Kubernetes

If you want to provide extra flags to the kube-apiserver that runs inside minikube how do you do it? You can use the minikube’s --extra-config flag with apiserver.<apiserver flag>=<value>, for e.g. if you want to enable RBAC authorization mode you do it as follows: --extra-config=apiserver.authorization-mode=RBAC So this is a no brainer when doing it for flags whose value can be given right away, like the one above. But what if you want to provide value which is a file path. Because you will have to make that file available for apiserver. And this apiserver runs as a static pod inside minikube. How do you make the file available to that process inside pod inside minikube? ...

A volume mount CVE was discovered in Kubernetes 1.9 and older which allowed access to node file system using emptyDir volume mount using subpath. The official description goes as follows: In Kubernetes versions 1.3.x, 1.4.x, 1.5.x, 1.6.x and prior to versions 1.7.14, 1.8.9 and 1.9.4 containers using subpath volume mounts with any volume type (including non-privileged pods, subject to file permissions) can access files/directories outside of the volume, including the host’s filesystem. ...

NOTE: There is an updated version of this blog here. Few days back I wrote a blog about adding new node to the cluster using the static token file. The problem with that approach is that you need to restart kube-apiserver providing it the path to the token file. Here we will see how to use the bootstrap token, which is very dynamic in nature and can be controlled by using Kubernetes resources like secrets. ...

I enabled PodSecurityPolicy on a minikube cluster by appending PodSecurityPolicy to the apiserver flag in minikube like this: --extra-config=apiserver.enable-admission-plugins=Initializers,NamespaceLifecycle,\ LimitRanger,ServiceAccount,DefaultStorageClass,DefaultTolerationSeconds,\ NodeRestriction,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,\ ResourceQuota,PodSecurityPolicy Ideally when you have PSP enabled and if you don’t define any PSP and authorize it with right RBAC no pod will start in the cluster. But what I saw was that there were some pods still running in kube-system namespace. $ kubectl -n kube-system get pods NAME READY STATUS RESTARTS AGE coredns-576cbf47c7-g2t8v 1/1 Running 4 5d11h etcd-minikube 1/1 Running 2 5d11h heapster-bn5xp 1/1 Running 2 5d11h influxdb-grafana-qzpv4 2/2 Running 4 5d11h kube-addon-manager-minikube 1/1 Running 2 5d11h kube-controller-manager-minikube 1/1 Running 1 4d20h kube-scheduler-minikube 1/1 Running 2 5d11h kubernetes-dashboard-5bb6f7c8c6-9d564 1/1 Running 8 5d11h storage-provisioner 1/1 Running 7 5d11h Which got me thinking what is wrong with the way PSPs work. So if you look closely only two pods are scheduled by a deployment. ...

I passed CKA exam with 92% marks on 19th October 2018. A lot of folks are curious about how to prepare and what resources to follow. Here is my list of things to do and list of resources that might help you on successful CKA exam. The duration of exam is three hours, which is enough time if you do good practice. The exam is pretty straight forward and tests your Kubernetes hands-on knowledge, so whatever you read please try to do it on a real cluster. ...

The setup here is created by following Kubernetes the Hard Way by Kelsey Hightower. So if you are following along in this then do all the setup till the step Bootstrapping the Kubernetes Worker Nodes. In this just don’t start the kubelet, start other services like containerd and kube-proxy. master node Following the docs of TLS Bootstrapping, let’s first create the token authentication file. Create a file with following content: $ cat tokenfile 02b50b05283e98dd0fd71db496ef01e8,kubelet-bootstrap,10001,"system:bootstrappers" You should create the token which is as random as possible by running following command: ...

To setup a multi-node Kubernetes cluster just run this script and you will have a cluster with 3 masters and 3 workers. $ kubectl get nodes -o wide NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME worker-0 Ready <none> 1h v1.11.2 192.168.199.20 <none> Ubuntu 18.04.1 LTS 4.15.0-33-generic cri-o://1.11.2 worker-1 Ready <none> 1h v1.11.2 192.168.199.21 <none> Ubuntu 18.04.1 LTS 4.15.0-33-generic cri-o://1.11.2 worker-2 Ready <none> 1h v1.11.2 192.168.199.22 <none> Ubuntu 18.04.1 LTS 4.15.0-33-generic cri-o://1.11.2 Now to add a new node to this cluster you will need to bring up a VM, for this just use following Vagrantfile. ...