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high availability

High availability refers to the ability of a system or application to keep running even if there is a problem or failure. This is important because if a system or application goes down, it can cause problems for those who rely on it. To achieve high availability, multiple copies of the system or application are set up in different locations so that if one fails, the others can take over and keep things running smoothly. This helps ensure that the system or application is always available when needed.

ChatGPT explaining application high availability to a high school kid

Before going into the details, it’s worth figuring out what the application (or system) users need as opposed to what they think they need:

Not surprisingly, IT vendors sell magic infrastructure solutions as the high-availability panacea based on the assumption that redundant infrastructure cannot fail. Nothing could be further from the truth:

High Availability Concepts, Technologies, and Solutions

You can use a plethora of approaches depending on your availability targets:

  • Disaster recovery is the right tool for the job if you’re OK with the system being down for a few hours.
  • Automatic restart of application instances combined with disaster recovery is acceptable if you can accept your system to be down ~0.1% of the time (99.9% availability)
  • Availability targets higher than 99.9% can only be reached reliably with proper application design supported by well-designed infrastructure.

I wrote over 130 blog posts on these topics. It would be impossible to list all of them on a single page; major high-availability technologies or concepts thus have dedicated pages:

One of the prerequisites for highly available services is also redundant networking infrastructure:

Regardless of your approach, the only sustainable way to get highly available services is the correct design of the application stack. For more details, watch the Designing Active-Active and Disaster Recovery Data Centers webinar; I also wrote a few blog posts on the topic:

Notable Outages

Finally, here are a few notable outages. TL&DR: it can happen to the big guys and will eventually happen to you.

Other High Availability Blog Posts

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video

We published hundreds of public videos covering dozens of technologies on ipSpace.net. Networking technologies covered in free videos include:

Contents

Artificial Intelligence and Machine Learning

More in the AI/ML in Networking: The Good, the Bad and the Ugly webinar (with more videos coming soon).

Border Gateway Protocol (BGP)

More in the Network Security Fallacies part of the How Networks Really Work webinar and the Internet Routing Security webinar.

Business Aspects of Networking Technologies

More in the Business Aspects of Networking Technologies webinar.

Cloud Networking

Cumulus Linux

Ethernet VPN (EVPN)

FRRouting

IPv6 Security

More in the IPv6 Security webinar.

Kubernetes

More in the Kubernetes Networking Deep Dive webinar (with more videos coming soon).

Leaf-and-Spine Fabrics

Networking Fundamentals

More in the How Networks Really Work webinar (with more videos coming soon).

Networking Labs

More in the Network Automation Tools webinar (with more videos coming soon).

Software-Defined WAN (SD-WAN)

More in Software-Defined WAN (SD-WAN) Overview, Cisco SD-WAN and Business Aspects of Networking Technologies webinars (with more videos coming soon).

Switching and ASICs

Other Videos or Video-Related Blog Posts

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SD-WAN

Software-Defined WAN (SD-WAN) is the second “software-defined” marketing attempt (after the original SDN) to dress a conglomerate of old technologies into shiny new clothes. Even Wikipedia article promotes some of the usual software-defined hype, quoting Network World claim that:

SD-WAN simplifies the management and operation of a WAN by decoupling the networking hardware from its control mechanism. This concept is similar to how software-defined networking implements virtualization technology to improve data center management and operation.

Is It Real?

Want to know how real those claims are? Start the journey with this series of myth-busting blog posts:

Does SD-WAN make sense? Sure:

Need More Details?

I covered the basics of SD-WAN in Choose the Optimal VPN Service and SDN Use Cases webinars.

Pradosh Mohapatra described the basics of SD-WAN and its typical components and architectures:

Want to know more about Cisco’s SD-WAN solution (formerly known as Viptela)? Enjoy David Peñaloza Seijas’ deep dive into its architecture and implementation details:

Real-Life SD-WAN

SD-WAN sounds great, but does it work as expected? Maybe not:

Is it secure? Some products seem to be nothing more than a bunch of open-source component glued together with clueless Python code:

Some service providers want to use SD-WAN to offer managed services. Not surprisingly, some people1 don’t find that a good idea:

Then there are some technical details vendors love to gloss over:

Does it work within a public cloud? Yeah, sort of… with a few challenges:

Want Even More?

Love marketing-related rants? Here are a few:

Last, but definitely not least, you might enjoy these (more esoteric) solutions:

Blog Posts I Forgot to Categorize

  1. Including those working for said service providers or their customers ↩︎

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