Building a scalable application that has high availability is not easy. Problems can crop up in unexpected ways that can cause your application to stop working and stop serving your customer’s needs.

No one can anticipate where problems will come from and no amount of testing will identify and correct all issues. Some issues end up being systemic problems that require the correlation of multiple systems in order for the problems to occur. Some are more basic, but are simply missed or not anticipated.

Links and More Information

The following are links mentioned in this episode, and links to related information:

• Modern Digital Applications Website (https://mdacast.com)
• Lee Atchison Articles and Presentations (https://leeatchison.com)
• Architecting for Scale, published by O’Reilly Media (https://architectingforscale.com)

Application availability is critical to all modern digital applications. But how do you avoid availability problems? You can do so by avoiding those traps that cause poor availability.

There are five main causes of poor availability that impact modern digital applications.

Poor Availability Cause Number 1

Often, the main driver of application failure is success. The more successful your company is, the more traffic your application will receive. The more traffic it receives, the more likely you will run out of some vital resource that your application requires.

Typically, resource exhaustion doesn’t happen all at once. Running low on a critical resource can cause your application to begin to slow down, backlogging requests. Backlogged requests generate more traffic, and ultimately a domino effect drives your application to fail.

But even if it doesn’t fail completely, it can slow down enough that your customers leave. Shopping carts are abandoned, purchases are left uncompleted. Potential customers go elsewhere to find what they are looking for.

Increasing the number of users using your system or increase the amount of data these consumers are using in your system, and your application may fall victim to resource exhaustion. Resource exhaustion can result in a slower and unresponsive application.

Poor Availability Cause Number 2

When traffic increases, sometimes assumptions you’ve made in your code on how your application can scale are proven to be incorrect. You need to make adjustments and optimizations on the fly in order to resolve or work around your assumptions in order to keep your system performant. You need to change your assumptions on what is critical and what is not.

The realization that you need to make these changes usually comes at an inopportune time. They come when your application is experiencing high traffic and the shortcomings start becoming exposed. This means you need a quick fix to keep things operating.

Quick fixes can be dangerous. You don’t have time to architect, design, prioritize, and schedule the work. You can’t think through to make sure this change is the right long term change You need to make changes now to keep your application afloat.

These changes, implemented quickly and at the last minute with little or no forethought or planning, are a common cause of problems. Untested and limited tested fixes, quickly thought through fixes, bad deployments caused my skipping important steps. All of these things can introduce defects into your production environment. The fact that you need to make changes to maintain availability, will itself threaten your availability.

Poor Availability Cause Number 3

When an application becomes popular, your business needs usually demand that your...