I don't know if I missed something, but I can't seem to find any posts/doc that is related to my question. Maybe I misunderstand the type ingress in kubernetes, but is it possible to define multiple ingresses that use the same LoadBlancer? Having to start one LoadBalancer for every ingress is costly.
One of the benefit of using ingress it helps to avoid creating an external LoadBalancer for each LoadBalancer type service. On many cloud providers some of the ingress controllers will create the corresponding external Load Balancer resource for each ingress resource. But using Nginx Ingress controller you need one loadBalancer to expose the Nginx Ingress controller itself. Then create multiple ingress resource and have multiple backends. All the backends are served by same external Load Balancer.
From the docs of Nginx Ingress
In this section you can find a common usage scenario where a single
load balancer powered by ingress-nginx will route traffic to 2
different HTTP backend services based on the host name
Related
I came to know that Nginx Ingress talks directly to pods NOT through a service.
Why endpoints and not services
The NGINX ingress controller does not use Services to route traffic to the pods. Instead it uses the Endpoints API in order to bypass kube-proxy to allow NGINX features like session affinity and custom load balancing algorithms.
Is this specific to this type of ingress or the idea is applicable to all ingresses?
In GKE Ingress documentation
it states that:
When you create an Ingress object, the GKE Ingress controller creates a Google Cloud HTTP(S) Load Balancer and configures it according to the information in the Ingress and its associated Services.
To me it seems that I can not have multiple ingress resources with single GCP ingress controller. Instead, GKE creates a new ingress controller for every ingress resource.
Is this really so, or is it possible to have multiple ingress resources with a single ingress controller in GKE?
I would like to have one GCP LoadBalancer as ingress controller with static IP and DNS configured, and then have multiple applications running in cluster, each application registering its own ingress resource with application specific host and/or path specifications.
Please note that I'm very new to GKE, GCP and Kubernetes in general, so it might be that I have misunderstood something.
I think the question you're actually asking is slightly different than what you have written. You want to know if multiple Ingress resources can be linked to a single GCP Load Balancer, not GKE Ingress controller. Based on the concept of a controller, there is only one GKE Ingress controller in a cluster, which is responsible for fulfilling multiple resources and provisioning multiple load balancers.
So, to answer the question directly (because I've been searching for a straight answer for a long time!):
Combining multiple Ingress resources into a single Google Cloud load
balancer is not supported.
Source: https://cloud.google.com/kubernetes-engine/docs/concepts/ingress
Sad.
However, using the nginx-ingress controller is one way to at least minimize the number of external (GCP) load balancers provisioned (it only provisions a single TCP load balancer), but since the load balancer is for TCP traffic, it cannot terminate SSL, or apply Firewall rules for you (Cloud Armor cannot be used, for instance).
The only way I know of to have a single HTTPS load-balancer in GCP terminate SSL and route traffic to multiple services in GKE is to combine the ingresses into a single resource with all paths and certificates defined in one place.
(If anybody figures out a way to do it with multiple separate ingress resources, I'd love to hear it!)
Yes it is possible to have the single ingress controller for multiple ingress resources.
You can create multiple ingress resources as per path requirement and all will be managed by single ingress controller.
There are multiple ingress controller options also available you can use Nginx also that will create one LB and manage the paths.
Inside Kubernetes if you are creating a service with type LoadBalancer it will create the new LB resource in GCP so make sure your microservice type is ClusterIP and your all traffic goes inside K8s cluster via ingress path.
When you setup the ingress controller it will create one service with type LoadBalancer you can can use that IP in DNS servers to forward the subdomain and path to K8s cluster.
For a sample microservice based architecture deployed on Google kubernetes engine, I need help to validate my understanding :
We know services are supposed to load balance traffic for pod replicaset.
When we create an nginx ingress controller and ingress definitions to route to each service, a loadbalancer is also setup automatically.
had read somewhere that creating nginx ingress controller means an nginx controller (deployment) and a loadbalancer type service getting created behind the scene. I am not sure if this is true.
It seems loadbalancing is being done by services. URL based routing is
being done by ingress controller.
Why do we need a loadbalancer? It is not meant to load balance across multiple instances. It will just
forward all the traffic to nginx reverse proxy created and it will
route requests based on URL.
Please correct if I am wrong in my understanding.
A Service type LoadBalancer and the Ingress is the way to reach your application externally, although they work in a different way.
Service:
In Kubernetes, a Service is an abstraction which defines a logical set of Pods and a policy by which to access them (sometimes this pattern is called a micro-service). The set of Pods targeted by a Service is usually determined by a selector (see below for why you might want a Service without a selector).
There are some types of Services, and of them is the LoadBalancer type that permit you to expose your application externally assigning a externa IP for your service. For each LoadBalancer service a new external IP will be assign to it.
The load balancing will be handled by kube-proxy.
Ingress:
An API object that manages external access to the services in a cluster, typically HTTP.
Ingress may provide load balancing, SSL termination and name-based virtual hosting.
When you setup an ingress (i.e.: nginx-ingress), a Service type LoadBalancer is created for the ingress-controller pods and a Load Balancer in you cloud provider is automatically created and a public IP will be assigned for the nginx-ingress service.
This load balancer/public ip will be used for incoming connection for all your services, and nginx-ingress will be the responsible to handle the incoming connections.
For example:
Supose you have 10 services of LoadBalancer type: This will result in 10 new publics ips created and you need to use the correspondent ip for the service you want to reach.
But if you use a ingress, only 1 IP will be created and the ingress will be the responsible to handle the incoming connection for the correct service based on PATH/URL you defined in the ingress configuration. With ingress you can:
Use regex in path to define the service to redirect;
Use SSL/TLS
Inject custom headers;
Redirect requests for a default service if one of the service failed (default-backend);
Create whitelists based on IPs
Etc...
A important note about Ingress Load balancing in ingress:
GCE/AWS load balancers do not provide weights for their target pools. This was not an issue with the old LB kube-proxy rules which would correctly balance across all endpoints.
With the new functionality, the external traffic is not equally load balanced across pods, but rather equally balanced at the node level (because GCE/AWS and other external LB implementations do not have the ability for specifying the weight per node, they balance equally across all target nodes, disregarding the number of pods on each node).
An ingress controller(nginx for example) pods needs to be exposed outside the kubernetes cluster as an entry point of all north-south traffic coming into the kubernetes cluster. One way to do that is via a LoadBalancer. You could use NodePort as well but it's not recommended for production or you could just deploy the ingress controller directly on the host network on a host with a public ip. Having a load balancer also gives ability to load balance the traffic across multiple replicas of ingress controller pods.
When you use ingress controller the traffic comes from the loadBalancer to the ingress controller and then gets to backend POD IPs based on the rules defined in ingress resource. This bypasses the kubernetes service and load balancing(by kube-proxy at layer 4) offered by kubernetes service.Internally the ingress controller discovers all the POD IPs from the kubernetes service's endpoints and directly route traffic to the pods.
It seems loadbalancing is being done by services. URL based routing is being done by ingress controller.
Services do balance the traffic between pods. But they aren't accessible outside the kubernetes in Google Kubernetes Engine by default (ClusterIP type). You can create services with LoadBalancer type, but each service will get its own IP address (Network Load Balancer) so it can get expensive. Also if you have one application that has different services it's much better to use Ingress objects that provides single entry point. When you create an Ingress object, the Ingress controller (e.g. nginx one) creates a Google Cloud HTTP(S) load balancer. An Ingress object, in turn, can be associated with one or more Service objects.
Then you can get the assigned load balancer IP from ingress object:
kubectl get ingress ingress-name --output yaml
As a result your application in pods become accessible outside the kubernetes cluster:
LoadBalancerIP/url1 -> service1 -> pods
LoadBalancerIP/url2 -> service2 -> pods
I'm not sure how load balancing works with Ingress.
If I understand correctly, what happens is actually something like this:
I fail to see how the load balancing is performed.
What is wrong in the above scheme that I have drawn?
Can you help me rectify it?
Notes:
- The following answer tells me that the Ingress controller itself is of type 'loadbalancer': Ingress service type
- I use kind ClusterIP because I don't want to expose the loadbalancer to the outside world. The following article does not support this claim, where the load balancer would be provided by the service:
https://medium.com/google-cloud/kubernetes-nodeport-vs-loadbalancer-vs-ingress-when-should-i-use-what-922f010849e0
The ClusterIP services themselves perform load balancing. The naming can be confusing as LoadBalancer services are not the only services that involve load balancing - LoadBalancer actually means something more like 'cloud provider please create an external load balancer and point it at this service'. The kubernetes ClusterIP services also load-balance across Pods in different Nodes using the kube-proxy. If you don't want kubernetes to do load balancing then you have to specifically disable it by creating a headless service.
It seems like the first scheme you drew is correct. But I think you get confused in terminology. Particularly in the difference between ingress and ingress-controller.
Ingress is a type of resources in k8s (like Service, Deployment, ReplicaSet etc). We use ingress if we want to expose some services to an external world with binding to some path and host (i.e. myapp.com/api -> my-api-service).
The job of ingress-controller is to handle creation/update/deletion of ingress resources and implement all the functionality needed for ingress. Under the hood ingress-controller is a simple deployment exposed as LoadBalancer or NodePort service depending on where k8s is deployed. And image-controller forwards received request further to one of pods of service which matches host and path in some of the deployed ingress resources.
I got curious and thought: why would I need an Ingress for load balancing on layer 7 if the only thing it does is forward the traffic to a Service that implements the load balancing on layer 4?
Most Ingress controller implementations I looked up, talk to the Kubernetes API server to keep track of all Pods associated with a Service. Instead of forwarding traffic to the Service, they skip the intermediary and directly forward to the Pods. Since an ingress controller operates on layer 7, it enables a more application-oriented load balancing.
I understood Ingress can be used when we want to expose multiple service/routes with a single Load Balancer / public IP.
Now I want to expose my Nginx server to public. I have two choices
Set service type as LoadBalancer voila I got public IP
Use Nginx Ingress Controller
Now I can get my job done with Option 1 when or why would I choose Option 2 whats the advantage of having nginx with Ingress without Ingress ?
There is a difference between ingress rule (ingress) and ingress controller. So, technically, nginx ingress controller and LoadBalancer type service are not comparable. You can compare ingress resource and LoadBalancer type service, which is below.
Generally speaking:
LoadBalancer type service is a L4(TCP) load balancer. You would use it to expose single app or service to outside world. It would balance the load based on destination IP address and port.
Ingress type resource would create a L7(HTTP/S) load balancer. You would use this to expose several services at the same time, as L7 LB is application aware, so it can determine where to send traffic depending on the application state.
ingress and ingress controller relation:
Ingress, or ingress rules are the rules that ingress controller follows to distribute the load. Ingress controller get the packet, checks ingress rules and determines to which service to deliver the packet.
Nginx Ingress Controller
Nginx ingress controller uses LoadBalancer type service actually as entrypoint to the cluster. Then is checks ingress rules and distributes the load. This can be very confusing. You create an ingress resource, it creates the HTTP/S load balancer. It also gives you an external IP address (on GKE, for example), but when you try hitting that IP address, the connection is refused.
Conclusions:
You would use Loadbalancer type service if you would have a single app, say myapp.com that you want to be mapped to an IP address.
You would use ingress resource if you would have several apps, say myapp1.com, myapp1.com/mypath, myapp2.com, .., myappn.com to be mapped to one IP address.
As the ingress is L7 it is able to distinguish between myapp1.com and myapp1.com/mypath, it is able to route the traffic to the right service.
Accepted answer covered a lots of stuff already. All of the reasons are valid, apart from that the reason I am using ingress controller in aws is to minimize cost. I have multiple web applications which are running in kubernetes cluster aws. To access those applications instead of exposing individual application as LoadBalancer and creating individual ELB (each ELB cost money), I expose ingress controller service as LoadBalancer and created ingress rule for each.
Steps involve:
Ingress service, exposed as loadbalancer which created ELB in aws lets say elb1.aws.com
Ingress rule for each web applications, eg example.com, awesome.com, helloworld.com
Route53 mapping all mapped to same ELB, eg:
example.com -> elb1.aws.com
awesome.com -> elb1.aws.com
helloworld.com -> elb1.aws.com