Home > Articles > Operating Systems, Server > Solaris

  • Print
  • + Share This
Like this article? We recommend

Like this article? We recommend

Applying Architectural Principles

Supporting key components of the sample ISP architectural model are architectural principles, as shown earlier and again in FIGURE 6. Architectural principles are major design considerations that help you qualify advantages and disadvantages of each design option, so that you arrive at a solution that best fits business requirements, functional requirements, and available technology.

FIGURE 6 ISP Architectural Model

We categorize architectural principles into eight areas: scalability, availability, reliability, manageability, adaptability, security, performance, and open system. Although there are other design principles you might need to use or consider, we focus on these as most critical.

Consider each of these principles (and any others that apply) when evaluating design issues and trade-offs for key components. For example, apply scalability to different layers within an architecture. You could address it at the network, system, and application layers. Failing to address scalability at each layer could result in nonoptimal scalability for an architecture.

Ultimately, some architectural principles may not apply to your design. However, it's important initially to consider them as part of the design process, especially for large-scale environments with higher levels of complexity. For example, if cost is a significant design constraint, then adding expensive layers of redundancy to enhance availability is most likely not applicable.

Scalability

Scalability is the ability to add additional resources, for example, routers, switches, servers, memory, disks, and CPUs to an architecture without redesigning it. A good design takes into account the need for scalability so that, within reason, as a business grows and user demand increases, new computing resources can be added on demand. Some customers have a clear idea of their plans for growth and indicate such at the beginning, while others may need you to suggest and build in scalability, based upon your interpretation of their current and future business requirements.

When you address scalability, we recommend using the following scaling models, depending upon which one is applicable to your design. These are simplified models that address scaling for both hardware and software at the same time during the architecture design process.

TABLE 1 Scaling Model for Servers

Scaling Model

Vertical

Horizontal

System Type:

Single Large System

Multiple Small Systems

Software Type:

Multithreaded applications

Single-threaded applications

To Scale:

Add CPU, memory, disk, and I/O

Add additional systems


Both models apply to key components. Each major component within an infrastructure, for example, network, system, application, storage, etc., has its own scaling model.

Vertical Scalability

Multithreaded applications are more complex in their scaling model. Typically, the first line of scaling within a single system for a multithreaded application within a single system is to achieve the maximum vertical scalability by adding more resources such as CPU, memory, and I/O. Vertical scaling is appropriate for applications that scale well within a single large server, such as database servers.

TIP

Scale multithreaded applications vertically first. When maximum vertical scaling is achieved, scale the same applications using horizontal scaling techniques, for example, running the applications on multiple boxes behind a load balancer.

Horizontal Scalability

For single-threaded applications, the model for scaling is horizontal. In this model, a vertical scaling limitation of the server is replaced with a much more scalable load distribution paradigm. This technique is deployed at a system level by adding more servers to increase scalability.

TIP

Unlike multithreaded applications, single-threaded applications do not achieve optimal benefits from vertical scaling. For example, adding more memory benefits single-threaded applications; however, adding another CPU does not. Scaling horizontally can be done by running multiple instances on multiple boxes behind a load balancer.

In contrast to availability, which is designed for failover, the purpose of multiple system redundancy in scalability is to provide a model for adding resources to increase capacity.

Availability

Availability has many definitions within Internet architectures. In this book, it means that resources and access to those resources are available upon request. Availability design is predicated on the removal of any single point-of-failure within an architecture to ensure a desired level of uptime. This uptime is usually expressed in percentages and often referred as the "number of 9s." For example, most mission critical systems have a desired uptime of "five 9s," meaning that the system is available 99.999 percent of the time.

TABLE 2 Availability Levels

Uptime Percentage

Nines

Allowable Downtime Per Month

99.9999

6

0.043 minute

99.999

5

0.43 minute

99.99

4

4.30 minutes

99.9

3

43 minutes

99

2

7.2 hours


We determined allowable downtime by using the following formula:1

Availability= MTBF
MTBF + MTTR

where MTBF is mean time between failure and MTTR is mean time to repair.

For marketing reasons, many ISPs calculate the level of availability over a 12-month period instead of monthly. (This practice yields an overall higher average level of availability than calculating it monthly, because monthly calculations fluctuate from month to month.)

We calculate the availability monthly because system administrators typically perform maintenance monthly; therefore, monthly calculations are more beneficial for determining allowable downtime to perform maintenance and upgrades. This practice is fairly universal for system administrators of ISPs. Other reasons for calculating it on a monthly basis:

  • Revenue, usage, stats, spending, etc. are done monthly.

  • Waiting for one year to find out the level of availability is unrealistic.

A primary attribute of availability design is redundant hardware/software within the architecture, such as network, server, application, and storage.

TIP

Design in such a way that if a component fails, it does not cause the entire architecture to fail. To achieve this design objective, design using a modular approach, allowing components to be replaced at any time without affecting the availability of the system.

The four layers, covered in the following paragraphs, are as follows:

  • Network layer
  • System layer
  • Application layer
  • Data layer

Network Layer

At the network layer, availability can be achieved with redundant physical links to the Internet. This redundancy ensures that if there is a link failure, for example, due to hardware failure, access is still available via a surviving link. In addition, redundant network components such as routers, switches, load balancers, and firewalls are necessary to ensure access availability in the event of hardware failure. To enhance reliability at the network layer, remove all single points-of-failure from the network.

NOTE

For the Solaris_ Operating Environment (Solaris OE), IP multi-pathing (IPMP) can be used to achieve redundant network connections from the same server to multiple switches.

System Layer

At the system layer, availability is achieved with redundant servers in stand-alone or cluster configurations.

For front-end servers such as those deployed in web farms, you can use load balancers to ensure availability in the event that one or more servers fail to respond to service requests.

In a cluster environment, two or more servers are configured to provide high availability. The number of nodes configured in a cluster is dependent upon the software and hardware. If one server fails, one of the surviving servers takes over and responds to service requests.

A fundamental difference between stand-alone servers and clustered servers is the ability to maintain session states. If a stand-alone server fails while a session is active, the connection has to be reestablished from the client. However, if a clustered server fails, the session state and connection is maintained by a standby server.

NOTE

The cost of redundant servers and software licensing is extremely expensive for small- to mid-size ISPs. However, without it, ISPs may lose subscribers and revenue to competing ISPs because of subscriber dissatisfaction from service interruptions. Subscriber expectations for availability and reliability are usually high, and many competitors already offer high availability and reliability.

Application Layer

At the application layer, availability can be achieved with clustering and high availability software. You can configure applications with clusters or high availability to enhance availability in the event of service failure. Service failure and restart can be automatically invoked through service failure detection and monitoring. Also, you can enhance availability at the application layer by using a load balancer with multiple servers.

Data Layer

At the data layer, availability can be achieved with redundant storage arrays coupled with logical volumes. Redundant storage arrays allow data to be accessible in the event of a controller or storage array failure. Logical volumes and RAID (redundant array of independent disks) ensure data is accessible in the event of disk failure.

At the data layer, RAID 0+1 (stripping and mirroring) or RAID 5 (stripping with parity) achieves availability and reliability in case of disk failure. RAID 0+1 is a more expensive solution because twice the hardware (storage arrays and disks) is needed. However, the advantage is that no performance degradation occurs due to a disk failure. RAID 5 can have performance degradation if a disk fails, because data has to be rebuilt from parity.

Reliability

Reliability is best defined from the perspective of end users. Users want network services and servers to be available when they access them. Reliability for them is consistency of service uptime and availability. To users, a system is reliable when they do not frequently encounter busy signals on their modems, network connection error messages, etc.

From an architect's perspective, reliability is uptime and service response time for users, so that a system is available when users access services.

For businesses today, especially service providers, reliability of service has implications beyond customer satisfaction. Because service providers establish and maintain their reputations based on availability and reliability of their services, many of them require carrier-class grade high availability and reliability.

TIP

Reliability depends upon and is affected by the design for availability; therefore, your design for an ISP architecture should balance a customer's requirements for both availability and reliability, within any constraints imposed by customer or technology.

Dependent upon availability design, reliability is increased through an infrastructure based on redundant servers. Functionally componentized architecture results in more intrinsic redundancy and fewer inherent single points-of-failure. Furthermore, any damage to an individual service is unlikely to impact other services.

The constructs of redundancy are useful in achieving many aspects of reliability, scalability, and availability.

Manageability

Manageability addresses how an infrastructure can be managed during its life cycle. The key to manageability is to keep an architecture design simple, yet effective. Meet all functional and business requirements without adding complexity. If a design is too complex and difficult to manage, there is more likelihood for operation and management failure, and troubleshooting becomes more difficult and time consuming. Also consider management tools, management plans, and methods of monitoring services. Ensure that devices and components that need to be monitored are managed. If a system goes down and there is nothing monitoring the device or component causing the outage, customer satisfaction and subscriber satisfaction are at risk, in addition to associated costs and potential loss of revenue.

Adaptability

For any architecture, change during a life cycle is inevitable. An architecture must be adaptable enough to accommodate growth and changes in technology, business, and user needs. Within the customer's financial constraints and growth plans, design an architecture that allows for adaptability.

Modular architectures inherently support flexibility in two ways: individual components are themselves easily augmented, and, because components are independent, new components can be added without disturbing or revamping other components within an architecture.

Security

From a larger perspective, security is a combination of processes, products, and people. Security is achieved by establishing effective policies and implementing procedures that enforce policies. Security policies are useless without control over who has access to and can affect security on servers and services. Securing access requires establishing an appropriate authentication regime.

From an architecture perspective, security is access to network, system, and data resources.

  • At the network layer, security can be achieved with an access control list (ACL) on routers, packet filters, firewalls, and network-based intrusion detection systems (IDS).

  • At the system layer, security can be achieved with system hardening, access permission, host-based IDSs, scanners, and file checkers.

  • At the data layer, security can be achieved with authentication and authorization.

Functional decomposition (separating functional components) contributes to security by making it easy to build security around different components. In addition, if one component is compromised, the security breach may be more easily contained.

Adapting to evolving threats is a never-ending cycle of processes. The strategy of responding to security threats has to evolve as potential intruders gain knowledge and discover new attack techniques.

We recommend designing security strategies with great flexibility in approaches to provide the best security against present and future threats.

Performance

Although performance has multiple definitions, in this book we relate it to the "expected" response time after a user requests a service. Depending upon an ISP's requirements, response time may be critical or noncritical, and these distinctions may be further refined by service type.

Individual services use system resources, for example, memory, CPU, and I/O, in different ways. A modular architecture provides the ability to independently monitor and tune each service.

The causes of slow response times are many. For example, some common causes are network latency, server degradation, and application responsiveness. Degradation at any of these layers can result in poor overall performance.

A system is easier to tune when it is running only a few applications. When many applications are running on a system, they must share resources, and tuning becomes complicated and challenging.

TIP

Two products available from Sun are useful in managing resources: Solaris Resource Manager and Solaris Bandwidth Manager. The Solaris Resource Manager manages resources for users, groups, and enterprise applications. The Solaris Bandwidth Manager controls bandwidth allocated to applications, users, and organizations.

Open System

Ideally, design using an open system approach so that an architecture is not dependent upon a single hardware or software vendor. An architecture is less flexible when built upon proprietary specifications. Building upon a set of open system standards that are accepted by a recognized consortium provides greater flexibility for business changes and growth, such as adding users and services and integrating new technology.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020