I have heard this more than once.

"Nobody is using the private cloud now!"

May be you've heard it too.

But the reality is different.

40% of the respondents in the CNCF annual survey said they were using on-premise private cloud.

So, private cloud is not a thing in the bygone era.

Who is using private cloud

Hot new startups are not using the private cloud. Perhaps that's the reason for the misconception that private cloud is dead and gone.

Those who are using private cloud are not the old-world companies either. 37 Signals, the creators of Basecamp and Hey have moved everything to private cloud some time back.

If you are to look closely at the businesses using private cloud, you'll find out that they are established enterprises with a steady cash flow. Some of them like 37 Signals, started their journey in the public cloud and later moved back to private cloud. But many other like banks, telecom service providers, hospitals, etc., have started their cloudification journey with private cloud.

Why use private cloud

In the private cloud, you own the hardware and software. You decide which hardware to buy, where you install the hardware, and which software to use. So, you have total control over your cloud infrastructure.

This ownership and control yield a few unique advantages to the private cloud users.

1. Cost:
   Public cloud, though it requires zero investments at the start, becomes expensive as you scale up. And at a certain point, the recurring cost of the public cloud can become intolerable.
   
   Also, with scale, you get the ability to hire experts and bargain with hardware and software suppliers, which makes private cloud even more attractive. So, organizations with very large computing capacity can gain a significant cost benefit by opting in for the private cloud.

2. Latency:
   You can design the private cloud with guaranteed latency by installing hardware in specific geographic locations - closer to your users. You cannot do so with public cloud. So companies like stock exchanges and hospitals use private cloud for their latency-critical applications.

3. Bandwidth:
   If you are handling network traffic in Terabits per second, like telecom companies are doing, public cloud is not an option for you. The networking cost of plumbing this huge volume of traffic to public cloud data centers, easily puts any public cloud business case out of question for these companies. So, telecom service providers have become a big fan of the private cloud.

4. Digital sovereignty:
   Due to compliance requirements, some businesses want to store PII (Personally Identifiable Information) within their physical premises or within a specific geographical boundary. So these businesses host their software applications in the private cloud.

Private cloud is more work than public cloud.

You must attend to hardware faults and replace faulty components. You must patch your cloud software and operating systems to keep them up to date. You must make sure you have adequate networking bandwidth. And you will need many more chores to keep your private cloud up and running.

Yet, the unique advantages we mentioned above can justify this overhead for some organization. So, we will not see private cloud going away anytime soon.

On-premise private cloud vs off-premises private cloud

Not everyone is using the private cloud in the same way. Organizations adopt different approaches and deployment models for their public clouds.

One main difference is where you install the computing hardware.

On-premises private cloud

Computing infrastructure that makes up a cloud can only line in strictly controlled environment. This environment is facilitated inside a data center.

A data center needs civil infrastructure that can support the loading requirements of the computing equipment which is way more than the loading capacity in an average office building. Also a data center needs cooling, power with back up, humidity control, dust proofing, and a lot of other nuances that's not available in ordinary civil structures used for an office or a school.

Building a data center is a big investment. Once built, you also need staff to maintain it.

If you can afford your own data center, you can build a private cloud on your premises.

Off-premises private cloud

Having an on-premises data center is not a must for a private cloud. You can build a private cloud by installing your computing hardware in rented racks inside a data center owned by another company.

Often, telecom companies are in the business of renting data center racks. But there can be other players too.

They provide the rack spaces in their data centers on monthly or annual rental. They also offer other value adding services like Internet bandwidth, firewall services, hardware management, that you can utilize for operating your private cloud.

You can rent some racks, install your computing hardware and build a private cloud if you do not want to or cannot afford to build a data center on your own.

This type of private cloud is also called a managed private cloud.

Virtualized vs containerized private cloud

Just a bunch of computers (aka bare-metal servers) installed at a data center doesn't make up a cloud. You need a software stack on top, to make those computing resources available to the end users - the software developers.

According to that software stack there are two types of clouds; virtualized and containerized.

Virtualized private cloud

In a virtualized private cloud, you have a virtualization software stack installed on the bare-metal servers.

This software stack allows you to create virtual servers for users (developers) to run their software applications.

For the virtualization software stack, you have three main options.

1. OpenStack
   OpenStack is an open-source cloud software platform with a large number of components that implement different cloud services such as networking, storage, orchestration, etc. You can install OpenStack on a pool of bare-metal server and use OpenStack CLI or GUI to manage the entire lifecycle of virtual servers.

2. VMware
   VMware is a proprietary cloud platform that is offered in several different licensing schemes. Similar to OpenStack, it lets you create virtual servers.

3. KVM
   KVM is the hypervisor used in OpenStack. The hypervisor is responsible for running a virtual machine on a bare-metal server. In addition to KVM, OpenStack includes a plethora of other components for automating virtual machine management across hundreds of servers.
   
   This scalability comes with an operational overhead as you need to manage the lifecycle of OpenStack components. If you do not want to scale your private cloud to hundreds of servers, the operational overhead of OpenStack would be just a burden without any value addition.
   In that case, you can install KVM alone on the bare-metal servers and provision the virtual servers manually.

Containerized private cloud

A containerized private cloud allows users to run containerized applications.

Kubernetes is the most popular software platform used in containerized private clouds. You can deploy Kubernetes on either bare-metal servers or on virtual servers created via OpenStack or VMware.

Running Kubernetes on virtual servers allows you to maintain your cloud dual-stack - you can offer your users to consume the cloud either as virtual servers or as containers. But, you need to maintain the virtualization stack in addition to Kubernetes. And it can be an operational burden.

You can eliminate this operational burden by running Kubernetes directly on bare-metal servers. The downside is you loose some flexibility.

When you deploy Kubernetes on top of a virtualization layer, you can easily share your capacity across multiple Kubernetes clusters. Also, restoring a failed Kubernetes node is easy. You just need to provision a new virtual server.

You will see both of these approaches across different organizations using private clouds.

Kubernetes in the private cloud: Self-managed vs managed

Kubernetes in the private cloud can be either self-managed or managed by a vendor.

Self-managed Kubernetes

Kubernetes is an open-source project.

If you have sufficient expertise, you can install and managed Kubernetes in your private cloud on your own. You don't have to pay any licenses. But, if something goes wrong, you would be on your own to fix it.

Managed Kubernetes

If you don't like to be bothered with operating Kubernetes on your own, you can get a bundled Kubernetes distribution from a supplier.

VMware Tanzu, RedHat OpenShift, Canonical charmed Kubernetes are three such Kubernetes distributions. Recently, the big cloud providers have also released their Kubernetes distributions that can be installed on private cloud.

DevOps in the private cloud vs public cloud

Private clouds lack some key characteristics of the public cloud.

In the public cloud, computing resources are available on-demand. It allows you to automate resource management lifecycle easily.

In the private cloud, you need to look at the resource management from a different perspective.

We'll dive into it in the next week's post.