Cloud Computing (Media Engineering Architecture & Deployment)

# Cloud Computing

Learn what cloud computing is and about the common service models available today.

This material is part of [architecture & deployment course](https://github.com/MediaComem/comem-archidep) for [Media Engineering](https://heig-vd.ch/formations/bachelor/filieres/ingenierie-des-medias).

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## Client-server model

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The [client-server model][client-server-model] is one of the main ways distributed and networked computer systems are organized today.
In this model, **servers** share their resources with **clients**, who **request a server's content or services**.

> The communication is not only one way.
> In modern web applications, servers may also **push data to their clients**.

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### Server-side

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The **server** is what we will focus on.

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### Types of servers

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A server can provide many different kinds of content or services:

* A [**file server**][file-server] provides shared disk access accessible over the network,
  to store files such as text, image, sound or video.
* A [**database server**][db-server] houses an application that provides database services to other computer programs.
* A [**web server**][web-server] can serve contents over the Internet.
* An [**application server**][app-server] provides an environment to run web applications.

These are just a few examples.
There are many [types of servers][server-types] depending on the scenario and the resources you want to provide.
One computer may fulfill one or several of these roles.

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### [Internet hosting][internet-hosting]

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Not every individual and organization has access to vast computer resources.
Some companies provide Internet servers that can be owned or leased by customers.

One common example is [web hosting][web-hosting],
where server space is provided to make websites accessible over the Internet.

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#### Types of web hosting

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[**Shared hosting**][shared-hosting]

Multiple websites (from a few to a few hundred) are placed on the same server
and **share a common pool of resources** (e.g. CPU, RAM).
This is the least expensive and least flexible model.

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[**Dedicated hosting**][dedicated-hosting]

Customers get full control over their own **physical server(s)**.
They are responsible for the security and maintenance of the server(s).
This offers the most flexibility and best performance.

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[**Virtual hosting**][virtual-hosting]

Using [virtualization][virtualization], physical server resources can be divided into **virtual servers**.
Customers gain full access to their own virtual space.

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### [Virtualization][virtualization]

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**Hardware virtualization** refers to the creation of a **virtual machine** that acts like a real computer with an operating system.

A **hypervisor** is installed on the **host machine**.
It virtualizes CPU, memory, network and storage.

A virtual machine, also called the **guest machine**,
runs another operating system **isolated** from the host machine.

For example, a computer running Microsoft Windows may host a virtual machine running an Ubuntu Linux operating system.
Ubuntu-based software can be run in the virtual machine.

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Popular virtualization solutions: [Linux KVM][kvm], [Parallels][parallels], [VirtualBox][virtualbox], [VMWare][vmware].

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#### Virtualized server architecture

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Using virtual machines provides several advantages:
applications can each run in an **isolated environment**
custom-tailored to their needs (operating system, libraries, etc).
**New virtual servers can be created in minutes.**
**Resource utilization is maximized** instead of hardware running idle.

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On the other hand, virtual machines require **additional management effort**
and their **performance is not as good** as dedicated servers.

But for many use cases **the benefits outweight the costs**,
which is why virtualization is heavily used in cloud computing.

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## Cloud computing

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### What is cloud computing?

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[Cloud computing][cloud] is nothing new.
It's simply a **pool of configurable computer system resources**.

These resources may be **servers**,
or **infrastructure** for those servers (e.g. network, storage),
or **applications** running on those servers (e.g. web applications).

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### Why use cloud computing?

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Cloud computing resources can be **rapidly provisioned** with **minimal management** effort, allowing great **economies of scale**.

Companies using cloud computing can **focus on their core business** instead of expending resources on computer infrastructure and maintenance.

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Pay-as-you-go models **minimize up-front computer infrastructure costs**.

They allow to more rapidly **adjust to fluctuating and unpredictable computing demands**.

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**Customization options are limited** since you do not have complete control over the infrastructure.

**Security and privacy** can be a concern depending on a business's legal requirements.

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### Deployment models

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Cloud infrastructure operated solely **for a single organization**,
managed and hosted internally or by a third party.

These clouds are very capital-intensive (they require physical space, hardware, etc)
but are usually more customizable and secure.

**Providers:** Microsoft, IBM, Dell, VMWare, HP, Cisco, Red Hat.

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Cloud services **open for public use**, provided over the Internet.

Infrastructure is often shared through virtualization.
Security guarantees are not as strong.
However, costs are low and the solution is highly flexible.

**Platforms:** [Amazon Web Services][aws], [Google Cloud Platform][google-cloud], [Microsoft Azure][azure].

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#### Other deployment models

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There are also **hybrid clouds** composed of two or more clouds bound together to benefit from the advantages of multiple deployment models.

For example, a platform may store sensitive data on a private cloud, but connect to other applications on a public cloud for greater flexibility.

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There also are a few [other deployment models][other-deployment-models],
for example **distributed clouds** where computing power can be provided by volunteers donating the idle processing resources of their computers.

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### Public clouds

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Most public **cloud computing providers** such as Amazon, Google and Microsoft **own and operate the infrastructure** at their data center(s),
and **provide cloud resources via the Internet**.

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For example, the Amazon Web Services cloud was [initially developed internally][aws-history] to support Amazon's retail trade.
As their computing needs grew, they felt the need to build a computing infrastructure that was **completely standardized and automated**,
and that would **rely extensively on web services** for storage and other computing needs.

As that infrastructure grew, Amazon started **selling access to some of their services**,
initially virtual servers, as well as a storage and a message queuing service.
Today Amazon is one of the largest and most popular cloud services provider.

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## Service models

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### What can I get?

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These are the main service models offered by cloud providers.

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### On premise data center

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As an introduction to cloud service models,
this is a representation of the various technological layers you need to put in place
to deploy web applications in a modern cloud infrastructure.

If you have your own data center, you need to install and configure all of these layers yourself.

As you will see, the various **cloud service models abstract away part or all** of these layers,
so that you don't have to worry about them.

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### Infrastructure as a Service (IaaS)

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[**IaaS**][iaas] provides fundamental IT infrastructure like **storage, networks and virtual machines** from the provider's data center(s).

The customer provides an **operating system image**, for example [Ubuntu][ubuntu],
which is run in a virtual machine by the provider.
The VM is the **unit of scale**, meaning that the customer pays per virtual machine, usually hourly.

The customer does not manage the physical infrastructure but has **complete control over the operating system** and can run **arbitrary software**.

Setting up the runtime environment (databases, web servers, monitoring, etc) for applications is the responsibility of the customer.

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#### How does IaaS work?

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System administrators connect to virtual machines run by the provider in their data center.
They have complete control over the operating system.
To run a website, they must set up the runtime environment themselves.

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### Platform as a Service (PaaS)

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[**PaaS**][paas] platforms provide a **managed runtime environment**
where customers can run their applications without having to maintain the associated infrastructure.

All the customer has to do is provide the **application or software**.
The platform will run it with the necessary additional components (e.g. database).
Pricing is per application, often hourly.

This is **quicker** because applications can be deployed with minimal configuration,
without the complexity of setting up the runtime.
More time can be spent on developing the application.

However PaaS is **less flexible** since control of the runtime environment and its configuration is limited.
It also tends to be more expensive at larger scales.

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#### How does PaaS work?

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Developers send an application, for example a Laravel site written in PHP, to the provider, typically via Git.
The managed runtime environment then detects the type of application and runs it, along with the necessary resources,
and serves it over the Internet.

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### Function as a Service (FaaS)

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[**FaaS**][faas] platforms store **individual functions** and run them in response to events.
Customers write simple functions which can access resources such as a database,
then define in which circumstances they are run (e.g. in response to client requests).

This model completely abstracts away both the infrastructure,
and the complexity of structuring an application.
The customer has no direct need to manage resources.

In contrast with IaaS and PaaS, nothing is kept running if nothing happens.
Functions are loaded and run as events occur.
**Pricing is based on execution time** (per millisecond) rather than application uptime.

The customer has little to no control over infrastructure, runtime and application layers.

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#### How does FaaS work?

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Developers write individual functions and publish them to the provider.
The platform provides various services to connect these functions together and to various resources for storage, communication, monitoring, etc.

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### Software as a Service (SaaS)

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[**SaaS**][saas] provides **on-demand** software over the Internet.

The software is **fully developed, managed and run by the provider**, so the customer has nothing to do except pay and use it.
Pricing is often per user and monthly.

This model offers the **least flexibility**, as the customer has no control over the operation or deployment of the software,
and limited control over its configuration.

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### Level of abstraction

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These models can be ordered by increasing level of abstraction,
from IaaS being the lowest level and most flexible service model,
to SaaS being the highest level and fastest-to-use service model.

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## Trends

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What's happening in the clouds?

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### Microservices

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There is a tendency in recent years to try to **decompose** monolithic applications into smaller, more flexible [microservices][microservices]
(a variant of service-oriented architecture).
The [Function-as-a-Service (FaaS)][faas] model is one more step in the same direction.

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#### [Microservice architecture][microservices-in-practice]

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Enterprise software often offers hundreds of functionalities piled into a single monolithic application.
The deployment, troubleshooting, scaling and upgrading of such monsters is a nightmare.

Isolating services allows development to be parallelized as teams can work autonomously on separate services,
or even individual functions.
It also faciliates [continous delivery][cd] as each component can be deployed independently.

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### Serverless computing

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The [Function-as-a-Service (FaaS)][faas] and [Mobile-Backend-as-a-Service (MBaaS)][mbaas]
are often considered to be part of the [**serverless computing**][serverless] model.

The name "serverless" does not mean that there is no server.
It just means that **the server is abstracted** and managed by the platform provider.

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* **Productivity**: the developer can focus on developing functions or business logic.
* **Cost-effective**: only the resources used are billed
  (whereas PaaS or IaaS resources may be underutilized).
* **Scalable**: the provider automatically scales resources to the demand.

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* **Greater latency**: infrequently-used code may be "shut down" when not in use.
* **Resource limits**: not suited to some workloads like high-performance computing.
* **Monitoring and debugging**: identifying performance problems may be more difficule than with traditional code.

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## References

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* [Advantages and Disadvantages of Virtual Server](https://www.esds.co.in/kb/advantages-and-disadvantages-of-virtual-server/)
* [Microservices in Practice][microservices-in-practice]

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## TODO

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* Containers, CaaS
* container pictures

[app-server]: https://en.wikipedia.org/wiki/Application_server
[aws]: https://aws.amazon.com/
[aws-history]: https://en.wikipedia.org/wiki/Amazon_Web_Services#History
[aws-lambda]: https://aws.amazon.com/lambda/
[azure]: https://azure.microsoft.com/
[azure-functions]: https://azure.microsoft.com/en-us/services/functions/
[cd]: https://en.wikipedia.org/wiki/Continuous_delivery
[client-server-model]: https://en.wikipedia.org/wiki/Client%E2%80%93server_model
[cloud]: https://en.wikipedia.org/wiki/Cloud_computing
[cloudboost]: https://www.cloudboost.io/
[cloud-foundry]: https://www.cloudfoundry.org/
[cloud-functions]: https://cloud.google.com/functions/
[db-server]: https://en.wikipedia.org/wiki/Database_server
[dedicated-hosting]: https://en.wikipedia.org/wiki/Dedicated_hosting_service
[dropbox]: https://www.dropbox.com/
[faas]: https://en.wikipedia.org/wiki/Function_as_a_service
[file-server]: https://en.wikipedia.org/wiki/File_server
[firebase]: https://firebase.google.com/
[gmail]: https://www.google.com/gmail/
[google-cloud]: https://cloud.google.com/
[heroku]: https://www.heroku.com/
[iaas]: https://en.wikipedia.org/wiki/Infrastructure_as_a_service
[internet-hosting]: https://en.wikipedia.org/wiki/Internet_hosting_service
[kvm]: https://www.linux-kvm.org/
[mbaas]: https://en.wikipedia.org/wiki/Mobile_backend_as_a_service
[microservices]: https://en.wikipedia.org/wiki/Microservices
[microservices-in-practice]: https://medium.com/microservices-in-practice/microservices-in-practice-7a3e85b6624c
[openshift]: https://www.openshift.com/
[other-deployment-models]: https://en.wikipedia.org/wiki/Cloud_computing#Others
[paas]: https://en.wikipedia.org/wiki/Platform_as_a_service
[parallels]: https://www.parallels.com
[saas]: https://en.wikipedia.org/wiki/Software_as_a_service
[server-types]: https://en.wikipedia.org/wiki/Server_(computing)#Purpose
[serverless]: https://en.wikipedia.org/wiki/Serverless_computing
[shared-hosting]: https://en.wikipedia.org/wiki/Shared_web_hosting_service
[slack]: https://slack.com/
[soa]: https://en.wikipedia.org/wiki/Service-oriented_architecture
[ubuntu]: https://www.ubuntu.com/
[virtualbox]: https://www.virtualbox.org
[virtual-hosting]: https://en.wikipedia.org/wiki/Virtual_private_server
[virtualization]: https://en.wikipedia.org/wiki/Virtualization
[vmware]: https://www.vmware.com
[web-hosting]: https://en.wikipedia.org/wiki/Web_hosting_service
[web-server]: https://en.wikipedia.org/wiki/Web_server