Long time I did not come here and I hope you're fine :)
So for now, i have the pleasure of working with kubernetes ! So let's start ! :)
[THE EXISTING]
I have an operationnal kubernetes cluster with which I work every day.it consists of several applications, one of which is of particular interest to us, which is the web management interface.
I currently own one master and four nodes in my cluster.
For my web application, pod contain 3 containers : web / mongo /filebeat, and for technical reasons, we decided to assign 5 users max for each web pod.
[WHAT I WANT]
I want to deploy a web pod on each nodes (web0,web1,web2,web3), what I can already do, and that each session (1 session = 1 user) is distributed as follows:
For now, all HTTP requests are processed by web0.
[QUESTIONS]
Am I forced to go through an external loadbalancer (haproxy)?
Can I use an internal loadbalancer, configuring a service?
Does anyone have experience on the implementation described above?
I thank in advance those who can help me in this process :)
This generally depends how and where you've deployed your Kubernetes infrastructure, but you can do this natively with a few options.
Firstly, you'll need to scale your web deployment. This is very simple to do:
kubectl scale --current-replicas=2 --replicas=3 deployment/web
If you're deployed into a cloud provider (such as AWS using kops, or GKE) you can use a service. Just specify the type as LoadBalancer. Services will spread the sessions for your users.
Another option is to use an Ingress. In order to do this, you'll need to use an Ingress Controller, such as the nginx-ingress-controller which is the most featureful and widely deployed.
Both of these options will automatically loadbalance your incoming application sessions, but they may not necessarily do it in the order you've described in your image, it'll be random across the available web deployments
Related
Recently I have built several microservices within a k8s cluster with Nginx ingress controller and they are working normally.
When dealing with communications among microservices, I attempted gRPC and it worked. Then I discover when microservice A -> gRPC -> microservice B, all requests were only occurred at 1 pod of microservice B (e.g. total 10 pods available for microservice B). In order to load balance the requests to all pods of microservice B, I attempted linkerd and it worked. However, I realized gRPC sometimes will produce internal error (e.g. 1 error out of 100 requests), making me changed to using the k8s DNS way (e.g. my-svc.my-namespace.svc.cluster-domain.example). Then, the requests never fail. I started to hold up gRPC and linkerd.
Later, I was interested in istio. I successfully deployed it to the cluster. However, I observe it always creates its own load balancer, which is not so matching with the existing Nginx ingress controller.
Furthermore, I attempted prometheus and grafana, as well as k9s. These tools let me have better understanding on cpu and memory usage of the pods.
Here I have several questions that I wish to understand:-
If I need to monitor cluster resources, we have prometheus, grafana and k9s. Are they doing the same monitoring role as service mesh (e.g. linkerd, istio)?
if k8s DNS can already achieve load balancing, do we still need service mesh?
if using k8s without service mesh, is it lag behind the normal practice?
Actually I also want to use service mesh every day.
The simple answer is
Service mesh for a kubernetes server is not necessary
Now to answer your questions
If I need to monitor cluster resources, we have prometheus, grafana and k9s. Are they doing the same monitoring role as service mesh (e.g. linkerd, istio)?
K9s is a cli tool that is just a replacement to the kubectl cli tool. It is not a monitor tool. Prometheus and grafana are monitoring tools that will need use the data provided by applications(pods) and builds the time-series data which can be visualized as charts, graphs etc. However the applications have to provide the monitoring data to Prometheus. Service meshes may use a sidecar and provide some default metrics useful for monitoring such as number of requests handled in a second. Your application doesn't need to have any knowledge or implementation of the metrics. Thus service meshes are optional and it offloads the common things such as monitoring or authorization.
if k8s DNS can already achieve load balancing, do we still need service mesh?
Service meshes are not needed for load balancing. When you have multiple services running in the cluster and want to use a single entry point for all your services to simplify maintenance and to save cost, Ingress controllers such as Nginx, Traefik, HAProxy are used. Also, service meshes such as Istio comes with its own ingress controller.
if using k8s without service mesh, is it lag behind the normal practice?
No, there can be clusters that don't have service meshes today and still use Kubernetes.
In the future, Kubernetes may bring some functionalities from service meshes.
Service mesh is not a silver bullet and it doesn't fit into every use case. Service mesh will not do everything for you, it also have bugs and limited features.
You can use Prometheus without Istio and have a very nice app monitoring. Service mesh can simplify some monitoring tasks for you, but it doesn't mean you cannot do it yourself.
Please don't think of DNS as load balancing solution. Kubernetes have Services and Ingresses to do load balancing. Nginx Ingress today is very powerful and have many advanced features.
It heavily depends on your use case.
I am a newbie in Kubernetes.
I have 19 LAN servers with 190 machines.
Each of the 19 LANs has 10 machines and 1 exposed IP.
I have different websites/apps and their environments that are assigned to each LAN.
how do I manage my Kubernetes cluster and do setup/housekeeping.
Would like to have a single portal or manager to manage the websites and environment(dev, QA, prod) and keep isolation.
Is that possible?
I only got a vague idea of what you want to achieve so here goes nothing.
Since Kubernetes has a lot of convenience tools for setting a cluster on a public cloud platform, I'd suggest to start by going through "kubernetes-the-hard-way". It is a guide to setup a cluster on Google Cloud Platform without any additional scripts or tools, but the instructions can be applied to local setup as well.
Once you have an operational cluster, next step should be to setup an Ingress Controller. This gives you the ability to use one or more exposed machines (with public IPs) as gateways for the services running in the cluster. I'd personally recommend Traefik. It has great support for HTTP and Kubernetes.
Once you have the ingress controller setup, your cluster is pretty much ready to use. Process for deploying a service is really specific to service requirements but the right hand rule is to use a Deployment and a Service for stateless loads, and StatefulSet and headless services for stateful workloads that need peer discovery. This is obviously too generalized and have many exceptions.
For managing different environments, you could split your resources into different namespaces.
As for the single portal to manage it all, I don't think that anything as such exists, but I might be wrong. Besides, depending on your workflow, you can create your own portal using the Kubernetes API but it requires a good understanding of Kubernetes itself.
I'm a beginner in Kubernetes and I have a situation as following: I have two differents Pods: PodA and PodB. Firstly, I want to expose PodA to the outside world, so I create a Service (type NodePort or LoadBalancer) for PodA, which is not difficult to understand for me.
Then I want PodA communicate to PodB, and after several hours googling, I found the answer is that I also need to create a Service (type ClusterIP if I want to keep PodB only visible inside the cluster) for PodB, and if I do so, I can let PodA and PodB comminucate to each other. But the problem is I also found this article. According to this webpage, they say that the communication between pods on the same node can be done via cbr0, a Network Bridge, or the communication between pods on different nodes can be done via a route table of the cluster, and they don't mention anything to the Service object (which means we don't need Service object ???).
In fact, I also read the documents of K8s and I found in the Cluster Networking
Cluster Networking
...
2. Pod-to-Pod communications: this is the primary focus of this document.
...
where they also focus on to the Pod-to-Pod communications, but there is no stuff relevant to the Service object.
So, I'm really confusing right now and my question is: Could you please explain to me the connection between these stuff in the article and the Service object? The Service object is a high-level abstract of the cbr0 and route table? And in the end, how can the Pods can communicate to each other?
If I misunderstand something, please, point it out for me, I really appreciate that.
Thank you guys !!!
Motivation behind using a service in a Kubernetes cluster.
Kubernetes Pods are mortal. They are born and when they die, they are not resurrected. If you use a Deployment to run your app, it can create and destroy Pods dynamically.
Each Pod gets its own IP address, however in a Deployment, the set of Pods running in one moment in time could be different from the set of Pods running that application a moment later.
This leads to a problem: if some set of Pods (call them “backends”) provides functionality to other Pods (call them “frontends”) inside your cluster, how do the frontends find out and keep track of which IP address to connect to, so that the frontend can use the backend part of the workload?
That being said, a service is handy when your deployments (podA and podB) are dynamically managed.
Your PodA can always communicate with PodB if it knows the address or the DNS name of PodB. In a cluster environment, there may be multiple replicas of PodB, or an instance of PodB may die and be replaced by another instance with a different address and different name. A Service is an abstraction to deal with this situation. If you use a Service to expose your PodB, then all pods in the cluster can talk to an instance of PodB using that service, which has a fixed name and fixed address no matter how many instances of PodB exists and what their addresses are.
First, I read it as you are dealing with two applications, e.g. ApplicationA and ApplicationB. Don't use the Pod abstraction when you reason about your architecture. On Kubernetes, you are dealing with a distributed system, and it is designed so that you should have multiple instances of your Application, e.g. for High Availability. Each instance of your application is a Pod.
Deploy your applications ApplicationA and ApplicationB as a Deployment resource. Then it is easy do do rolling upgrades without downtime, and Kubernetes will restart any instance of your application if it crash.
For every Deployment or for you, application, create one Service resource, (e.g. ServiceA and ServiceB). When you communicate from ApplicationA to another application, use the Service, e.g. ServiceB. The service will load balance your requests to the instances of the other application, and you can upgrade your Deployment without downtime.
1.Cluster networking : As the name suggests, all the pods deployed in the cluster will be connected by implementing any kubernetes network model like DANM, flannel
Check this link to see how to create a cluster network.
Creating cluster network
With the CNI installed (by implementing cluster network), every pod will get an IP.
2.Service objects created with type ClusterIP, points to the this IPs (via endpoint) created internally to communicate.
Answering your question, Yes, The Service object is a high-level abstract of the cbr0 and route table.
You can use service object to communicate between pods.
You can also implement service mesh like envoy / Istio if the network is complex.
We started using Kubernetes, a few time ago, and now we have deployed a fair amount of services. It's becoming more and more difficult to know exactly what is deployed. I suppose many people are facing the same issue, so is there already a solution to handle this issue?
I'm talking of a solution that when connected to kubernetes (via kubectl for example) can generate a kind of map off the cluster.
In order to display one or many resources you need to use kubectl get command.
To show details of a specific resource or group of resources you can use kubectl describe command.
Please check the links I provided for more details and examples.
You may also want to use Web UI (Dashboard)
Dashboard is a web-based Kubernetes user interface. You can use
Dashboard to deploy containerized applications to a Kubernetes
cluster, troubleshoot your containerized application, and manage the
cluster resources. You can use Dashboard to get an overview of
applications running on your cluster, as well as for creating or
modifying individual Kubernetes resources (such as Deployments, Jobs,
DaemonSets, etc). For example, you can scale a Deployment, initiate a
rolling update, restart a pod or deploy new applications using a
deploy wizard.
Let me know if that helped.
After reading thru Kubernetes documents like this, deployment , service and this I still do not have a clear idea what the purpose of service is.
It seems that the service is used for 2 purposes:
expose the deployment to the outside world (e.g using LoadBalancer),
expose one deployment to another deployment (e.g. using ClusterIP services).
Is this the case? And what about the Ingress?
------ update ------
Connect a Front End to a Back End Using a Service is a good example of the service working with the deployment.
Service
A deployment consists of one or more pods and replicas of pods. Let's say, we have 3 replicas of pods running in a deployment. Now let's assume there is no service. How does other pods in the cluster access these pods? Through IP addresses of these pods. What happens if we say one of the pods goes down. Kunernetes bring up another pod. Now the IP address list of these pods changes and all the other pods need to keep track of the same. The same is the case when there is auto scaling enabled. The number of the pods increases or decreases based on demand. To avoid this problem services come into play. Thus services are basically programs that manages the list of the pods ip for a deployment.
And yes, also regarding the uses that you posted in the question.
Ingress
Ingress is something that is used for providing a single point of entry for the various services in your cluster. Let's take a simple scenario. In your cluster there are two services. One for the web app and another for documentation service. If you are using services alone and not ingress, you need to maintain two load balancers. This might cost more as well. To avoid this, ingress when defined, sits on top of services and routes to services based on the rules and path defined in the ingress.