Windows Azure Role Communication

I have a few posts along the lines of scaling an Azure application, but thought I’d throw this tidbit out.  You might be developing your own management system for your Azure deployments, and in doing so, having visibility into the roles running within your deployment is very handy.   The idea behind this series of posts is to ultimately explore how to get visibility into roles, and then a few ways we can tackle inter-role communication. 

The first task is to define internal endpoints for each of our roles.  If you don’t do this, you will only have visibility into the current role.  So, if you have a single role solution (any number of instances) than you don’t have to do this. 

Let's take a pretty simple example where we want to enumerate all the roles in our deployment, and their instances:

foreach (var appRole in RoleEnvironment.Roles)
{
    var instances = RoleEnvironment.Roles[appRole.Key].Instances;

    foreach (var instance in instances)
    {
        Response.Write(instance.Id);
    }
}

While this code will work fine, by default it will only show you the instances for the current role – other roles will show an instance count of zero.  Running this in my workerrole and trying to enumerate my webroles, I see this:

image

What we can do is define and internal endpoint for our roles that will allow this data to be discoverable.  In Visual Studio, it’s simply a matter of going into the properties of the role and defining an internal endpoint:

image

And we’re done.  Debugging the solution again:

image

We can do the same for our workerroles to be discoverable by other webroles, etc. 

In some future posts, I’ll build off this idea for doing some lightweight service management and role communication.

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