Cloud Provider Evaluation

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Learning Topic

Typical Cloud Architectures Single Server

The most basic use of the cloud is to provision a single virtual server, running your

application along with supporting service applications such as a database. Although a

single server is not much of an architecture, it can be used in a proof of concept project to

get your first experience with a particular cloud provider and see how easy and how fast

the provisioning process is.

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Single Server with Services

Instead of packing everything into a single server, a cloud consumer can advantage of

services available from the cloud provider. Here, we illustrate the use of a firewall service

and a database service. The provider will be responsible for provisioning the services and

keeping them running. The cloud consumer needs to populate and administer the data in

the database service. To accomplish that, the cloud consumer’s database administrator will

access the database using a virtual private network (VPN) connection over the Internet to

ensure security. The virtual server will run the business application and will connect to the

database service via a private network within the cloud provider’s data center.

Application with Security Zones and On-Premise IT Connectivity

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For large databases, proprietary data storage solutions, or databases unsupported by the

cloud provider, the data can be stored in a separate database virtual server. The cloud

provider will maintain the server but not the database. Because businesses value their

data as their most precious commodity, they will want to secure it by isolating it from

public Internet.

This can be accomplished by placing the database server in a separate private virtual local

area network (VLAN) than the application server, or a separate subnet in the same VLAN

as the application server. These VLANs (or subnets) will enforce security zones for their

devices. They will be made available to the outside by using network gateways: an

Internet gateway for the application server and a VPN gateway for the database server. In

addition, a network address translation (NAT) gateway between the security zones will

make sure that only trusted traffic can pass between them. These gateways are often

offered as a service by the cloud providers.

The VPN gateway for the database server can connect it to the on-premises enterprise

network of the cloud consumer, for taking on-premise backups, or integrating the cloud

solution with on-premises systems, enabling hybrid cloud deployments.

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Load Balancing, Auto-Scaling, Database Replication

User loads placed on web applications can differ significantly depending on the time of

the day, week, year, or any other circumstances. To remedy that, cloud providers offer

auto-scaling services. The cloud consumer can define an auto-scale group, specifying a

lower and upper limit on the number of servers in the group, the machine images from

which the servers are provisioned, and circumstances leading to up-and down-scaling in

the group. These can be based on calendar, or use of network bandwidth, CPU, or

memory on the servers.

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In order to split the incoming requests among the servers, a load-balancing service directs

the requests to the members of the group based on server use, or various queuing

algorithms (round-robin being the simplest).

With the database server, duplication requires keeping copies of the database in sync. A

preferred solution is to have one master database server, with a slave database server --

one using the database provider’s replication and synchronization capability. It ensures the

fault tolerance with respect to the database.

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Fault Tolerance and High Availability

The concept of replication can be extended to the application server, providing for a cloud

deployment that is fault-tolerant with respect to servers, and ensuring availability in

situations such as natural disasters or other circumstances that cause the whole data

center to go offline.

In addition, the application and databases can be replicated to different geographical

regions, ensuring fast access from remote geographical locations. And, replication can

help satisfy local government regulations regarding data privacy, which may require the

user’s data to reside within specific regions.

Fast Delivery of Static Content – Object Storage, Content Delivery Network

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While dynamic application data has to reside within the database server or service, static

content such as text, graphics, video, or audio files that don’t change that often can reside

in a slower but less expensive media. For that purpose, cloud providers offer object

storage, which can be thought of as an Internet-based file system, allowing for storage of

files organized into containers in a geographically distributed, replicated, secured storage.

While not at the speeds of local storage, object storage offers fault tolerance, resilience,

and virtually unlimited capacity at the cost of data consistency being “eventual” rather

that immediate.

Data stored in object storage can be often served by content delivery networks (CDNs) –

a service allowing for geographically distributing data and serving it from the closest

geographical location to the place from which the data request originates.

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Architecture Components Can Be Mixed and Matched

Bear in mind that cloud providers may allow some of the architectural components

illustrated here to be mixed and matched. For example, the auto-scale groups and

replicated databases could be placed in security zones, and VPN gateways could be linked

to different servers to corporate on-premises networks.

References

Open Data Center Alliance. (2014). Best practices: Architecting cloud-aware applications,

rev. 1.0. Retrieved from

https://www.opendatacenteralliance.org/docs/architecting_cloud_aware_applicati

ons.pdf

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