Designing a Zero-Downtime System in Kubernetes
August 18, 2020

Gigi Sayfan
Author of "Mastering Kubernetes"

The following is an excerpt from my book, Mastering Kubernetes:

There is no such thing as a zero-downtime system. All systems fail and all software systems definitely fail. Sometimes the failure is serious enough that the system or some of its services will be down. Think about zero downtime as a best-effort distributed system design.

You design for zero downtime in the sense that you provide a lot of redundancy and mechanisms to address expected failures without bringing the system down. As always, remember that, even if there is a business case for zero downtime, it doesn't mean that every component must have zero downtime. Reliable (within reason) systems can be constructed from highly unreliable components.

The plan for zero downtime is as follows:

Redundancy at every level

This is a required condition. You can't have a single point of failure in your design because when it fails, your system is down.

Automated hot swapping of failed components

Redundancy is only as good as the ability of the redundant components to kick into action as soon as the original component has failed. Some components can share the load (for example, stateless web servers), so there is no need for explicit action. In other cases, such as the Kubernetes scheduler and controller manager, you need a leader election in place to make sure the cluster keeps humming along.

Tons of metrics, monitoring, and alerts to detect problems early

Even with careful design, you may miss something or some implicit assumption might invalidate your design. Often, such subtle issues creep up on you and with enough attention, you may discover it before it becomes an all-out system failure.

For example, suppose there is a mechanism in place to clean up old log files when disk space is over 90% full, but for some reason, it doesn't work. If you set an alert for when disk space is over 95% full, then you'll catch it and be able to prevent the system failure.

Tenacious testing before deployment to production

Comprehensive tests have proven themselves as a reliable way to improve quality. It is hard work to have comprehensive tests for something as complicated as a large Kubernetes cluster running a massive distributed system, but you need it.

What should you test? Everything. That's right. For zero downtime, you need to test both the application and the infrastructure together. Your 100% passing unit tests are a good start, but they don't provide much confidence that when you deploy your application on your production Kubernetes cluster, it will still run as expected.

The best tests are, of course, on your production cluster after a blue-green deployment or identical cluster. In lieu of a full-fledged identical cluster, consider a staging environment with as much fidelity as possible to your production environment. Here is a list of tests you should run. Each of these tests should be comprehensive because if you leave something untested, it might be broken:

• Unit tests

• Acceptance tests

• Performance tests

• Stress tests

• Rollback tests

• Data restore tests

• Penetration tests

Does that sound crazy? Good. Zero-downtime, large-scale systems are hard. There is a reason why Microsoft, Google, Amazon, Facebook, and other big companies have tens of thousands of software engineers (combined) just working on infrastructure, operations, and making sure things are up and running.

Keep the raw data

For many systems, the data is the most critical asset. If you keep the raw data, you can recover from any data corruption and processed data loss that happens later. This will not really help you with zero downtime because it can take a while to re-process the raw data, but it will help with zero data loss, which is often more important. The downside to this approach is that the raw data is often huge compared to the processed data. A good option may be to store the raw data in cheaper storage compared to the processed data.

Perceived uptime as a last resort

OK. Some part of the system is down. You may still be able to maintain some level of service. In many situations, you may have access to a slightly stale version of the data or can let the user access some other part of the system. It is not a great user experience, but technically the system is still available.

Gigi Sayfan is a software engineer and author of the book "Mastering Kubernetes"
Share this

Industry News

May 25, 2022

JFrog introduced Project Pyrsia, an open-source software community initiative that utilizes blockchain technology to secure software packages (A.K.A Binaries) from vulnerabilities and malicious code.

May 25, 2022

Kasm Technologies, in partnership with Docker, has developed Kasm Workspaces as a Containerized Desktop Infrastructure platform for streaming remote workspaces directly to your web browser.

May 25, 2022

Cascadeo announced the integration of Amazon DevOps Guru with cascadeo.io, Cascadeo’s cloud monitoring and management platform that provides users with a single view of multi-cloud or hybrid infrastructure environments.

May 24, 2022

Oracle announced the availability of Java 18, the latest version of the programming language and development platform.

May 24, 2022

Docker announced the acquisition of Tilt, makers of a development environment as code for teams on Kubernetes.

May 24, 2022

F5 announced the release of F5 NGINX for Microsoft Azure, an Azure-native service offering developed in partnership with Microsoft, that helps customers deliver modern applications on Azure with just a few clicks.

May 24, 2022

Pegasystems announced a strategic partnership with Google Cloud that will help enable joint clients to accelerate their digital transformations with Pega’s low-code enterprise software on Google Cloud’s highly scalable cloud services.

May 23, 2022

Sauce Labs announced the release of contract testing with mocking on the Sauce Labs API Testing Platform.

May 23, 2022

Pure Storage announced a series of updates to its Portworx portfolio.

May 23, 2022

StackHawk has secured $20.7 million in capital.

May 19, 2022

Jellyfish announced the launch of Jellyfish Benchmarks, a way to add context around engineering metrics and performance by introducing a method for comparison.

May 19, 2022

Solo.io announced the addition and integration of Cilium networking into its Gloo Mesh platform, providing a complete application-networking solution for companies’ cloud-native digital transformation efforts.

May 19, 2022

Aqua Security announced multiple updates to Aqua Trivy, making it a unified scanner for cloud native security.

May 18, 2022

Red Hat unveiled updates across its portfolio of developer tools designed to help organizations build and deliver applications faster and more consistently across Kubernetes-based hybrid and multicloud environments.

May 18, 2022

Armory announced public early access to their new Continuous Deployment-as-a-Service product.