We need to know about pods network isolation.
Is there a possibility to access one pod from another one in cluster? Maybe by namespace dividing?
We also need pod's membership in local networks, which are not accessible from outside.
Any plans? Is it will be soon?
In a standard Kubernetes installation, all pods (even across namespaces) share a flat IP space and can all communicate with each other.
To get isolation, you'll need to customize your install to prevent cross namespace communication. One way to do this is to use OpenContrail. They recently wrote a blog post describing an example deployment using the Guestbook from the Kubernetes repository.
Related
My scenary is like the image below:
After a couple of days trying to find a way to block connections among pods based on a rule i found the Network Policy. But it's not working for me neither at Google Cloud Platform or Local Kubernetes!
My scenary is quite simple, i need a way to block connections among pods based in a rule (e.g. namespace, workload label and so on). At the first glance i tought the will work for me, but i don't know why it's not working at the Google Cloud, even when i create a cluster from the scratch with the option "Network policy" enable.
Network policy will allow you to do exactly what you described on picture. You can allow or block based on labels or namespaces.
It's difficult to help you when you don't explain what you exactly did and what is not working. Update your question with actual network policy YAML you created and ideally also send kubectl get pod --show-labels from the namespace with the pods.
What do you mean by 'local kubernetes' is also unclear but it depends largely on network CNI you're using as it must support network policies. For example Calico or Cilium support it. Minikube in it's default setting don't so you should follow i.e. this guide: https://medium.com/#atsvetkov906090/enable-network-policy-on-minikube-f7e250f09a14
You can use Istio Sidecar to solve this : https://istio.io/latest/docs/reference/config/networking/sidecar/
Another Istio solution is the usage of AuthorizationPolicy : https://istio.io/latest/docs/reference/config/security/authorization-policy/
Just to update because I was involved in the problem of this post.
The problem was with pods that had the istio injected. In this case, all pods in the namespace, because it had istio-injection=enabled.
The NetworkPolicy rule was not taking effect when the selection was made by a matchselector, egress or ingress, and the pods involved were already running before NetworkPolicy was created. By killing the pod and then starting it, the pods that had the label match had access normally. I don't know if there is a way to say to refresh the sidecar inside the pods without having to restart it.
Pods started after the creation of NetworkPolicy did not give the problem of this post.
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.
I am new to the Kubernetes, and I'm trying to understand that how can I apply it for my use-case scenario.
I managed to install a 3-node cluster on VMs within the same network. Searching about K8S's concepts and reading related articles, still I couldn't find answer for my below question. Please let me know if you have knowledge on this:
I've noticed that internal DNS service of K8S applies on the pods and this way services can find each other with hostnames instead of IPs.
Is this applicable for communication between pods of different nodes or this is only within the services inside a single node? (In other words, do we have a dns service on the node level in the K8S, or its only about pods?)
The reason for this question is the scenario that I have in mind:
I need to deploy a micro-service application (written in Java) with K8S. I made docker images from each service in my application and its working locally. Currently, these services are connected via pre-defined IP addresses.
Is there a way to run each of these services within a separate K8S node and use from its DNS service to connect the nodes without pre-defining IPs?
A service serves as an internal endpoint and (depending on the configuration) load balancer to one or several pods behind it. All communication typically is done between services, not between pods. Pods run on nodes, services don't really run anything, they are just routing traffic to the appropriate pods.
A service is a cluster-wide configuration that does not depend on a node, thus you can use a service name in the whole cluster, completely independent from where a pod is located.
So yes, your use case of running pods on different nodes and communicate between service names is a typical setup.
I have deployed a rather large application and I have the need to segregate some of my deployments, which I normally access via cluster ip, into their own dedicated cluster. Once I have done this is there a way I can still allow deployments in cluster a to continue access deployments in cluster b, without exposing them to the internet? These are highly sensitive workloads and exposing them to the internet is not an option.
To reach resources deployed in a Kubernetes cluster from outside, you need to expose those resources. No other ways.
Of course, if you have the Kubernetes clusters in your local network, it is not necessary to expose them to the Internet.
You should be able to use and configure Contiv and Calico in a way that you can have pods in cluster 1 being technically able to talk to pods in cluster 2 without exposing services. Although you also shouldn't forget that this is simply IP based communication and services like e.g. DNS wont be unified right away. So you can't just simple connect by services or pod names.
If I have 10 different services, each of which are independent from each other and run from their own container, can I get kubernetes to run all of those services on, say, 1 host?
This is unclear in the kubernetes documentation. It states that you can force it to schedule containers from the same pod onto one host, using a "multi-container pod", but it doesn't seem to approach the subject of whether you can have multiple pods running on one host.
In fact kubernetes will do exactly what you want by default. It is capable of running dozens if not hundreds of containers on a single host (depending on its specs).
If you want very advanced control over scheduling pods, there is an alpha feature for that, which introduces concept of node/pod (anti)affinities. But I would say it is a rather advanced k8s topic at the moment, so you are probably good with what is in stable/beta for most use cases.
Honorable mention: there is a nasty trick that allows you to control when pods can not be collocated on the same node. An that is when they both declare same hostPort in their ports section. It can be usefull for some cases, but be aware it affects ie. how rolling deployments happen in some situations.
You can use node selectors and assign the same node for each of the pod to the same node / host
http://kubernetes.io/docs/user-guide/node-selection/
Having said that, the whole point to Kubernetes is to manage a cluster where you can deploy apps / pods across them.