What is High Availability? A Tutorial | Liquid Web

High Availability

High availability is the description of a system designed to be fault-tolerant, highly dependable, operates continuously without intervention, or having a single point of failure. These systems are highly sought after to increase the availability and uptime required to keep an infrastructure running without issue. The following characteristics define a High Availability system.

High Availability Clustering

High-availability server clusters (aka HA Clusters) is defined as a group of servers which support applications or services that can be utilized reliably with a minimal amount of downtime. These server clusters function using a type of specialized software that utilizes redundancy to achieve mission-critical levels of five9’s uptime. Currently, approximately 60% of businesses require five9’s or greater to provide vital services for their businesses.

High availability software capitalizes on the redundant software installed on multiple systems by grouping or clustering together a group of servers focusing on a common goal in case components fail. Without this form of clustering, if the application or website crashes, the service will not be available until the servers are repaired. HA clustering addresses these situations by detecting the faults and quickly restarting or replacing the server or service or server with a new process that does not require human intervention. This is defined as a “failover” model.

The illustration below demonstrates a simple two node high availability cluster.

2nodeHAcluster

High Availability clusters are often used for mission-critical databases, data sharing, applications, and e-commerce websites spread over a network. High Availability implementations build redundancy within a cluster to remove any one single point of failure, including across multiple network connections and data storage, which can be connected redundantly via geographically diverse storage area networks.

High Availability clustered servers usually use a replication methodology called Heartbeat that is used to monitor each node’s status and health within the cluster over a private network connection. One critical circumstance all clustering software must be able to address is called split-brain, which occurs when all private internal links go down simultaneously, but the nodes in the cluster continue to run. If this occurs, every node within the cluster may incorrectly determine that all the other nodes have gone down and attempt to start services that other nodes may still be running. This condition of duplicate instances running similar services, which could cause data corruption on the system.

ha.cluster

A typical version of high availability software provides attributes that include both hardware and software redundancy. These features include:

  • The automatic detection and discovery of hardware and software components.
  • Autonomous assignment of both active and contingent roles to new elements.
  • Detection of failed software services, hardware components, and other system constructs.
  • Monitoring and notification of redundant components and when they need to be activated.
  • Ability to scale the cluster to accommodate the required changes without external intervention.

Fault tolerance

fault.tolerance

Fault tolerance is defined as the ability for a system’s infrastructure to foresee and withstand errors and provide an automatic response to those issues if encountered. The primary quality of these systems is advanced design factors, which can be called upon should a problem occur. Being able to configure an infrastructure that envisions every possible solution is a considerable task that involves the knowledge and experience to counter the multiple concerns before they occur. System architects who design such frameworks will have the methodologies which envision the means to alleviate these problems in advance, and the ability to implement these frameworks.

The following redundancy methodologies are available and should be reviewed during the initial stages of design and implementation.

  • N + 1 Model – This concept infers the sum of equipment needed (which we will refer to as ‘N’) to keep the entire framework up and running, with an additional independent component backup for each of the ‘N’ components in case of failure.
  • N + 2 Model – Similar to the N + 1 model but with an additional layer of protection if two components should fail.
  • 2N Model – This modality has a dual redundant backup for each element to ensure the system’s framework is fully functional.
  • 2N + 1 Model – Again, this model is similar to the 2N model but with a supplemental component to add a tertiary layer of protection to the system’s framework.

As models progress from Nx to 2Nx, the cost factor also increases exponentially as for truly redundant systems that require uptime. These modalities are critical for stability and availability.

Dependability and Reliability

One of the central tenants of a high availability system is uptime. Uptime is of premier importance, especially if the purpose of a system is to provide an essential service like the 911 systems that respond to emergent situations. In business, having a high availability system is required to ensure a vital service remains online. One example would be an ISP or other service that cannot tolerate a loss of function. These systems must be designed with high availability and fault tolerance to ensure reliability and availability while minimizing downtime.

Orchestrated Error Handling

Should an error occur, the system will adapt and compensate for the issue while remaining up and online. Building this type of system requires forethought and planning for the unexpected. Being able to foresee the problems in advance, and planning for their resolution is one of the main qualities of a high availability system.

Scalability

Should the system encounter an issue like a traffic spike or an increase in resource usage, the system’s ability to scale to meet those needs should be automatic and immediate. Building features like these into the system will provide the system’s ability to respond quickly to any change in the systemic functionality of the architectures processes.

Availability & Five 9’s Uptime

Five 9’s is the industry standard of measure of uptime. This measurement can be related to the system itself, the system processes within a framework, or the program operating inside an infrastructure. This estimation is often related to the program being delivered to clients in the form or a website or web application. A systems Availability can be measured as the percentage of time that systems are available by using this equation: x = (n – y) * 100/n. This formula denotes that where “n” is the total amount of minutes within a calendar month, and “y” is the amount of minutes that service is inaccessible within a calendar month. The table below outlines downtime related to the percentage of “9’s” represented.

**Availability %**90%

(“1 Nine“)99%

(“2 Nines“)99.9%

(“3 Nines“)99.99%

(“4 Nines“)99.999%

(“5 Nines“)Downtime/Year36.53 days3.65 days8.77 hours52.60 minutes5.26 minutes

As we can see, the higher the number of “9’s”, the more uptime is provided. A high availability system’s goal is to achieve a minimal amount of potential downtime to ensure the system is always available to provide the designated services.

Heartbeat

One of the main High Availability components is called Heartbeat. Heartbeat is a daemon which works with a cluster management software like Pacemaker that is designed specifically for high-availability clustering resource management. Its most important characteristics are:

  • No specific or fixed maximum number of nodes – Heartbeat can be used to build large clusters as well as elementary ones.
  • Resource monitoring: resources can be automatically restarted or moved to another node on failure.
  • A fencing mechanism needed to remove failed nodes from the cluster.
  • A refined policy-based resource management, resource inter-dependencies, and constraints.
  • A time-based rule set to allow for different policies depending on a defined timeframe.
  • A group of resource scripts (for software like Apache, DB2, Oracle, PostgreSQL, etc.) included more granular management.
  • A GUI for configuring, controlling and monitoring resources and nodes.

Cluster Architecture

**Engineered Availability **

The first segment of a highly available system is the clearly designed utilization of clustered application servers that are engineered in advance to distribute load amongst the whole cluster, which includes the ability to failover to a secondary and possibly a tertiary system.

The second division includes the need for database scalability. This entails the requirement of scaling, either horizontally or vertically, using multiple master replication, and a load balancer to improve the stability and uptime of the database.

ha cluster

#tutorials #2nx models #architecture #autonomous #availability #backups #best practice #clustering #deployment #design #disaster recovery #downtime #engineered #fault tolerance #ha cluster #heartbeat #high availability #infrastructure #monitoring #node #nx models #orchestrated #pacemaker #redundancy #reliability #replication #scalability #single point of failure #split brain #system #testing #uptime

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What is High Availability? A Tutorial | Liquid Web

What is High Availability? A Tutorial | Liquid Web

High Availability

High availability is the description of a system designed to be fault-tolerant, highly dependable, operates continuously without intervention, or having a single point of failure. These systems are highly sought after to increase the availability and uptime required to keep an infrastructure running without issue. The following characteristics define a High Availability system.

High Availability Clustering

High-availability server clusters (aka HA Clusters) is defined as a group of servers which support applications or services that can be utilized reliably with a minimal amount of downtime. These server clusters function using a type of specialized software that utilizes redundancy to achieve mission-critical levels of five9’s uptime. Currently, approximately 60% of businesses require five9’s or greater to provide vital services for their businesses.

High availability software capitalizes on the redundant software installed on multiple systems by grouping or clustering together a group of servers focusing on a common goal in case components fail. Without this form of clustering, if the application or website crashes, the service will not be available until the servers are repaired. HA clustering addresses these situations by detecting the faults and quickly restarting or replacing the server or service or server with a new process that does not require human intervention. This is defined as a “failover” model.

The illustration below demonstrates a simple two node high availability cluster.

2nodeHAcluster

High Availability clusters are often used for mission-critical databases, data sharing, applications, and e-commerce websites spread over a network. High Availability implementations build redundancy within a cluster to remove any one single point of failure, including across multiple network connections and data storage, which can be connected redundantly via geographically diverse storage area networks.

High Availability clustered servers usually use a replication methodology called Heartbeat that is used to monitor each node’s status and health within the cluster over a private network connection. One critical circumstance all clustering software must be able to address is called split-brain, which occurs when all private internal links go down simultaneously, but the nodes in the cluster continue to run. If this occurs, every node within the cluster may incorrectly determine that all the other nodes have gone down and attempt to start services that other nodes may still be running. This condition of duplicate instances running similar services, which could cause data corruption on the system.

ha.cluster

A typical version of high availability software provides attributes that include both hardware and software redundancy. These features include:

  • The automatic detection and discovery of hardware and software components.
  • Autonomous assignment of both active and contingent roles to new elements.
  • Detection of failed software services, hardware components, and other system constructs.
  • Monitoring and notification of redundant components and when they need to be activated.
  • Ability to scale the cluster to accommodate the required changes without external intervention.

Fault tolerance

fault.tolerance

Fault tolerance is defined as the ability for a system’s infrastructure to foresee and withstand errors and provide an automatic response to those issues if encountered. The primary quality of these systems is advanced design factors, which can be called upon should a problem occur. Being able to configure an infrastructure that envisions every possible solution is a considerable task that involves the knowledge and experience to counter the multiple concerns before they occur. System architects who design such frameworks will have the methodologies which envision the means to alleviate these problems in advance, and the ability to implement these frameworks.

The following redundancy methodologies are available and should be reviewed during the initial stages of design and implementation.

  • N + 1 Model – This concept infers the sum of equipment needed (which we will refer to as ‘N’) to keep the entire framework up and running, with an additional independent component backup for each of the ‘N’ components in case of failure.
  • N + 2 Model – Similar to the N + 1 model but with an additional layer of protection if two components should fail.
  • 2N Model – This modality has a dual redundant backup for each element to ensure the system’s framework is fully functional.
  • 2N + 1 Model – Again, this model is similar to the 2N model but with a supplemental component to add a tertiary layer of protection to the system’s framework.

As models progress from Nx to 2Nx, the cost factor also increases exponentially as for truly redundant systems that require uptime. These modalities are critical for stability and availability.

Dependability and Reliability

One of the central tenants of a high availability system is uptime. Uptime is of premier importance, especially if the purpose of a system is to provide an essential service like the 911 systems that respond to emergent situations. In business, having a high availability system is required to ensure a vital service remains online. One example would be an ISP or other service that cannot tolerate a loss of function. These systems must be designed with high availability and fault tolerance to ensure reliability and availability while minimizing downtime.

Orchestrated Error Handling

Should an error occur, the system will adapt and compensate for the issue while remaining up and online. Building this type of system requires forethought and planning for the unexpected. Being able to foresee the problems in advance, and planning for their resolution is one of the main qualities of a high availability system.

Scalability

Should the system encounter an issue like a traffic spike or an increase in resource usage, the system’s ability to scale to meet those needs should be automatic and immediate. Building features like these into the system will provide the system’s ability to respond quickly to any change in the systemic functionality of the architectures processes.

Availability & Five 9’s Uptime

Five 9’s is the industry standard of measure of uptime. This measurement can be related to the system itself, the system processes within a framework, or the program operating inside an infrastructure. This estimation is often related to the program being delivered to clients in the form or a website or web application. A systems Availability can be measured as the percentage of time that systems are available by using this equation: x = (n – y) * 100/n. This formula denotes that where “n” is the total amount of minutes within a calendar month, and “y” is the amount of minutes that service is inaccessible within a calendar month. The table below outlines downtime related to the percentage of “9’s” represented.

**Availability %**90%

(“1 Nine“)99%

(“2 Nines“)99.9%

(“3 Nines“)99.99%

(“4 Nines“)99.999%

(“5 Nines“)Downtime/Year36.53 days3.65 days8.77 hours52.60 minutes5.26 minutes

As we can see, the higher the number of “9’s”, the more uptime is provided. A high availability system’s goal is to achieve a minimal amount of potential downtime to ensure the system is always available to provide the designated services.

Heartbeat

One of the main High Availability components is called Heartbeat. Heartbeat is a daemon which works with a cluster management software like Pacemaker that is designed specifically for high-availability clustering resource management. Its most important characteristics are:

  • No specific or fixed maximum number of nodes – Heartbeat can be used to build large clusters as well as elementary ones.
  • Resource monitoring: resources can be automatically restarted or moved to another node on failure.
  • A fencing mechanism needed to remove failed nodes from the cluster.
  • A refined policy-based resource management, resource inter-dependencies, and constraints.
  • A time-based rule set to allow for different policies depending on a defined timeframe.
  • A group of resource scripts (for software like Apache, DB2, Oracle, PostgreSQL, etc.) included more granular management.
  • A GUI for configuring, controlling and monitoring resources and nodes.

Cluster Architecture

**Engineered Availability **

The first segment of a highly available system is the clearly designed utilization of clustered application servers that are engineered in advance to distribute load amongst the whole cluster, which includes the ability to failover to a secondary and possibly a tertiary system.

The second division includes the need for database scalability. This entails the requirement of scaling, either horizontally or vertically, using multiple master replication, and a load balancer to improve the stability and uptime of the database.

ha cluster

#tutorials #2nx models #architecture #autonomous #availability #backups #best practice #clustering #deployment #design #disaster recovery #downtime #engineered #fault tolerance #ha cluster #heartbeat #high availability #infrastructure #monitoring #node #nx models #orchestrated #pacemaker #redundancy #reliability #replication #scalability #single point of failure #split brain #system #testing #uptime

Evolution in Web Design: A Case Study of 25 Years - Prismetric

The term web design simply encompasses a design process related to the front-end design of website that includes writing mark-up. Creative web design has a considerable impact on your perceived business credibility and quality. It taps onto the broader scopes of web development services.

Web designing is identified as a critical factor for the success of websites and eCommerce. The internet has completely changed the way businesses and brands operate. Web design and web development go hand-in-hand and the need for a professional web design and development company, offering a blend of creative designs and user-centric elements at an affordable rate, is growing at a significant rate.

In this blog, we have focused on the different areas of designing a website that covers all the trends, tools, and techniques coming up with time.

Web design
In 2020 itself, the number of smartphone users across the globe stands at 6.95 billion, with experts suggesting a high rise of 17.75 billion by 2024. On the other hand, the percentage of Gen Z web and internet users worldwide is up to 98%. This is not just a huge market but a ginormous one to boost your business and grow your presence online.

Web Design History
At a huge particle physics laboratory, CERN in Switzerland, the son of computer scientist Barner Lee published the first-ever website on August 6, 1991. He is not only the first web designer but also the creator of HTML (HyperText Markup Language). The worldwide web persisted and after two years, the world’s first search engine was born. This was just the beginning.

Evolution of Web Design over the years
With the release of the Internet web browser and Windows 95 in 1995, most trading companies at that time saw innumerable possibilities of instant worldwide information and public sharing of websites to increase their sales. This led to the prospect of eCommerce and worldwide group communications.

The next few years saw a soaring launch of the now-so-famous websites such as Yahoo, Amazon, eBay, Google, and substantially more. In 2004, by the time Facebook was launched, there were more than 50 million websites online.

Then came the era of Google, the ruler of all search engines introducing us to search engine optimization (SEO) and businesses sought their ways to improve their ranks. The world turned more towards mobile web experiences and responsive mobile-friendly web designs became requisite.

Let’s take a deep look at the evolution of illustrious brands to have a profound understanding of web design.

Here is a retrospection of a few widely acclaimed brands over the years.

Netflix
From a simple idea of renting DVDs online to a multi-billion-dollar business, saying that Netflix has come a long way is an understatement. A company that has sent shockwaves across Hollywood in the form of content delivery. Abundantly, Netflix (NFLX) is responsible for the rise in streaming services across 190 countries and meaningful changes in the entertainment industry.

1997-2000

The idea of Netflix was born when Reed Hastings and Marc Randolph decided to rent DVDs by mail. With 925 titles and a pay-per-rental model, Netflix.com debuts the first DVD rental and sales site with all novel features. It offered unlimited rentals without due dates or monthly rental limitations with a personalized movie recommendation system.

Netflix 1997-2000

2001-2005

Announcing its initial public offering (IPO) under the NASDAQ ticker NFLX, Netflix reached over 1 million subscribers in the United States by introducing a profile feature in their influential website design along with a free trial allowing members to create lists and rate their favorite movies. The user experience was quite engaging with the categorization of content, recommendations based on history, search engine, and a queue of movies to watch.

Netflix 2001-2005 -2003

2006-2010

They then unleashed streaming and partnering with electronic brands such as blu-ray, Xbox, and set-top boxes so that users can watch series and films straight away. Later in 2010, they also launched their sophisticated website on mobile devices with its iconic red and black themed background.

Netflix 2006-2010 -2007

2011-2015

In 2013, an eye-tracking test revealed that the users didn’t focus on the details of the movie or show in the existing interface and were perplexed with the flow of information. Hence, the professional web designers simply shifted the text from the right side to the top of the screen. With Daredevil, an audio description feature was also launched for the visually impaired ones.

Netflix 2011-2015

2016-2020

These years, Netflix came with a plethora of new features for their modern website design such as AutoPay, snippets of trailers, recommendations categorized by genre, percentage based on user experience, upcoming shows, top 10 lists, etc. These web application features yielded better results in visual hierarchy and flow of information across the website.

Netflix 2016-2020

2021

With a sleek logo in their iconic red N, timeless black background with a ‘Watch anywhere, Cancel anytime’ the color, the combination, the statement, and the leading ott platform for top video streaming service Netflix has overgrown into a revolutionary lifestyle of Netflix and Chill.

Netflix 2021

Contunue to read: Evolution in Web Design: A Case Study of 25 Years

#web #web-design #web-design-development #web-design-case-study #web-design-history #web-development

Willie  Beier

Willie Beier

1596728880

Tutorial: Getting Started with R and RStudio

In this tutorial we’ll learn how to begin programming with R using RStudio. We’ll install R, and RStudio RStudio, an extremely popular development environment for R. We’ll learn the key RStudio features in order to start programming in R on our own.

If you already know how to use RStudio and want to learn some tips, tricks, and shortcuts, check out this Dataquest blog post.

Table of Contents

#data science tutorials #beginner #r tutorial #r tutorials #rstats #tutorial #tutorials

Jeromy  Lowe

Jeromy Lowe

1599097440

Data Visualization in R with ggplot2: A Beginner Tutorial

A famous general is thought to have said, “A good sketch is better than a long speech.” That advice may have come from the battlefield, but it’s applicable in lots of other areas — including data science. “Sketching” out our data by visualizing it using ggplot2 in R is more impactful than simply describing the trends we find.

This is why we visualize data. We visualize data because it’s easier to learn from something that we can see rather than read. And thankfully for data analysts and data scientists who use R, there’s a tidyverse package called ggplot2 that makes data visualization a snap!

In this blog post, we’ll learn how to take some data and produce a visualization using R. To work through it, it’s best if you already have an understanding of R programming syntax, but you don’t need to be an expert or have any prior experience working with ggplot2

#data science tutorials #beginner #ggplot2 #r #r tutorial #r tutorials #rstats #tutorial #tutorials

Tutorial: Loading and Cleaning Data with R and the tidyverse

1. Characteristics of Clean Data and Messy Data

What exactly is clean data? Clean data is accurate, complete, and in a format that is ready to analyze. Characteristics of clean data include data that are:

  • Free of duplicate rows/values
  • Error-free (e.g. free of misspellings)
  • Relevant (e.g. free of special characters)
  • The appropriate data type for analysis
  • Free of outliers (or only contain outliers have been identified/understood), and
  • Follows a “tidy data” structure

Common symptoms of messy data include data that contain:

  • Special characters (e.g. commas in numeric values)
  • Numeric values stored as text/character data types
  • Duplicate rows
  • Misspellings
  • Inaccuracies
  • White space
  • Missing data
  • Zeros instead of null values

2. Motivation

In this blog post, we will work with five property-sales datasets that are publicly available on the New York City Department of Finance Rolling Sales Data website. We encourage you to download the datasets and follow along! Each file contains one year of real estate sales data for one of New York City’s five boroughs. We will work with the following Microsoft Excel files:

  • rollingsales_bronx.xls
  • rollingsales_brooklyn.xls
  • rollingsales_manhattan.xls
  • rollingsales_queens.xls
  • rollingsales_statenisland.xls

As we work through this blog post, imagine that you are helping a friend launch their home-inspection business in New York City. You offer to help them by analyzing the data to better understand the real-estate market. But you realize that before you can analyze the data in R, you will need to diagnose and clean it first. And before you can diagnose the data, you will need to load it into R!

3. Load Data into R with readxl

Benefits of using tidyverse tools are often evident in the data-loading process. In many cases, the tidyverse package readxl will clean some data for you as Microsoft Excel data is loaded into R. If you are working with CSV data, the tidyverse readr package function read_csv() is the function to use (we’ll cover that later).

Let’s look at an example. Here’s how the Excel file for the Brooklyn borough looks:

The Brooklyn Excel file

Now let’s load the Brooklyn dataset into R from an Excel file. We’ll use the readxlpackage. We specify the function argument skip = 4 because the row that we want to use as the header (i.e. column names) is actually row 5. We can ignore the first four rows entirely and load the data into R beginning at row 5. Here’s the code:

library(readxl) # Load Excel files
brooklyn <- read_excel("rollingsales_brooklyn.xls", skip = 4)

Note we saved this dataset with the variable name brooklyn for future use.

4. View the Data with tidyr::glimpse()

The tidyverse offers a user-friendly way to view this data with the glimpse() function that is part of the tibble package. To use this package, we will need to load it for use in our current session. But rather than loading this package alone, we can load many of the tidyverse packages at one time. If you do not have the tidyverse collection of packages, install it on your machine using the following command in your R or R Studio session:

install.packages("tidyverse")

Once the package is installed, load it to memory:

library(tidyverse)

Now that tidyverse is loaded into memory, take a “glimpse” of the Brooklyn dataset:

glimpse(brooklyn)
## Observations: 20,185
## Variables: 21
## $ BOROUGH <chr> "3", "3", "3", "3", "3", "3", "…
## $ NEIGHBORHOOD <chr> "BATH BEACH", "BATH BEACH", "BA…
## $ `BUILDING CLASS CATEGORY` <chr> "01 ONE FAMILY DWELLINGS", "01 …
## $ `TAX CLASS AT PRESENT` <chr> "1", "1", "1", "1", "1", "1", "…
## $ BLOCK <dbl> 6359, 6360, 6364, 6367, 6371, 6…
## $ LOT <dbl> 70, 48, 74, 24, 19, 32, 65, 20,…
## $ `EASE-MENT` <lgl> NA, NA, NA, NA, NA, NA, NA, NA,…
## $ `BUILDING CLASS AT PRESENT` <chr> "S1", "A5", "A5", "A9", "A9", "…
## $ ADDRESS <chr> "8684 15TH AVENUE", "14 BAY 10T…
## $ `APARTMENT NUMBER` <chr> NA, NA, NA, NA, NA, NA, NA, NA,…
## $ `ZIP CODE` <dbl> 11228, 11228, 11214, 11214, 112…
## $ `RESIDENTIAL UNITS` <dbl> 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1…
## $ `COMMERCIAL UNITS` <dbl> 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0…
## $ `TOTAL UNITS` <dbl> 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1…
## $ `LAND SQUARE FEET` <dbl> 1933, 2513, 2492, 1571, 2320, 3…
## $ `GROSS SQUARE FEET` <dbl> 4080, 1428, 972, 1456, 1566, 22…
## $ `YEAR BUILT` <dbl> 1930, 1930, 1950, 1935, 1930, 1…
## $ `TAX CLASS AT TIME OF SALE` <chr> "1", "1", "1", "1", "1", "1", "…
## $ `BUILDING CLASS AT TIME OF SALE` <chr> "S1", "A5", "A5", "A9", "A9", "…
## $ `SALE PRICE` <dbl> 1300000, 849000, 0, 830000, 0, …
## $ `SALE DATE` <dttm> 2020-04-28, 2020-03-18, 2019-0…

The glimpse() function provides a user-friendly way to view the column names and data types for all columns, or variables, in the data frame. With this function, we are also able to view the first few observations in the data frame. This data frame has 20,185 observations, or property sales records. And there are 21 variables, or columns.

#data science tutorials #beginner #r #r tutorial #r tutorials #rstats #tidyverse #tutorial #tutorials