  • Log users in, look up their tenant
  • Users go directly to tenant and log in

Access Control and Active Directory Federation help.

Multi-tenancy in Services

Three options these days:

  • Web Sites
    • Shared model good for single-tenant
    • Dedicated model similar to cloud services
  • Cloud Services
    • Good isolation boundary
    • Costly and non-trivial to spin up new services
  • Virtual Machines
    • In fact, these are cloud services

Demo

Multi-tenant Web Sites and Access Control

smarxfs.azurewebsites.net

Web.config:

<authentication mode="Forms">
  <forms loginUrl="https://smarxte12.accesscontrol.windows.net:443/..."
    timeout="2880" />
</authentication>

LoginController.cs:

[HttpPost]
[ValidateInput(false)]
public ActionResult Index(string wresult)
{
  ...
  FormsAuthentication.SetAuthCookie(...);

Multi-tenancy in Data: WA Storage

  1. One account per tenant
    • Best isolation
    • Limited number of accounts per subscription
  2. One partition per tenant
    • Typically easily to implement
    • Good performance isolation
    • Limited management and security isolation
  3. External/no isolation

Multi-tenancy in Data: SQL

  • One database per tenant
    • Good performance isolation
    • Can be expensive
  • One table per tenant
    • Helps query isolation
    • A bit awkward to implement
  • Federation (horizontal partitioning)
    • Good security isolation
    • Good scalability
    • Some performance isolation

Demo

Multi-tenant blob storage

smarxfs.azurewebsites.net 
var container =
  blobs.GetContainerReference(
    User.Identity.Name);

return View(
  container.ListBlobs()
  .OfType<CloudBlob>()
  .Select(b =>
    b.Uri.AbsoluteUri +
    b.GetSharedAccessSignature(...)));

SaaS Business Models

General strategy:

  1. Figure out your costs.
  2. Charge more than that.

A few popular approaches:

  • Tiered pricing plans (e.g. freemium)
  • Flat rate, optionally with usage caps
  • Utility billing

Who Runs the Service?

Single-tenant model gives you two options:

  • You run the service and bill your customer.
  • Your customer runs the service. (And optionally, you manage it.)

How to Bill

  • Store – discovery plus billing
    • Windows Azure Marketplace
    • Mobile app stores
    • Windows Store
  • Payment processor
    • PayPal
    • Stripe
    • Recurly

Billing Considerations

  • Ease of integration
  • Discoverability from a marketplace
  • Customer UI (viewing bills, dispute resolution, etc.)

Things to Measure

  • Don't try to count CPU cycles
  • Possibly count VM hours
  • Possibly count bandwidth
  • Possibly count data size

How to Measure

  • Log what you need to measure
    • Use built-in Diagnostics
    • Roll your own
  • Use WA storage analytics/logging
    • Can help with bandwidth measurements
    • Measures capacity, but only at account level
  • Use billing data (last resort)
    • Delayed
    • Not easy to consume

Demo

Roll-your-own metering

smarxfs.azurewebsites.net

Bonus: Site44 Architecture and Business Model

Multi-tenant everything:

  • Scaled-out caching tier (Varnish)
  • Scaled-out web server
  • Structured database (DynamoDB)
  • Replicated in-memory database/cache (Redis)

Freemium with capped usage

Summary/Advice

  • Decide about per-tier tenancy, considering:
    • cost
    • isolation requirements
  • Decide on a business model, considering:
    • your costs
    • what customers want
    • what you can measure
  • Use Windows Azure where possible

Questions?

Ask now or contact me later: