One of the toughest pieces of the puzzle to solve when you are new to Kubernetes is ingress. Firstly, you have native ingress resource types, but you also need to use a controller. There are many third-party ingress controllers available to you, so what’s the difference between them?
Today we’ll breakdown ingress, it’s limitations and how to choose an ingress controller. By the end, you’ll have a grasp of ingress basics and will be ready to continue to advanced Kubernetes ingress problems.
To get the most out of this article, you’ll need some prior understanding of Kubernetes services and namespaces. You can brush up on this knowledge with the previous article in our series, Pods, services, deployments… what do I use when?.
Here’s what we’ll cover today:
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Why do you need ingress in Kubernetes? You could instead just expose the service and specify
type LoadBalancer right?
That would then speak to your cloud of choice and spin up a load balancer for you with a public IP address and your service would be available for consumption. Happy days!!!
Now imagine that you are running 10, or maybe 100 services exposed to the public. Each service would spin up its own load balancer and public IP address. You can see how this would very quickly sprawl and become unmanageable. Not to mention that it will be costing you money from your cloud provider for the extra load balancers and IP addresses.
Ingress allows you to share a single public IP address and route your application via URLs or URI, commonly known as http routing. Once you have an ingress controller picked, you will be able to specify the URLs or URI that you need to route, and the controller will look after it for you.
When using ingress there are a couple of limitations that you really need to be aware of.
The first is that ingress resources are not namespaced. Don’t get me wrong here, the controllers themselves can be namespaced with rbac controls. The definition of the actual ingress resource under Kind: “Ingress can’t not have rbac and is not namespaced.”
So, what does that mean?
This means that if you have multiple teams using the cluster, they will need to be wary of deployments involving ingress as if they have permissions to write their ingress; they will also have permission to change or modify someone else’s on the cluster.
This brings me to the second limitation of ingress; Kubernetes can have multiple of the same ingress types pointing to different resources. Now this can be of use to you, but this can also lead to traffic being routed to rouge services on your cluster that are not meant to be a part of that ingress rule. As mentioned earlier, this is something that you should be aware of when using ingress. Later on in the post, you’ll see some ways to make sure each ingress rule is unique.
In the diagram below, you can see the flow of how requests are coming in from the internet, then hit the ingress controller, and are then routed to the service running on your cluster.
Now that you have a good understanding of the flow of traffic to your service, let’s look at how you can define the ingress resource.
For the examples, I am going to use the Nginx controller which is the easiest to get up and running. In the next section, you’ll find some other controllers to give you options for your cluster.
In the examples below, you’ll see that you can define your ingress rules via two methods: First with URI’s and the second with host headers.
apiVersion: networking.k8s.io/v1beta1 kind: Ingress metadata: name: production-uri annotations: nginx.ingress.kubernetes.io/rewrite-target: / spec: rules: - host: production.com http: paths: - path: /users backend: serviceName: users-api servicePort: 4200 - path: /payments backend: serviceName: payments-api servicePort: 8080
apiVersion: networking.k8s.io/v1beta1 kind: Ingress metadata: name: my-production-v-host spec: rules: - host: foo.production.com http: paths: - backend: serviceName: api-v1 servicePort: 80 - host: bar.production.com http: paths: - backend: serviceName: api-v2 servicePort: 80
In this example, its defining the routing via URL in the host header and your traffic will go to the service defined in the host header.
Choosing an ingress controller will be a personal choice and will depend on your business use case. Here are some that have different options for configurations that are definitely worth a look.
Nginx is one of the easiest to get up and running. It does use the standard Kubernetes resource type, so you would need to implement something like
open policy agent if you wanted to block multiple of the same entries of an ingress rule. Out of the box, Nginx gives you
TLS/HTTPS support, load balancing,
TCP/UDP, and interfaces to Prometheus for metrics which can come in handy.
Contour takes a completely different approach to ingress and uses a new ingress type via CRD’s. Contour fixes the problem of multiple ingress rules by only allowing one rule and also allows you to delegate your URI paths and parts of the URL. Additionally, it uses
envoy as a reverse proxy. This is one that is worth your while researching.
Traefik is another popular choice for ingress and comes packed full of features. Traefik ships with a dashboard that allows you to dig into your ingress rules. There is also integrations with tracing (Jaeger, Open tracing and Zipkin), metrics (
Depending on your business use case, you should definitely do some research on the open-source projects above for your ingress needs.
Congratulations on taking another step toward learning Kubernetes by demystifying ingress. Unfortunately, Kubernetes is a notoriously difficult software to learn, with many required unique skills, like using ingress, and years of best practices to learn.
To help you tackle ingress and other complicated Kubernetes topics, Educative has created A Practical Guide to Kubernetes.
This course, written by Kubernetes expert and Docker Captain, Viktor Faric, is packed engaging explinations and interactive examples to get you onboard with Kubernetes quickly. You’ll start with the basics solidifying your foundation of pods and clusters, before moving on to advanced topics like ingress, resource management, and config maps.
By the end, you’ll have an understanding of all professionally used concepts in Kubernetes as well as created and deployed many of your very own clusters!
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