10. Load balancers

Load balancers are used to support scaling and high availability for applications and services. A load balancer is primarily composed of three components—a frontend, a backend, and routing rules. Requests coming to the frontend of a load balancer are distributed based on routing rules to the backend, where we place multiple instances of a service. This can be used for performance-related reasons, where we would like to distribute traffic equally between endpoints in the backend, or for high availability, where multiple instances of services are used to increase the chances that at least one endpoint will be available at all times.

We will cover the following recipes in this chapter:

• Creating an internal load balancer
• Creating a public load balancer
• Creating a backend pool
• Creating health probes
• Creating load balancer rules
• Creating inbound NAT rules
• Creating explicit outbound rules

Technical requirements

For this chapter, an Azure subscription is required.

The code samples can be found at https://github.com/PacktPublishing/Azure-Networking-Cookbook-Second-Edition/tree/master/Chapter10.

Creating an internal load balancer

Microsoft Azure supports two types of load balancers—internal and public. An internal load balancer is assigned a private IP address (from the address range of subnets in the virtual network) for a frontend IP address, and it targets the private IP addresses of our services (usually, an Azure virtual machine (VM)) in the backend. An internal load balancer is usually used by services that are not internet-facing and are accessed only from within our virtual network.

Getting ready

Before you start, open the browser and go to the Azure portal via https://portal.azure.com.

How to do it...

In order to create a new internal load balancer with the Azure portal, we must use the following steps:

1. In the Azure portal, select Create a resource and choose Load Balancer under Networking services (or search for Load Balancer in the search bar).
2. In the new pane, we must select a Subscription option and a Resource group option for where...

Creating a public load balancer

The second type of load balancer in Azure is a public load balancer. The main difference is that a public load balancer is assigned a public IP address in the frontend, and all requests come over the internet. The requests are then distributed to the endpoints in the backend.

Getting ready

Before you start, open the browser and go to the Azure portal via https://portal.azure.com.

How to do it...

In order to create a new public load balancer with the Azure portal, we must follow these steps:

1. In the Azure portal, select Create a resource and choose Load Balancer under Networking services (or search for Load Balancer in the search bar).
2. In the new pane, we must select a Subscription option and a Resource group option for where the load balancer is to be created. Then, we must provide information for Name, Region, Type, and SKU. In this case, we select Public for Type to deploy a public load balancer. and set SKU to Standard. Selecting...

Creating a backend pool

After the load balancer is created, either internally or publicly, we need to configure it further in order to start using it. During the creation process, we define the frontend of the load balancer and know where traffic needs to go to reach the load balancer. But, in order to define where that traffic needs to go after reaching the load balancer, we must first define a backend pool.

Getting ready

Before you start, open the browser and go to the Azure portal via https://portal.azure.com.

How to do it...

In order to create the backend pool, we must do the following:

1. In the Azure portal, locate the previously created load balancer (either internal or public).
2. In the Load balancer pane, under Settings, select Backend pools. Select Add to add the new backend pool:
   

   Figure 10.3: Adding a new backend pool

3. In the new pane, we must provide a Name and specify what the load balancer is associated to. Associations can be created for VMs or VM...

Creating health probes

After the frontend and the backend of the load balancer are defined, traffic is evenly distributed among endpoints in the backend. But what if one of the endpoints is unavailable? In that case, some of the requests will fail until we detect the issue, or even fail indefinitely should the issue remain undetected. The load balancer would send a request to all the defined endpoints in the backend pool and the request would fail when directed to an unavailable server.

This is why we introduce the next two components in the load balancer—health probes and rules. These components are used to detect issues and define what to do when issues are detected.

Health probes constantly monitor all endpoints defined in the backend pool and detect if any of them become unavailable. They do this by sending a probe in the configured protocol and listening for a response. If an HTTP probe is configured, an HTTP 200 OK response is required to be considered successful...

Creating load balancer rules

The last piece of the puzzle when speaking of Azure load balancers is the rule. Rules finally tie all things together and define which health probe (there can be more than one) will monitor which backend pool (more than one can be available). Furthermore, rules enable port mapping from the frontend of a load balancer to the backend pool, defining how ports relate and how incoming traffic is forwarded to the backend.

Getting ready

Before you start, open your browser and go to the Azure portal via https://portal.azure.com.

How to do it...

In order to create a load balancer rule, we must do the following:

1. In the Azure portal, locate the previously created load balancer (either internal or public).
2. In the Load balancer pane, under Settings, select Load balancing rules. Select Add to add a load balancing rule:
   

   Figure 10.10: Adding load balancing rules

3. In the new pane, we must provide information for the Name and the IP version...

Creating inbound NAT rules

Inbound Network Address Translation (NAT) rules are an optional setting in Azure Load Balancer. These rules essentially create another port mapping from the frontend to the backend, forwarding traffic from a specific port on the frontend to a specific port in the backend. The difference between inbound NAT rules and port mapping in load balancer rules is that inbound NAT rules apply to direct forwarding to a VM, whereas load balancer rules forward traffic to a backend pool.

Getting ready

Before you start, open the browser and go to the Azure portal via https://portal.azure.com.

How to do it...

In order to create a new inbound NAT rule, we must do the following:

1. In the Azure portal, locate the previously created load balancer (either internal or public).
2. In the Load balancer pane, under Settings, select Inbound NAT rules. Select Add to add a new inbound NAT rule:
   

   Figure 10.12: Adding an inbound NAT rule for an existing load balancer

...

Creating explicit outbound rules

When creating load balancing rules, we can create implicit outbound rules. This will enable Source Network Address Translation (SNAT) for VMs in the backend pool and allow them to access the internet over the load balancer's public IP address (specified in the rule). But in some scenarios, implicit rules are not enough and we need to create explicit outbound rules. Explicit outbound rules (and SNAT in general) are available only for public load balancers with the Standard SKU.

Getting ready

Before we begin, make sure that implicit outbound rules are disabled from load balancing rules:

Figure 10.14: Disabling implicit outbound rules

Now, open the browser and go to the Azure portal via https://portal.azure.com.

How to do it...

In order to create a load balancer rule, we must do the following:

1. In the Azure portal, locate the previously created public load balancer.
2. In the Load balancer pane, under...