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.
Related
In al the tutorials about Kubernetes cluster I have read I didn't see that they mention to 2 load balancers, but only one for the ingress pods.
However, in a proper production environment, should's we have 2 different load balancers?
to balance between the master nodes for requests to the ApiServer.
to balance between the Ingress podes to control the external traffic.
to balance between the master nodes for requests to the ApiServer.
For all production environments its advised to have load
balancer for API Server. This is the first step as part of K8S HA mode creation. More details are in k8s documentation
to balance between the Ingress podes to control the external traffic.
You are correct for this also it’s definitely required to handle external traffic. All the ingress services are created of LoadBalancer Type in their implementations.
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 :
Can anyone please help me understand the ingress traffic flow to a pod in kubernetes? Any web links or documents are much appreciated.
In my application there is a intermittent connection timed out so i want to understand how the traffic is flowing in to cluster and where do i need to enable tcpdump to understand what is happening when there is timeout.
Your question does not contain enough information to give you a detailed answer. There are different types of ingress controllers, and load balancers as well.
So, suppose:
you are using Azure Kubernetes Service
you are using Azure Load Balancer
you have two types of backend pods, each has its own dedicated service
you are using Nginx as ingress controller which is able to do LAYER 7 (OSI) load balancing
Nginx has also its own pods and a service sits in front of these pods. This service has a Service IP which is available only within the AKS cluster. Due to this, additionally you can use Azure Load Balancer (ALB) to make your backend pods available for the public. ALB is a layer 4 load balancer, which sends the incoming traffic to the worker nodes.
Kube-proxy is running on every worker nodes and able to recognize that the traffic from the ALB was destined to the Nginx service.
See the flow on the image below:
Looking at OpenShift HA proxy or Traefik project: https://docs.traefik.io/.
I can see Traefik ingress controller is deployed as a DaemonSet.
It enables to route traffic to correct services/endpoints using virtual host.
Assuming I have a Kubernetes cluster with several nodes.
How can I avoid to have a single point of failure?
Should I have a load balancer (or DNS load balancing), in front of my nodes?
If yes, does it mean that:
Load balancer will send traffic to one node of k8s cluster
Traefik will send the request to one of the endpoint/pods. Where this pod could be located in a different k8s node?
Does it mean there would be a level of indirection?
I am also wondering if the F5 cluster mode feature could avoid such indirection?
EDIT: when used with F5 Ingress resource
You can have a load balancer (BIG IP from F5 or a software load balancer) for traefik pods. When client request comes in it will sent to one of the traefik pods by the load balancer. Once request is in the traefik pod traefik will send the request to IPs of the kubernetes workload pods based on ingress rules by getting the IPs of those pods from kubernetes endpoint API.You can configure L7 load balancing in traefik for your workload pods.
Using a software reverse proxy such as nginx and exposing it via a load balancer introduces an extra network hop from the load balancer to the nginx ingress pod.
Looking at the F5 docs BIG IP controller can also be used as ingress controller and I think using it that way you can avoid the extra hop.
I have a question related to Kubernetes networking.
I have a microservice (say numcruncherpod) running in a pod which is serving requests via port 9000, and I have created a corresponding Service of type NodePort (numcrunchersvc) and node port which this service is exposed is 30900.
My cluster has 3 nodes with following IPs:
192.168.201.70,
192.168.201.71
192.168.201.72
I will be routing the traffic to my cluster via reverse proxy (nginx). As I understand in nginx I need to specify IPs of all these cluster nodes to route the traffic to the cluster, is my understanding correct ?
My worry is since nginx won't have knowledge of cluster it might not be a good judge to decide the cluster node to which the traffic should be sent to. So is there a better way to route the traffic to my kubernetes cluster ?
PS: I am not running the cluster on any cloud platform.
This answer is a little late, and a little long, so I ask for forgiveness before I begin. :)
For people not running kubernetes clusters on Cloud Providers there are 4 distinct options for exposing services running inside the cluster to the world outside.
Service of type: NodePort. This is the simplest and default. Kubernetes assigns a random port to your service. Every node in the cluster listens for traffic to this particular port and then forwards that traffic to any one of the pods backing that service. This is usually handled by kube-proxy, which leverages iptables and load balances using a round-robin strategy. Typically since the UX for this setup is not pretty, people often add an external "proxy" server, such as HAProxy, Nginx or httpd to listen to traffic on a single IP and forward it to one of these backends. This is the setup you, OP, described.
A step up from this would be using a Service of type: ExternalIP. This is identical to the NodePort service, except it also gets kubernetes to add an additional rule on all kubernetes nodes that says "All traffic that arrives for destination IP == must also be forwarded to the pods". This basically allows you to specify any arbitrary IP as the "external IP" for the service. As long as traffic destined for that IP reaches one of the nodes in the cluster, it will be routed to the correct pod. Getting that traffic to any of the nodes however, is your responsibility as the cluster administrator. The advantage here is that you no longer have to run an haproxy/nginx setup, if you specify the IP of one of the physical interfaces of one of your nodes (for example one of your master nodes). Additionally you cut down the number of hops by one.
Service of type: LoadBalancer. This service type brings baremetal clusters at parity with cloud providers. A fully functioning loadbalancer provider is able to select IP from a pre-defined pool, automatically assign it to your service and advertise it to the network, assuming it is configured correctly. This is the most "seamless" experience you'll have when it comes to kubernetes networking on baremetal. Most of LoadBalancer provider implementations use BGP to talk and advertise to an upstream L3 router. Metallb and kube-router are the two FOSS projects that fit this niche.
Kubernetes Ingress. If your requirement is limited to L7 applications, such as REST APIs, HTTP microservices etc. You can setup a single Ingress provider (nginx is one such provider) and then configure ingress resources for all your microservices, instead of service resources. You deploy your ingress provider and make sure it has an externally available and routable IP (you can pin it to a master node, and use the physical interface IP for that node for example). The advantage of using ingress over services is that ingress objects understand HTTP mircoservices natively and you can do smarter health checking, routing and management.
Often people combine one of (1), (2), (3) with (4), since the first 3 are L4 (TCP/UDP) and (4) is L7. So things like URL path/Domain based routing, SSL Termination etc is handled by the ingress provider and the IP lifecycle management and routing is taken care of by the service layer.
For your use case, the ideal setup would involve:
A deployment for your microservice, with health endpoints on your pod
An Ingress provider, so that you can tweak/customize your routing/load-balancing as well as use for SSL termination, domain matching etc.
(optional): Use a LoadBalancer provider to front your Ingress provider, so that you don't have to manually configure your Ingress's networking.
Correct. You can route traffic to any or all of the K8 minions. The K8 network layer will forward to the appropriate minion if necessary.
If you are running only a single pod for example, nginx will most likely round-robin the requests. When the requests hit a minion which does not have the pod running on it, the request will be forwarded to the minion that does have the pod running.
If you run 3 pods, one on each minion, the request will be handled by whatever minion gets the request from nginx.
If you run more than one pod on each minion, the requests will be round-robin to each minion, and then round-robin to each pod on that minion.