My understanding is that if you deploy a Kubernetes service of type 'LoadBalancer' then the Kubernetes cloud controller will automatically provision a Layer 4 load balancer in the cloud you're using. So this would imply that any Kubernetes service of type 'LoadBalancer' always maps to a Layer 4 cloud load balancer, correct?
However, my understanding of the Kubernetes Ingress is that once you deploy your Ingress controllers you also need to provision a service of type 'LoadBalancer' to route traffic to the Ingress controller pods. But this time, since an Ingress is involved, the load balancer will be provisioned as a Layer 7 load balancer and that Layer 7 load balancer sits in front of your Kubernetes cluster and routes traffic to your Ingress controllers.
So it looks like the Kubernetes cloud controller determines whether to provision a Layer 7 or Layer 4 load balancer based on whether an Ingress is present or not. Is this correct?
Ingresses & Ingress-Controller
A Kubernetes service is by default exclusive to the cluster.
Only applications running on the cluster can access them because of this.
An ingress in Kubernetes allows us to direct traffic from outside the cluster to one or more services there.
For all incoming traffic, the ingress typically serves as a single point of entry.
An ingress is assigned a public IP address (provisioned by your cloud provider), making it reachable from outside the cluster.
It then directs all of its traffic to the proper service using a set of rules, however, most Ingress-Controllers directly serve traffic to the pods and not through the service (by constantly checking the endpoint object).
When creating an ingress, there are a few things to consider.
They are initially made to manage web traffic (HTTP or HTTPS).
Although it is possible, using an ingress with other kinds of protocols usually requires additional configuration. Most importantly, the ingress object doesn't actually accomplish anything on its own. Therefore, we must have an ingress controller on hand for an ingress to actually function. Most cloud platforms provide their own ingress controllers, but there are also plenty of open-source options to choose from.
LoadBalancer
Ingresses and LoadBalancers in Kubernetes overlap quite a bit.
This is due to the fact that they are primarily employed to expose services to the internet.
LoadBalancers, however, differ from ingresses in several ways, a load balancer is merely an addition to a service, not a separate entity like an ingress.
For this to work, the cluster must be running on a provider that supports external load balancers. All of the major cloud providers support external load balancers using their own resource types:
AWS uses a Network Load Balancer
GKE also uses a Network Load Balancer
Azure uses a Public Load Balancer
Load balancers can only route to a single service because they are defined per service. As opposed to an ingress, which can route to numerous services within the cluster, this is different. As you've noted, a LoadBalancer operatores on Layer 4 whereas most Ingress Controllers operate on Layer 7; however the Ingress-Controller is usually "exposed" by an external Layer 4 LB to make it accessible in the first place.
That being said, your Cloud-provider doesn't decide wether to create an Ingress or LoadBalancer, it obviously depends on what resource you're creating and your CNI (Container Network Interface), which most Cloud providers also have their own implementation will notify the necessary service to create the resource you want. Also, keep in mind that regardless of the provider, using an external LoadBalancer will typically come with additional costs.
Layer-4 load balancer (or the external load balancer) forwards traffic to Nodeports. It allows you to forward both HTTP and TCP traffic. In Layer 4 Services can be exposed through a single globally managed config-map.
Layer-7 makes smart and informed load balances based on the content of the data,however, layer 4 carries out its load balancing based on its inbuilt software algorithm. Its load balancing is more CPU‑intensive than packet‑based Layer 4 load balancing, but rarely causes degraded performance on a modern server. Layer 7 load balancing enables the load balancer to make smarter load‑balancing decisions, and to apply optimizations and changes to the content.
Some cloud-managed layer-7 load balancers (such as the ALB ingress controller on AWS) expose DNS addresses for ingress rules. You need to map (via CNAME) your domain name to the DNS address generated by the layer-7 load balancer. Google Load Balancer provides a single routable IP address. Nginx Ingress Controller exposes the external IP of all nodes that run the Nginx Ingress Controller. You can configure your own DNS to map (via A records) your domain name to the IP addresses exposed by the Layer-7 load balancer.
Kubernetes Ingress is a collection of routing rules that govern how external users access services running on the Kubernetes cluster. Ingress controller reads the ingress resource’s information and processes the data accordingly. So basically, ingress resources contain the rules to route the traffic and ingress controller routes the traffic.
Routing using ingress is not standardized i.e. different ingress controllers have different semantics (different ways of routing).
At the end of the day, you need to build your own ingress controller based on your requirements and implementations. Ingress is the most flexible and configurable routing feature available.
Please look at the table below for more details :
Related
I used to work with Openshift/OKD cluster deployed in AWS and there it was possible to connect cluster to some domain name from Route53. Then as soon as I was deploying ingress with some hosts mappings (and the hosts defined in ingres were subdomains of the basis domain) all necessary lb rules (Routes in Openshift) and subdomain itself were created by Openshift and were directly available. For example: Openshift is connected to domain "somedomain.com" which is registered in Route53. In ingress I have the host mapping like:
hosts:
- host: sub1.somedomain.com
paths:
- path
After deployment I can reach sub1.somedomain.com. Is this kind of functionality available in GKE?
So far I have seen only mapping to static IP.
Also I red here https://cloud.google.com/kubernetes-engine/docs/how-to/ingress-http2 that if I need to connect service with ingress, the service have to be of type NodePort. Is it realy so? In Openshift it was not required any normal ClusterIP service could be connected to ingress.
Thanks in advance!
I think you should consider the other Ingress Controllers for your use cases.
I'm not an expert of the GKE, but as I can see Best practices for enterprise multi-tenancy as follows,
you need to consider how to route the multiple Ingress hostnames through wildcard subdomain like the OpenShift additionally.
Set up HTTP(S) Load Balancing with Ingress
:
You can create and configure an HTTP(S) load balancer by creating a Kubernetes Ingress resource,
which defines how traffic reaches your Services and how the traffic is routed to your tenant's application.
By registering Services with the Ingress resource, the Services' naming convention becomes consistent,
showing a single ingress, such as tenanta.example.com and tenantb.example.com.
The routing feature depends on the Ingress Controllers basically.
In my finding, the default Ingress Controllers of the GKE just creates a Google Cloud HTTP(S) Load Balancer, but it does not consider multi-tenancy by default like the OpenShift.
In contrast, in the OpenShift, the Ingress Controller was implemented using HAProxy with dynamic configuration feature as follows.
LB -tenanta.example.com--> HAProxy(directly forward the tenanta.example.com traffic to the target pod IPs) ---> Target Pods
The type of service exposition depends on the K8S implementation on each cloud provider.
If the ingress controller is a component inside your cluster, a ClusterIP is enough to have your service reachable (internally from inside the cluster itself)
If the ingress definition configure an external element (in case of GKE, a load balancer), this element isn't a part of the cluster and can't know the ClusterIP (because it is only accessible internally). A node port is required in this case.
So, in your case, either you expose your service in NodePort, or you configure GKE with another Ingress controller, locally installed in the cluster, instead of using this one by default.
So far GKE does not provide the possibility to dynamically create subdomains. The wished situation would be if GKE cluster can be set some DNS zone managed in GCP and there is a mimik of OpenShift Routes using for example ingress annotations.
But the reality tight now - you have to create subdomain or domain youself as well as IP address wich you connect this domain to. And this particular GCP IP address (using name) can be connected to ingress using annotations. Or it can be used in loadbalancer service.
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.
Basically I have Following Hdfs Cluster setup using docker-compose:
Node 1 with IP: 192.168.1.1 having service deployed as below:
Namenode1:9000
HMaster1: 8300
ZooKeeper1:1291
Node 2 with IP: 192.168.1.2 having service deployed as below:
Namenode2:9000
ZooKeeper2:1291
How does Traefik / Ngnix - (Ingress Controllers) forwards request to two different services having configured with same port number?
There are several great tutorials on how ingress and load balancing works in kubernetes, e.g. this one by Mark Betz. As a general rule, it helps to think in terms of services and workloads instead of specific nodes where your workloads are running on.
A workload deployed in Kubernetes (a so called Pod) has its own internal IP address, called a ClusterIP. That pod can have one or more ports open, just on that pod-owned ip address.
If you now have several pods to distribute the load, e.g. like 5 web server processes or backend logic, it would be hard for a client (inside the cluster) to keep track of all those pod IPs, because they also change when a pod is updated or just restarted due to a crash. This is why Kubernetes has a so called concept of services. Those provide a stable DNS name and IP which then transparently "forwards" to one of the healthy pods. So your client only needs to know the DNS name and not keep track of the specific pod IPs.
If you now want to expose such a service to the public, there are different ways. Either you set your service to type: LoadBalancer which then sets up some load balancer infrastructure on your cloud provider and routes traffic to the nodes and then to the pods - or - you already have an ingress controller in place and just define the routing based on host names and paths. An ingress controller itself is such a loadbalanced service with an attached cloud load balancer and also has some pods (with e.g. a traefik or nginx container) which then route your packets accordingly.
So coming back to your initial question: If you want to expose a service with several pods of the same kind, then you would first create a Service resource that matches your Pods using the selector and then you create one single ingress resource that provides a hostname/path and references this service. The ingress controller will pick up those ingress resources and configure the traefik or nginx accordingly. The ingress controller doesn't really care about the host IPs and port numbers, because it acts on the internal kubernetes ClusterIPs, so you even don't need (and shouldn't) expose such a service directly when you have an ingress in place.
I hope this answers your question regarding exposing two workloads over an ingress controller. For details, check the Kubernetes docs on Ingresses. Based on the services you named (zookeeper, hdfs) load balancing and ingresses might not be what you need for that case. Zookeeper instances should be internal in most cases and need to be adressed individually, so you might want to check out headless services, for this use case. Also check the Kubernetes docs for a way to run zookeeper.
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
When using an external load balancer with istio ingress gateways (multiple replicas spread across different nodes), how does it identify which istio ingress gateway it can possibly hit i.e. I can manually access nodeip:nodeport/endpoint for any node manually but how is an external load balancer expected to know all nodes.
Is this manually configured or does the load balancer consume this info from an API
Is there a recommended strategy for bypassing an external load balancer eg. roundrobin across a DNS which is aware of the node ip / port ?
The root of this question is - how do we avoid a single point of failure . Using multiple istio ingress gateway replicas achieves this in istio but then the the external load balancer / load balancer cluster needs to know the replicas . Is this automated or a manual config or is there a single virtual endpoint that the external load balancer hits?
External load balancers are generally configured to do health check on your set of nodes (over /healthz endpoint or some other method), and balance the incoming traffic using an LB algorithm, by sending the packets it receives to one of the healthy nodes over the service's NodePort.
In fact, that's mostly the reason why NodePort type services exist in the first place - they don't have much of an usage by themselves, but they are the intermediate steps between modes LoadBalancer and ClusterIP.
How does the load balancer know about the nodes? It heavily depends on the load balancer. As an example, if you use MetalLB in BGP mode, you need to add your nodes as peers to your external BGP router (either manually or in an automated way). MetalLB takes care of advertising the IPs of the LoadBalancer type services to the router. This means, that router effectively becomes the load balancer of your cluster.
There are also a number of enterprise-grade commercial Kubernetes load balancers out there, such as F5 Big-IP.
Enable ClusterIP for service rather than Node Port. Any LB can be used along with the ingress. But it depends on the platform you are using . It's bare metal or open shift , IBM Cloud, Google cloud. Once the ingress controller ( Metalb, ngnix, Traffic) is able to communicate any LB like F5 GTM or LTM can be set up in front.