CODEWITHSUNDEEP
azureazure-web-roles
Pittsburgh DBA
Pittsburgh DBA

Reputation: 6773

Azure Web Role Internal Endpoint - Not Load Balanced

The Azure documentation says that internal endpoints on a web role will not be load balanced. What is the practical ramification of this?

Example: I have a web role with 20 instances. If I define an internal endpoint for that web role, what is the internal implementation? For example, will all 20 instances still service this end point? Can I obtain a specific endpoint for each instance?

We have a unique callback requirement that could be nicely served by utilizing the normal load balancing behavior on the public endpoint, but having each instance expose an internal endpoint. Based on the published numbers for endpoint limits, this is not possible. So, when defining an internal endpoint, is it "1 per instance", or what? Do all of the role instances service the endpoint? What does Microsoft mean when they say that the internal endpoint is not load balanced? Does all the traffic just flow to one instance? That does not make sense.

Upvotes: 2

Views: 6574

Answers (3)

user94559
user94559

Reputation: 60143

Just trying to make things more concise and concrete:

// get a list of all instances of role "MyRole"
var instances = RoleEnvironment.Roles["MyRole"].Instances;

// pick an instance at random
var instance = instances[new Random().Next(instances.Count())];

// for that instance, get the IP address and port for the endpoint "MyEndpoint"
var endpoint = instance.InstanceEndpoints["MyEndpoint"].IPEndpoint;

Think of internal endpoints as a discovery mechanism for finding your other VMs.

Upvotes: 3

Neil Mackenzie
Neil Mackenzie

Reputation: 2847

The endpoints are defined at the role level and instantiated for each instance.

An input endpoint has a public IP address making it accessible from the internet. Traffic to that input endpoint is load-balanced (with a round-robin algorithm) among all the instances of the role hosting the endpoint.

An internal endpoint has no public IP address and is only accessible from inside the cloud service OR a virtual network including that cloud service. Windows Azure does not load balance traffic to internal endpoints - each role instance endpoint must be individually addressed. Ryan Dunn has a nice post showing a simple example of implementing load balanced interaction with an internal endpoint hosting a WCF service.

The Spring Wave release introducted a preview of an instance input endpoint, which is a public IP endpoint that is port forwarded to specific role instance. This, obvously, is not load balanced but provides a way to directly connect to a specific instance.

Upvotes: 3

astaykov
astaykov

Reputation: 30903

First let's clarify the numbers and limitations. The limitations for EndPoints is for Roles, not for Instances. If you are not sure, or still confusing Roles and Instances terms, you can check out my blog post on that. So, the limit is Per Role(s).

Now the differences between the EndPoints - I have a blog post describing them here. But in a quick round, Internal EndPoint will only open communication internally within the deployment. That's why it is Internal. No external traffic (from Internet) will be able to go to an Internal Endpoint. In that terms, it is not load balanced, because no traffic goes via/through a load balancer! The traffic of internal EndPoints only goes between Role Intances (eventually via some internal routing hardwere) but never lives a deployment boundaries. Having said that, it must already be clear that no Internet traffic can be sent to an Internal EndPoint.

A side note - InputEndpoint however is discoverable from Internet and from Inside the deployment. But it is LoadBalanced, since the traffic to an InputEndpoint comes via/through the LoadBalancer from the Internet.

Back to the Numbers. Let's say you have 1 WebRole with 1 Input EndPoint and 1 Internal EndPoint. That makes a total of 2 EndPoints for your deployment. Even if you spin up 50 instances, you sill have just 2 EndPoints that count toward the total EndPoints limit.

Can you obtain a specific EndPoint for Specific Instace - certainly yes! via the RoleEnvironemnt class. It has Roles enumeration. Each Role has Instances, and each Instance has InstanceEndpoints.

Hope this helps!

Upvotes: 12

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