HA vs. DR: 6 Reasons Why High Availability Just Isn’t Good Enough

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High availability vs. disaster recovery might seem like substitutes for each other on the surface, but read on to learn why your organization needs both solutions in place to ensure business continuity.

There continues to be a great deal of confusion between high availability (HA) and disaster recovery (DR). Both are considered business continuity solutions and both work to ensure availability. But that is where the similarities end.

Unfortunately, the conflation of the two and the pressure to keep IT costs down often lead companies to choose just one of them. And in this scenario, many companies choose HA because the impact of not having HA is felt more immediately.

But in the wake of troubling DDos attacks and other massive outages, developers can’t afford to falter in continuity planning and should make sure they fully understand both HA and DR — and the critical need for both.

Related: Get best practices and essential tips for your Disaster Recovery evaluation process directly from companies that have recently changed their DR strategy.

To better understand why HA just isn’t good enough when used on its own for business continuity, read on.

1. High Availability Won’t Help You When Disaster Strikes
On the surface, both HA and DR aim to achieve application continuity. However, their technical goals are not the same. HA focuses on uptime on a day-to-day basis. Throughout daily operation, an application with HA will guarantee four-nines of uptime (or even six-nines for some companies). However, HA planning doesn’t take disasters into consideration.

DR planning is for recovery in extreme cases of downtime — like when the Internet of Things attack brought down so many of the world’s biggest websites. For disaster recovery, RPO and RTO are most important:

  • Recovery Point Objective (RPO): The time during a disaster before the amount of data lost exceeds the tolerance threshold outlined in the business continuity plan.
  • Recovery Time Objective (RTO): The actual time in which an application or service must be recovered according to the business continuity plan.

Reaching your RPO and RTO requires a DR solution. The more aggressive your objectives, the more robust a DR solution you need. HA won’t help you here.

2. High Availability Only Works for Routine Scenarios
Another reason why HA and DR can’t replace one another is that they safeguard applications against different scenarios. HA only protects applications from expected, routine failures or challenges. For example:

  • Single hardware component failures: These can occur in a number of areas for a particular application, such as network fails, CPU malfunctions, or repeated disk errors. In all of these situations, HA can respond quickly in order to maintain application uptime.
  • Variable load increases: Traffic spikes are a fact of life for so many business applications. With HA, autoscaling or redundant servers are in place for handling increased loads.
  • Network splits: When different parts of an application aren’t able to communicate with one another, HA solutions allow them to continue functioning.

DR scenarios, on the other hand, are more intermittent in nature:

  • Critical bugs in the application: Given the demand for faster application delivery, releases are seldom perfect. Quality assurance and testing go a long way toward expelling bugs, but some undoubtedly slip through. Critical bugs can cause an entire application to go down. In these situations, DR is necessary to maintain service continuity.
  • Human errors in operation: As much as we rely on automation in IT operations, human errors still cause problems, as in the case of the recent GitLab outage. One misconfigured server or accidental release of old code can disrupt service across your entire organization. When your DR solution has a replicated version of your application ready to be spun up in disaster scenarios, your business can keep functioning without losing time, money, or your good reputation.
  • Security breaches: No company is immune to cyber attacks. Whether it’s a DDoS attack or another type of data breach, you can’t afford to lose service in the wake of a security incident. These intermittent issues can be mitigated by having a DR solution in place.

3. High Availability Doesn’t Prevent Data Loss
When you’re implementing HA in your application, uptime is your main objective. You want to make sure that you can maintain availability despite momentary infrastructure failures. However, uptime doesn’t protect you from data loss.

When your DR solution fails over to a secondary location, you’re protecting your business from data loss. Robust DR solutions provide real-time replication of all your data in a separate recovery site. Moreover, DR provides point-in-time recovery, which enables you to restore an earlier version of your data, which is critical in cases of ransomware, late discovery of data loss, and data corruption.

4. High Availability Doesn’t Take Human Errors Into Consideration
The goal of HA is to achieve sub-second response times for resiliency. This means HA relies on your application infrastructure for automated responses to disruption.

The fact that a person decides if and when to launch DR enables human discretion, which is often needed in complex technological environments. For example, if someone deletes an entire database by mistake, HA will make the deleted database available (which doesn’t help anyone), whereas a robust DR tool will enable you to recover an earlier version of the database, thereby saving all of the data.

5. Only DR Provides Recovery for Your Mission-Critical Applications
When you implement HA for an application, it usually means that the application is mission-critical for your business. If your application is important enough to warrant HA, you’ll most likely want to have DR in place as well. The only problem is that if you haven’t realized this relationship, you may not understand the need for DR until it’s too late and disaster has already struck.

6. High Availability and Disaster Recovery Need Each Other
When you have HA built into your application but don’t have a DR strategy, you can maintain uptime despite semi-regular, minor errors and disruptions. The problem is that serious disasters can leave your application down for an extended period of time. Even worse, they can result in large volumes of data loss, which is why you need disaster recovery.

When you have DR but don’t have an HA strategy, your production system may be repeatedly unavailable. Any common system component failure results in downtime until your IT team can respond. This is why HA and DR are such strong complements in so many situations.

To learn how your organization can implement enterprise-grade DR without breaking the bank, download this free white paper.