The foundation of every SLATE Cluster is a collection of SLATE nodes. Nodes can have a number of different functions, but the two largest roles of a SLATE node are Master and Worker.
A SLATE node can be created on either a virtual machine or physical hardware.
SLATE currently requires CentOS 7 as the base operating system for new clusters. In order to reliably run Kubernetes and connect to the SLATE federation, a few changes are needed to the base CentOS install. The following prerequisite steps will need to be applied to all SLATE nodes in your cluster.
First, you will need to disable SELinux as this generally conflicts with Kubernetes:
setenforce 0 sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux
If you wish to retain the SELinux logging, you can alternatively use ‘permissive’ mode rather than enforcing.
Swap must be disabled for Kubernetes to run effectively. Swap is typically enabled in a default CentOS installation where automatic partitioning has been selected. To disable swap:
swapoff -a sed -e '/swap/s/^/#/g' -i /etc/fstab
In order to properly communicate with other devices within the cluster,
firewalld must be disabled:
systemctl disable --now firewalld
While optional, we strongly recommend disabling root login over SSH for security reasons.
sed -i --follow-symlinks 's/#PermitRootLogin yes/PermitRootLogin no/g' /etc/ssh/sshd_config
Ensure that bridged network traffic goes through iptables.
cat <<EOF > /etc/sysctl.d/k8s.conf net.bridge.bridge-nf-call-ip6tables = 1 net.bridge.bridge-nf-call-iptables = 1 EOF sysctl --system
The SLATE platform uses Kubernetes as its container orchestration system, and Docker as the container run-time. In this section we’ll setup Docker and install the base Kubernetes software components.
We recommend using the Docker Community Edition runtime with Kubernetes and SLATE. It can be installed and activated like so:
# Add Docker stable repo to Yum yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo # Install the latest version of DockerCE and containerd yum install docker-ce docker-ce-cli containerd.io -y # Enable Docker on reboot through systemctl systemctl enable --now docker
The Kubernetes repository can be added to the node in the usual way:
cat <<EOF > /etc/yum.repos.d/kubernetes.repo [kubernetes] name=Kubernetes baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64 enabled=1 gpgcheck=1 repo_gpgcheck=1 gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg EOF
The Kubernetes install includes a few different pieces:
kubeadm is a tool used to bootstrap Kubernetes clusters,
kubectl is the command-line tool needed to interact with and control the cluster, and
kubelet is the system daemon that allows the Kubernetes api to control the cluster nodes. To install and enable these components:
# Install the three necessary Kubernetes components yum install -y kubeadm kubectl kubelet --disableexcludes=kubernetes # Enable Kubelet through systemctl. systemctl enable --now kubelet
At this point the kubelet will be crash-looping as it has no configuration. That is okay for now.
The first node you will add to your cluster will function as the SLATE Cluster Master Node. All possible SLATE topologies will utilize a master node.
To configure a SLATE Master Node, you must first go through the “Operating System Requirements” section above.
We want to initialize our cluster with the pod network CIDR specifically set to 192.168.0.0/16 as this is the default range utilized by the Calico network plugin. If needed, it is possible to set a different RFC1918 range during
kubeadm init and configure Calico to use that range.
kubeadm init --pod-network-cidr=192.168.0.0/16
If you want to permenantly enable kubectl access for the root account you will need to copy the kubernetes admin configuration (KUBECONFIG) to $HOME/.kube/config.
mkdir -p $HOME/.kube sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config sudo chown $(id -u):$(id -g) $HOME/.kube/config
To enable kubeconfig for a single session instead simply run:
In order to enable Pods to communicate with the rest of the cluster, you will need to install a networking plugin. There are a large number of possible networking plugins for Kubernetes. SLATE clusters generally use Calico, although other options should work as well.
To install Calico, you will simply need to apply the appropriate Kubernetes manifest:
kubectl apply -f https://docs.projectcalico.org/v3.8/manifests/calico.yaml
After approximately five minutes, your master node should be ready. You can check with
kubectl get nodes:
[root@your-node ~]# kubectl get nodes NAME STATUS ROLES AGE VERSION your-node.your-domain.edu Ready master 24m v1.16.1
Kubernetes clusters, in order to evenly distribute work across all worker nodes, require a load balancer. There are a few load balancer solutions. We recommend using MetalLB for load balancing on SLATE clusters.
Apply MetalLB to our cluster. This command will create the relevant kubernetes componenents that will run our load balancer.
kubectl apply -f https://raw.githubusercontent.com/google/metallb/v0.8.1/manifests/metallb.yaml
Create the MetalLB configuration and adjust the IP range to reflect your environment. These must be unallocated public IP addresses available to the machine.
cat <<EOF > metallb-config.yaml apiVersion: v1 kind: ConfigMap metadata: namespace: metallb-system name: config data: config: | address-pools: - name: default protocol: layer2 addresses: - 155.101.6.XXX-155.101.6.YYY # Replace this range with whatever IP range your worker nodes may exist in EOF
Finally, create the ConfigMap for MetalLB on your cluster.
kubectl apply -f metallb-config.yaml
To read more about MetalLB installation and configuration, visit their installation instructions.
If your Kubernetes cluster is installed on one or more virtual machines run by OpenStack, there is one small, extra step required to enable MetalLB to route traffic properly.
See the MetalLB documentation for details; in short, OpenStack must be informed that traffic sent to IP addresses controlled by MetalLB has a valid reason to be going to the VMs which make up the Kubernetes cluster.
If you are running a single-node SLATE cluster, you’ll want to remove the “NoSchedule” taint from the Master. This will allow general workloads to run along side of the Kubernetes master node processes. In the case of a dedicated Master and dedicated Workers, please skip to the next section.
To remove the master taint:
kubectl taint nodes --all node-role.kubernetes.io/master-
To distribute work assigned to a SLATE cluster, worker nodes can be networked to a SLATE Master node.
All SLATE Worker nodes should be set up using the “Setting Up a SLATE Node” instructions above.
On your Master node, run the following command to get a full join command for the Master’s cluster:
kubeadm token create --print-join-command
Run this generated join command on the worker node to join it to the cluster.
At this point, you should have a SLATE-Ready Kubernetes cluster. You will now be able to join your cluster to the SLATE Federation.
The SLATE Command Line Interface will let you execute SLATE commands.
On the Master node for your cluster, follow the SLATE CLI installation instructions.
On the Master node for your cluster, execute
slate cluster create [NEW-CLUSTER-NAME] --group [YOUR-GROUP-NAME] --org [YOUR-ORG-NAME] -y
All SLATE clusters should have their geographic locations listed in the cluster’s attributes.
slate cluster update [YOUR-CLUSTER-NAME] --location [LATITUDE],[LONGITUDE]
Cluster administrators can grant cluster access to specific groups.
slate cluster allow-group [YOUR-CLUSTER-NAME] '[GROUP-NAME]'
At this point, you should have a functioning and federated SLATE cluster. If you have any questions on this process, please contact our team for assistance.