Mastering Kubernetes with Custom Schedulers: A Story for Engineering Leaders

Imagine you’re the Engineering Manager of a fast-growing tech company. Your team is responsible for running a suite of applications on Kubernetes, and everything seems to be going well - until it isn’t. Suddenly, a critical service goes down because it couldn’t get the resources it needed, while lower-priority workloads hogged valuable compute power. Now, you’re facing a production incident and a frustrated product team asking why their mission-critical workload wasn’t prioritized. Sound familiar?

In situations like this, Kubernetes’ default scheduling can feel like a black box - effective for standard cases but not always aligned with your unique business priorities. That’s where custom schedulers come into play. Today, let’s explore a story of how custom schedulers helped an organization like yours take control of their workloads, save money, and ensure critical services always got the attention they deserved.

The Default Scheduler Dilemma

Our story starts with a company named Tecknobody (Fictional), a mid-sized enterprise specializing in financial technology. Tecknobody had adopted Kubernetes to scale their services and reduce manual overhead. At first, everything seemed great - Kubernetes made it easy to deploy applications, and the default scheduler worked well enough for most use cases. But as the business grew, so did the complexity of their infrastructure.

One day, during a high-stakes product demo, their flagship application suffered a significant slowdown. Investigations revealed that a batch of non-critical analytics jobs was taking up the majority of the cluster’s resources. The default Kubernetes scheduler had assigned these batch jobs to nodes with the most available resources, inadvertently starving the high-priority application of the compute it needed to run smoothly. This left Tecknobody’s leadership questioning whether Kubernetes was the right choice for their critical infrastructure.

The Custom Scheduler Solution

Enter Enna, Tecknobody’s Engineering Manager. Enna realized that while Kubernetes was a powerful tool, its default scheduling wasn’t quite tailored to their business needs. She knew that they needed a better way to ensure critical applications were prioritized, especially during peak times. After some research, Enna and her team decided to build a custom scheduler.

The custom scheduler allowed them to define specific rules for workload placement. By implementing a custom scheduling algorithm, they could ensure that mission-critical workloads always had the resources they needed, while less critical batch processes were scheduled with a lower priority. This not only resolved their immediate problem but also brought a sense of control back to the engineering team.

The Journey to Building a Custom Scheduler

Enna’s team started by understanding the scheduler framework that Kubernetes offers. They learned that Kubernetes allows multiple schedulers to run simultaneously in a cluster, meaning they could deploy their own custom scheduler alongside the default one. By specifying a different `schedulerName` in their pod definitions, they could dictate which pods would use the new custom logic.

Tecknobody’s custom scheduler was written in Go using the Kubernetes scheduler framework. It wasn’t an easy journey - Enna had to ensure her team understood the intricacies of scheduling cycles, including filtering nodes, scoring potential candidates, and ultimately binding pods to nodes. They created a set of custom plugins that allowed them to filter and score nodes based on more granular criteria: prioritizing critical workloads, minimizing cost by consolidating non-critical jobs during off-hours, and maintaining compliance by ensuring data-sensitive applications only ran in approved regions.

The Payoff: Control, Efficiency, and Peace of Mind

The impact was immediate. With the custom scheduler in place, Tecknobody could ensure that their flagship application always had priority access to the resources it needed. This translated into a smoother product demo, happier stakeholders, and a more reliable customer experience. Enna’s team also managed to reduce cloud costs by consolidating workloads more efficiently and strategically scaling down non-essential processes during low-demand periods.

For Tecknobody, the custom scheduler became more than just a tool - it was a strategic differentiator. The ability to exert fine-grained control over resource allocation helped align the engineering strategy with business goals. Instead of struggling to work within the limitations of the default Kubernetes scheduler, Enna’s team had created a solution that allowed them to focus on delivering value rather than firefighting infrastructure issues.

Why This Matters for You as an Engineering Leader

As an Engineering Manager or above, you’re likely balancing the needs of multiple teams and managing conflicting priorities. Kubernetes is an amazing tool, but its default settings are designed to fit general scenarios -not the specific needs of your business. Custom schedulers give you the power to implement your own business rules at the infrastructure level.

• Mission-Critical Focus: Ensure that your high-priority applications always get the resources they need, reducing the risk of downtime or degraded performance during crucial moments.

• Cost Savings: Implement logic that takes advantage of low-cost nodes for non-critical workloads, ultimately optimizing your cloud spend.

• Compliance and Control: Enforce data sovereignty requirements by using custom scheduling rules that are impossible to implement with the default scheduler.

The challenges you face aren’t just technical — they’re deeply tied to the outcomes your business wants to achieve. By adopting custom schedulers, you can create a tailored infrastructure that empowers your team, minimizes surprises, and directly contributes to the goals of your organization.

Wrapping Up: The Power of Customization

For Tecknobody, investing in a custom scheduler meant they could move from reacting to infrastructure problems to proactively managing them. For Enna, it meant peace of mind - knowing her team had built a system that aligned perfectly with the business’s unique needs.

If your organization has found itself limited by Kubernetes’ default behavior, it might be time to consider whether a custom scheduler could give you the competitive edge you need. As a leader, embracing this level of customization can be the key to unlocking better efficiency, more predictable performance, and ultimately, happier customers.

Key Learnings: How to Approach and Solve Problems Like an Engineering Leader

1. Understand the Problem Before Blaming the Tool
   Tools like Kubernetes are designed to be general-purpose, but your specific use case might reveal limitations. Take time to investigate the root cause of issues instead of assuming the tool is at fault.

2. Align Infrastructure Decisions with Business Goals
   Engineering challenges are rarely just technical. Consider the broader impact on your business priorities, like cost efficiency, reliability, and compliance, when designing solutions.

3. Research and Explore Alternatives
   Before dismissing the tool, explore its advanced features or alternative approaches. Kubernetes’ custom scheduler framework, for instance, provides a robust way to tailor resource management to your needs.

4. Collaborate and Upskill Your Team
   Complex challenges often require stepping into new territory, like building custom schedulers. Invest in your team’s growth by encouraging learning and experimentation.

5. Think Proactively, Not Reactively
   Instead of waiting for incidents to dictate your next steps, anticipate potential bottlenecks and design systems to mitigate them. This mindset turns firefighting into strategic planning.

6. Leverage the Power of Customization
   One size rarely fits all in engineering. Customization can bridge the gap between default behavior and the unique requirements of your business. Don’t hesitate to tailor solutions to fit your needs.

7. Iterate and Improve Continuously
   The first implementation may not be perfect, but it will serve as a foundation for future improvements. Focus on delivering incremental value while refining your approach over time.

8. Share Knowledge and Learnings
   Challenges and their solutions are opportunities for growth - not just for your team, but for the broader engineering community. Sharing your story helps others navigate similar hurdles and fosters collective innovation.