Guest post originally published on the NGINX blog by Jenn Gile, Manager, Product Marketing at F5

This is the first blog post in our series on how to choose a Kubernetes Ingress controller.

When organizations first start experimenting with Kubernetes, they often don’t put a lot of thought into the choice of Ingress controller. They might think that all Ingress controllers are alike, and in the interests of getting up and running quickly it’s easiest to stick with the default Ingress controller for the Kubernetes framework they did choose. And it’s true that just about any Ingress controller is fine in testing or low‑volume production environments. But as you scale, your choice of Ingress controller becomes more important. That’s because Ingress controllers can provide much more than the basic functionality of moving your traffic from point A to point B.

From advanced traffic management to visibility to built‑in security, an Ingress controller can be one of the most powerful tools in your Kubernetes stack. In fact, at F5 NGINX we consider it to be the foundation of any production‑grade Kubernetes deployment. But many developers and Platform Ops teams don’t realize the full power of an Ingress controller – or the consequences of choosing one that can’t scale. Choosing an Ingress controller that doesn’t scale well or protect complex environments can prevent you from getting Kubernetes out of testing and into production. In this blog series we aim to educate you on the basics of Ingress controllers and how to make a wise choice that delivers the functionality and security you need, today and tomorrow.

What’s an Ingress Controller?

An Ingress controller is a specialized load balancer that manages the Layer 4 and 7 traffic entering Kubernetes clusters, and potentially the traffic exiting them. So that we’re all on the same page, here are the terms we use at NGINX (and they’re largely the same across the industry):

Why Do You Need an Ingress Controller?

By default, applications running in Kubernetes pods (containers) are not accessible from the external network, but only from other pods within the Kubernetes cluster. Kubernetes has a built‑in configuration object for HTTP load balancing, called Ingress, which defines how entities outside a Kubernetes cluster can connect to the pods represented by one or more Kubernetes services.

When you need to provide external access to your Kubernetes services, you create an Ingress resource to define the connectivity rules, including the URI path, backing service name, and other information. On its own, however, the Ingress resource doesn’t do anything. You must deploy and configure an Ingress controller application (using the Kubernetes API) to implement the rules defined in Ingress resources.

What Does an Ingress Controller Do?

Infograph showing what an Ingress Controller does

When it’s time to select an Ingress controller, it can be tempting to start with a feature list, but you might end up with an Ingress controller that has fantastic features but doesn’t satisfy your business needs. Instead make sure to explore two elements that impact how well the Ingress controller will work for your team and your apps: use cases (what problems it will solve) and resourcing (how you’re going to “pay” for it). We’ll cover these two topics in the remainder of this blog.

What Problems Do You Want the Ingress Controller to Solve?

The core use case for an Ingress controller is traffic management, so you probably want the Ingress controller to handle one or more of these common use cases:

But there’s no reason to settle for a “one‑trick pony” – most Ingress controllers can do more than manage traffic. By using the Ingress controller to solve multiple problems, not only do you reduce the size and complexity of your stack, but you can also offload non‑functional requirements from the apps to the Ingress controller. Let’s look at four non‑traditional Ingress controller use cases that can help make your Kubernetes deployments more secure, agile, and scalable while making more efficient use of your resources.

Monitoring and Visibility

Lack of visibility into the Kubernetes cluster is one of the biggest challenges in production environments, contributing to difficulty with troubleshooting and resiliency. Because Ingress controllers operate at the edge of your Kubernetes clusters and touch every bit of traffic, they’re well situated to provide data that can help you troubleshoot (and even avoid) two common problems: slow apps and resource exhaustion in the Kubernetes cluster or platform. For Ingress controller to improve visibility, it needs to:

API Gateway

Unless you’re looking to perform request‑response manipulation in Kubernetes, it’s very likely that the Ingress controller can double as your API gateway. Depending on its feature set, an Ingress controller might be able to provide core API gateway functions including TLS termination, client authentication, rate limiting, fine‑grained access control, and request routing at Layers 4 through 7.

Authentication and Single Sign‑On

Offloading authentication of login credentials from your Kubernetes services to your Ingress controller can solve two issues.

Web Application Firewall Integration

It’s not that an Ingress controller can serve as a web application firewall (WAF), but rather that the WAF can be consolidated with the Ingress controller. Although a WAF can be deployed at many places outside and within Kubernetes, for most organizations the most efficient and effective location is in the same pod as the Ingress controller. This use case is perfect when security policies are under the direction of SecOps or DevSecOps and when a fine‑grained, per‑service or per‑URI approach is needed. It means you can use the Kubernetes API to define policies and associate them with services. Further, the Ingress controller’s role‑based access control (RBAC) functionality can enable SecOps to enforce policies per listener while DevOps users set policies per Ingress resource.

How Are You Going to Resource the Ingress Controller?

Every Ingress controller comes at a cost…even those that free and open source (perhaps you’ve heard the phrase “free like a puppy”). Some costs can be assigned predictable dollar amounts as line items in your budget, while others depend on how much time your team has to spend dealing with the consequences of which Ingress controller you choose (increased complexity, lack of portability, and so on). Let’s look at the costs – in terms of both time and money – to consider when budgeting for an Ingress controller: time and money.

Resource the Ingress Controller by budgeting for capital costs or time costs

Budgeting for Time Costs

Budgeting for headcount can be far more challenging than for fixed‑cost line items, especially when you’re trying to resource a project in an unfamiliar space. You need to ask questions like:

A Note on Kubernetes Tool Ownership

We’ve observed a trend in the industry toward consolidating tools and ownership under the domain of NetOps teams. While this can go a long way towards simplifying your stack and improving security, we advocate for thoughtful duplication of tools based on team goals. It makes sense to have NetOps team manage perimeter tools (like external load balancers) because they focus on the broader platform, but DevOps teams care most about the services deployed close to the app code and need more agility and finer‑grained control than they get from NetOps tools. Kubernetes tools, including the Ingress controller, have the best chance of success when they’re selected by DevOps. That’s not to say you must grant developers complete freedom of choice for tools! Some brutal standardization of tooling within Kubernetes is still a best practice.

Budgeting for Capital Costs

When organizations first experiment with Kubernetes, they often don’t budget much for tools or support. If you have the people resources to truly support an Ingress controller that needs more “hand holding”, then no monetary budget is okay…at first. But as your Kubernetes investment increases, you may find yourself limited by the tool’s features, or wanting to dedicate your team to other priorities. That’s when the scale tips towards paying for an easier-to-use, more stable tool with enterprise features and support.

When you’re ready to pay for an Ingress controller, be aware that the licensing model matters. Based on traditional pricing models outside of Kubernetes, pricing for Ingress controllers is often “per instance” or “per Ingress proxy”. While there are use cases when this still makes sense in Kubernetes, licensing an Ingress controller on a “per cluster” basis instead means you pay based on application tenancy rather than “number of proxies.”

Here are our recommendations for different scenarios:

Next Steps: Risk Tolerance and Future‑Proofing

Now that you have a grasp on your requirements, the next step is to decide as a team what your tolerance is for the risks an Ingress controller might introduce, and to figure out how you’ll need the Ingress controller to scale as you grow your Kubernetes deployment. We take up those topics in Part 2.