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Different ways to access Azure instances using Public IP

Let's talk about IP Addressing in Microsoft Azure. In this post we will talk about ILPIP (Instance-Level Public IP, used to be known as PIP - Public IP) and Reserved  Public IP (that is a new feature of offered by Microsoft Azure).

Virtual IP (VIP)
Before jumping into this subject, we need to understand what is a Virtual IP (VIP).
A Virtual IP is a public IP that is assigned to a resource like Web Role, Worker Role or Virtual Machine in the moment when we create a cloud service. This VIP is allocated automatically and allow our resource to communicate with external resource. Using VIP, a request from internet can access our Azure Resource.
This VIP will never change as long as the cloud contains at least one instance of that resources. For example we can have 10 instances of Web Roles with a specific deployment. As long as we have at least one, we will not lose the IP. Only when we deprovision the resource we will lose the VIP.
A "fix" for this issue, before having Reserved Public IP was to have all the time a small instance of resources allocated all the time - a small and cheap hack.

Using VIP you could connect directly to an instance of your resource only if you would allocate use the VIP and a Port Number. For each instance of your resource you can assign a specific port. As showed below.

Instance-Level Public IP (ILPIP)
This IP can be assigned directly to your instance of your resource (like VM). In this way you can target directly your instance and not the cloud services. Basically it allow us to connect and communicate directly to a specific instance of our resource (directly to a Web Role, Worker Role or Virtual Machine instance).
For example we can connect directly from internet to a VM instance, like in the diagram below.

Even if we can access an instance of our resource directly from internet using a 'Public IP', we still cannot have a fixed and dedicated IP if you recreate your resource. The story is similar with the one from Virtual IP (VIP).

Reserved IP
This feature allows us to reserve a fixed IP to our cloud resource. This means that we can have in front of our Azure resources a public IP that will not change in time, even if we stop or reallocate this resources.

This solution is more similar with Virtual IP because the Reserved IP is in front of our cloud services. There is no public IP reserved for each instance of your cloud services. Only one public IP will be reserved for all cloud services.
This means that if you want to access a specific instance, you will need a similar solution with Virtual IP, where you map a port to a specific instance.

Based on our needs we can reserved a public IP for our cloud services or not. We should be aware that we can control at IP level only for Web Roles, Worker Roles and VMs. For Azure Services like Azure Storage, Service Bus of Event Hub we don't have any kind of control.


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