High Availability

The availability of data and applications is a core requirement for any application, whether it is on-premises or in the cloud. If your data or application isn’t available to you, nothing else matters. There are many reasons why you may lose availability, but the most common issues are:

• A network outage

• An application failure

• A system, such as a virtual machine, outage

• A power outage

• A problem with a reliant system such as an external database

In a perfect world, you experience 100% availability, but if any of the above problems occur, that percentage will begin to decrease. Therefore, it’s critical that your infrastructure minimize the risk of problems that impact availability of your application.

Cloud providers offer a service-level agreement (SLA) that guarantees a certain level of availability as a percentage. An SLA will usually guarantee an uptime of close to 100%, but it only covers systems that are controlled by the cloud provider.

An application hosted in the cloud might be one that is developed by your company, but it can also be one provided to you by the cloud provider.

Scalability, elasticity, and agility

Computing resources aren’t free. Even if you’re using virtual machines, the underlying resources such as disk space, CPU, and memory cost money. The best way to minimize cost is to use only the resources necessary for your purposes. The challenge is that resource needs can change often and quickly.

Consider a situation where you are hosting an application in the cloud that tracks sales data for your company. If your sales staff regularly enter information on daily sales calls at the end of the day, you might need additional computing resources to handle that load. Those same resources aren’t needed during the day when the sales staff is making sales calls and not using the application.

You might also host a web application in the cloud that is used by external customers. Depending on the usage pattern, you might want to add additional computing resources on certain days or during certain times. You might also need to quickly adapt to more users if your company receives unexpected publicity from the media or some other means.

Scaling and elasticity allow you to easily deal with these kinds of scenarios. Scaling is the process of adding additional resources or additional power for your application. There are two variations of scaling: horizonal scaling (often referred to as scaling out) and vertical scaling (often referred to as scaling up).

When you scale out, you add additional VMs for your application. Each VM you add is identical to other VMs servicing your application. Scaling out provides additional resources to handle additional load.

When you scale up, you move to a new VM with additional resources. For example, you may determine that you need a more powerful CPU and more memory for your application. In that case, scaling up will allow you to move your application to a more powerful VM.

Figure 1-1 shows an example of scaling up a web application hosted in Azure.

Cloud providers make it easy to scale your application, and they offer the ability to scale automatically based on the usage pattern for your application. You can scale automatically based on things like CPU usage and memory usage, and you can also scale based on other metrics that are specific to the type of application. The concept of automatically scaling is referred to as elasticity.

One of major benefits of the cloud is that it allows you to quickly scale. For example, if you are running a web application in Azure and you determine that you need two more VMs for your application, you can scale out to three VMs in seconds. Azure takes care of allocating the resources for you. All you have to do is tell Azure how many VMs you want and you’re up and running. This kind of speed and flexibility in the cloud is often called cloud agility.

Fault tolerance and disaster recovery

In a complex cloud environment, things are bound to go wrong from time to time. In order to maintain a high level of availability, cloud providers implement systems that monitor the health of cloud resources and take action when a resource is determined to be unhealthy, thereby ensuring that the cloud is fault tolerant.

In addition to monitoring the health of VMs and other resources, cloud providers design their infrastructure in such a way as to ensure fault tolerance. For example, if you have an application running on two VMs in Azure, Microsoft ensures that those two VMs are allocated within the infrastructure so that they are unlikely to be impacted by system failures.

Fault tolerance is designed to deal with failure at a small scale; moving you, for example, from an unhealthy VM to a healthy VM. However, there are times when much larger failures can occur. For example, natural disasters in a region can impact all resources in that particular region. Not only can something like that impact availability, but without a plan in place, disasters can also mean the loss of valuable data.

Disaster recovery not only means having reliable backups of important data, but it also means that the cloud infrastructure can replicate your application’s resources in an unaffected region so that your data is safe and your application availability isn’t impacted. Disaster recovery plans are commonly referred to as Business Continuity and Disaster Recovery (BCDR) plans, and most cloud providers have services that can help you develop and implement a plan that works for your particular needs.

Economic benefits of the cloud

So far we’ve talked only about the availability benefit of moving to the cloud, but there are also economic benefits. Let’s consider both the on-premises model and the cloud model.

Infrastructure-as-a-Service (IaaS)

Infrastructure refers to the hardware that your application uses, and IaaS refers to the virtualized infrastructure offered by a cloud provider. When you create an IaaS resource, the cloud provider allocates a VM for your use. In some cases, the cloud provider might do the basic operating system install for you. In other situations, you may need to install the operating system yourself. In either case, you are responsible for installing other necessary services and your application.

Because you control the operating system install and installation of other services, IaaS gives you plenty of control over your cloud resources. However, it also means that you are responsible for making sure your operating system is patched with security updates, and if something goes wrong in the operating system, you’re responsible for troubleshooting it. The cloud provider is only responsible for providing the VM. You do, however, benefit from the underlying infrastructure in the area of fault tolerance and disaster recovery that we discussed earlier.

In Figure 1-3, you see an IaaS VM in the Azure portal. The Ubuntu Server, a Linux operating system, has been chosen for the VM. Once the VM is up and running, it will be using Ubuntu Server 18.04. Unless an updated is installed, it will always be running that version. Microsoft will never install patches or version updates for me.

Once you have an IaaS VM running in the cloud, you gain access to many services the cloud provider offers. For example, Microsoft offers Azure Security Center to ensure the security of your IaaS VMs, Azure Backup to make backing up data easy, Azure Log Analytics to help with troubleshooting any problems you might have, and much more.

IaaS services allow you to control costs effectively, because you only pay for them when you are using them. If you stop your IaaS VM, your billing stops for the resource. This makes IaaS an ideal choice if you need developers to have a platform for testing an application during release. Developers can start an IaaS VM, test the application as a team, and then stop the IaaS VM when testing is complete.

Another popular use of IaaS is when you need one or more powerful VMs for a temporary period. For example, you might need to analyze a large amount of data for a project. By utilizing IaaS VMs for your project, you can keep costs to a minimum, create resources quickly as you need them, and gain all the processing power you need.

IaaS services benefit from scaling and elasticity that we discussed earlier. If you need more VMs, you can scale out to accommodate that and then scale in when those resources are no longer needed. If you need more CPU power, more memory, or more disk space, you can quickly scale up to gain those benefits and then scale down when they’re no longer needed.

In a nutshell, IaaS services are a great choice if you want to let someone else manage the hardware infrastructure (which can include both the computers and the network) related to your application, but you want to maintain control of what’s installed in the operating system. In an IaaS environment, the cloud provider isn’t going to install something on the operating system for you, so the current state of what’s installed on your VMs is always known to you. If this is important for your particular needs, IaaS may be the right choice for you. IaaS is also a great choice if you occasionally need high-end VMs for specific needs.

IaaS is also a great choice if you want your application and configuration in the cloud, but you want the option of not paying for it when you aren’t using it. By stopping your VM, you can avoid the costs associated with it, and when you need to use your application again, you can simply start your VM and pick up right where you left off.

Platform-as-a-Service (PaaS)

In a PaaS environment, a cloud provider still provides the infrastructure for you, but they also provide the operating system, software installed in the operating system to help you connect to databases and network systems (often referred to as middleware), and many features that enable you to build and manage complex cloud applications.

PaaS sits right in the middle of the cloud pyramid. PaaS services offer you the flexibility of controlling the application, but they offload management and control of the underlying systems to the cloud provider. If you are deploying your own application to the cloud and you want to minimize your management investment, a PaaS service is often the best choice.

Suppose you need to run a web application that uses the PHP framework to connect to a back-end database system. If you were to choose IaaS for your application, you’d need to ensure that you install and configure PHP on your VM. You’d then need to install and configure the software necessary to connect to your back-end database. In a PaaS scenario, you simply deploy your web application to the cloud provider, and everything else is taken care of for you.

In Figure 1-4, we have a web application in Azure App Service, one of the PaaS offerings in Azure. It has been created on a VM that’s maintained by Microsoft. Notice the option of choosing either Linux or Windows, but the operating system is still managed by Microsoft. We also have the option of enabling Application Insights, a service in Azure that provides deep insight into how an application is performing, making it easier to troubleshoot problems if they occur.

One more interesting thing in Figure 1-4 is the option to publish either your code or a Docker image. Docker is a technology that makes it easy to package your application and the components that it requires into a container that you can then deploy and run on another computer in another environment, as long as that computer has Docker installed on it. In Azure App Service, I don’t have to worry about Docker installation or configuration. It’s automatically included on all App Service VMs as part of Microsoft’s PaaS offering, and it’s completely managed and maintained by Microsoft.

In a PaaS offering, cloud providers offer numerous application frameworks such as PHP, Node.js, ASP.NET, .NET Core, Java, Python, and more. The cloud provider usually provides multiple versions of each framework so you can choose a version that you know is compatible with your application. The cloud provider will also ensure that common components necessary for data connectivity from your application to other systems is installed and configured. That usually means that your application code works without you having to do any kind of complex configuration. In fact, this is one of the main benefits of using a PaaS service; you can often move your application from on-premises to a cloud environment by simply deploying it to the cloud. This concept is often referred to as lift-and-shift.

Because the cloud provider controls the operating system and what’s installed on the VM, they can provide additional capabilities to you by adding their own features. For example, suppose you want to add a log-in feature to your web application, and you want to allow users to log in with a Microsoft account, a Facebook account, or a Google account. If you wanted to add this capability on-premises, or in an IaaS environment, you need some developers to build it for you, a task that isn’t easy and one that requires specialized knowledge. You’d have to either have developers in your company who already have those skills, or you’d have to hire them. However, cloud providers often offer features like this in their PaaS services, and enabling them is as easy as flipping a switch and doing some minor configuration specific to your app.

A PaaS service also benefits from all of the other enhancements offered by the cloud; you get fault tolerance, elasticity, easy and quick scaling, backup and disaster recovery features, and more. In fact, features such as backing up and restoring data are oftentimes more user-friendly and feature-rich in a PaaS environment because the cloud provider installs customized software on the PaaS VMs to add functionality.

As you can see, there are real benefits to allowing the cloud provider to control what’s installed on the VMs running your application, but there can also be drawbacks. For example, the cloud provider controls when patches and updates are applied to both the operating system and to other components installed on the VMs. You’ll usually be given advance notice of major changes so that you can test your application on-premises first and avoid any downtime, but you do lose the flexibility and control of deciding when to update the VM.

Software-as-a-Service (SaaS)

As you’ve learned, IaaS requires you to control both the operating system and middleware components along with your application. When you move to PaaS, you offload the control of the operating system and middleware components to the cloud provider, and you’re responsible only for your application code. As you move to the top of the cloud pyramid and into the SaaS realm, the cloud provider controls everything. In other words, a SaaS service is software provided by a cloud provider that’s installed on infrastructure completely controlled by the hosting provider.

SaaS services offer you the flexibility of a pay-as-you-go model. Essentially, you rent your software from a service provider. Users of the software usually access the software from a web browser, but they may also install applications that will only work as long as you are paying for the SaaS service. One huge benefit of web-based software is that it works from just about any device, including smart phones. Because of that, SaaS services enable connectivity and productivity for field staff using devices they already own.

When using a SaaS service, not only do you benefit from using software written and maintained by someone else, but you can also benefit from allowing the cloud provider to maintain and configure the application. For example, if your company offers corporate email, you can choose to use Microsoft’s Office 365 SaaS service. By using the Exchange Online service in Office 365, you can take advantage of enterprise-ready email solutions without having to hire IT staff and build infrastructure to support it. Instead, Microsoft maintains the system for you. Not only do you benefit from the flexibility and reliability of the cloud, but you can also rest easy knowing that Microsoft is ensuring your Exchange services are always available to your users.

SaaS services aren’t just for the enterprise. In fact, most people use SaaS services all the time without even realizing it. If you use Hotmail or Gmail or another online email service, you’re using a SaaS service. The cloud provider hosts the email software in the cloud, and you log in and use that software using your web browser. You don’t have to know anything about the software. The cloud provider can offer new features with software updates, and those new features are available to you automatically without any action on your part. If the cloud provider finds a problem with the software, they can resolve it with a patch without you even realizing anything happened.

Comparing service types

We’ve already discussed some of the advantages and disadvantages of each type of cloud service, and the cloud pyramid provides a visual representation of how types of cloud services differ related to your responsibility and what you can control. In order to solidify these concepts, let’s look at a comparison of each service type.

As you’ve learned, IaaS provides you with the greatest flexibility. You can install your own software and your own components, and you control when the software and operating system are updated. An additional benefit is that you pay for your resources only when they’re being used, so IaaS has the ability to reduce your operational expenses. Even though you can save costs by turning off VMs you aren’t using, the higher costs associated with installing and maintaining your VMs might offset that benefit.

PaaS services offer you some of the same flexibility of IaaS services without the need to manage the infrastructure. In a PaaS service, you are responsible only for the application that’s installed in the cloud. This can be your own application, or an application developed by someone else (for example, a WordPress system or an e-commerce solution), but in either case, you are responsible for the application. PaaS services are popular for developer teams who are looking to move on-premises applications to the cloud easily and quickly, and they typically offer many different deployment options to make that as easy as possible. PaaS services also offer more features than IaaS services, because the cloud provider installs their own software and features on the platform. Any application running in a PaaS service, however, can be impacted by updates and version changes in the underlying software, and that can mean increased costs associated with testing an application before the cloud provider rolls out changes.

SaaS services are quite a bit different than IaaS or PaaS services because they are completely managed and maintained by the cloud provider. You don’t have the option of installing any of your own software with a SaaS service, so the deciding factor is related entirely to whether or not the provided-software meets your needs. The benefit of a SaaS service is that it largely removes the IT burden from your company, and it enables everyone in your company to access the software on multiple devices from just about anywhere Internet access is available. You also benefit from data backup that the cloud provider includes in their infrastructure. If you have a need to customize the application or have any control over its configuration, however, SaaS may not be a good choice for you.

The public cloud

The most common cloud model is the public cloud. In a public cloud model, you use shared infrastructure that is accessible on a public network. The network, storage, and VMs that your application uses are provided by a cloud provider and shared between all consumers of the public cloud. Microsoft Azure is an example of a public cloud.

The public cloud model is beneficial in that it makes it easy and fast to move to the cloud. Because the cloud provider already has the infrastructure in place and configured for you, all you have to do is decide on the type of cloud service you want and you’re off and running. You also benefit from the ability to scale quickly and efficiently because the cloud provider has resources already provisioned and ready for your use when needed.

As we discussed earlier, another advantage to the public cloud model is that you can control costs more efficiently because you only pay for the resources you are using. If you need to scale out to more VMs, the cloud provider has them available and waiting for you. You don’t have to maintain a pool of resources yourself. Instead, you take advantage of the resources the cloud provider has invested in.

While the flexibility and convenience of the public cloud is attractive, it comes with some disadvantages. First of all, you do give up some control of the infrastructure when using the public cloud. How much control depends on where you land on the cloud pyramid, but no matter what, the cloud provider is going to control some portion of your infrastructure.

There may also be security concerns with operating in the public cloud. The network involved in the public cloud is the public Internet, and it’s available to anyone with an Internet connection. That means you will need to have security measures in place to avoid unauthorized access to your application and data. Cloud providers realize this, and they provide security measure to help protect you, but those measures may not meet your security requirements.

Another disadvantage of the public cloud is that it locks you into the specific configuration defined by the cloud provider. For example, suppose you have an application that needs a large amount of disk storage, but you only need a single-CPU system to run it. In order to meet your disk space requirements, the cloud provider might require you to scale up to a high-powered, multi-CPU VM, thereby increasing your costs unnecessarily.

The private cloud

The private cloud model provides many of the attractive benefits of the cloud (things like easy scaling, and elasticity) in a private environment that is dedicated to a single company. A private cloud can be hosted in an on-premises environment, but it can also be hosted on a third-party hosting provider.

Two of the main reasons why companies choose a private cloud are: privacy and regulatory concerns. Unlike the public cloud, private clouds operate on a private network that is only accessible by a single organization. Businesses like banks and medical providers may have regulations in place that require certain data be inaccessible from the Internet, and in those situations, a private cloud might be a good choice. Another common consumer of private clouds is the cruise ship industry. Cruise ships operate in remote areas where Internet access isn’t available, but they still want to take advantage of the benefits of the cloud for day-to-day operations of complex ship systems.

There are some disadvantages to a private cloud. If you are hosting your private cloud on-premises, you will likely spend as much on IT as you would in a non-cloud environment. You will have to pay for hardware and virtualized systems for your cloud, and you’ll need IT staff who are capable of managing the software and infrastructure for your cloud.

Avoiding IT costs is one of the primary reasons that companies choose to use a third-party hosting provider for private clouds, but that choice also has some drawbacks. For example, once you offload management of your private cloud to a third-party, you lose control of important considerations, such as the security of your data. It’s often impossible to achieve full transparency when dealing with third-party providers, and you can’t always guarantee that data on your private cloud network will remain secured in a way that you require.

The hybrid cloud

As you might expect, hybrid clouds are a mixture of public and private clouds. In a hybrid cloud environment, you may have an application that is running within the public cloud, yet it accesses data that is securely stored on-premises. You might also have a scenario where your application and most of its resources are located on a private cloud, but you want to use services or infrastructure that are located in a public cloud. Indeed, the various scenarios that are suitable for a hybrid model are almost endless.

Hybrid cloud models are often a company’s first foray into the cloud. Many companies have legacy on-premises systems that are expensive to move to the cloud, yet you may want to take advantage of some of the benefits of the cloud. In such a scenario, a company might move only part of a particular system to the cloud, leaving the legacy system on-premises until a later time.

Not all companies adopting a hybrid cloud model are doing so because of legacy systems. In some situations, a company may want to maintain complete control over part of their infrastructure or data. They may decide to build out on-premises infrastructure in tandem with building their public cloud presence.

When companies adopt a hybrid model, they often require the capability of connecting the private, on-premise network with the public cloud network. Cloud providers offer many technologies to make that possible. In Microsoft Azure, Virtual Networks, Hybrid Connections, and Service Bus are just some examples of such technologies.

While it might not be immediately obvious, a hybrid cloud model comes with several challenges. First of all, application development teams will need to ensure that data shared between the public and private cloud is compatible. This might require some specialized development skills and complex troubleshooting. The networking complexities in a hybrid environment can also be quite challenging, especially because network infrastructure at third-party providers may introduce problems that are difficult to troubleshoot. Finally, spreading application resources between a public and a private cloud may cause application slowdowns due to the geographical distance between systems running the application and the data the application uses. All of these situations have to be carefully evaluated when deciding to use a hybrid cloud model.

In order to make hybrid cloud easier for its customers, Microsoft provides Azure Stack. Azure Stack is sold as a package, including software and validated hardware to run it. Azure Stack allows you to run Azure services on-premises, making it easy to then transfer applications to the cloud with a minimal amount of work. Because the hardware is part of Azure Stack and has been validated by Microsoft, you don’t have the burden of attempting to determine hardware needs in order to deploy Azure Stack, but you do have to manage the on-premises hardware.