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Add a second master node for high availabity in kubernetes

4/17/2018

I was able to follow the documentation and get a kubernetes cluster up. But I would like to add a second master node I tried this on the second node but seeing an error

[root@kubemaster02 ~]# kubeadm init --apiserver-advertise- 
address=10.122.161.XX --pod-network-cidr=10.244.0.0/16 --kubernetes- 
version=v1.10.0
[init] Using Kubernetes version: v1.10.0
[init] Using Authorization modes: [Node RBAC]
[preflight] Running pre-flight checks.
    [WARNING SystemVerification]: docker version is greater than the most 
recently validated version. Docker version: 18.03.0-ce. Max validated 
version: 17.03
    [WARNING FileExisting-crictl]: crictl not found in system path
Suggestion: go get github.com/kubernetes-incubator/cri-tools/cmd/crictl
[preflight] Some fatal errors occurred:
    [ERROR Port-10250]: Port 10250 is in use
[preflight] If you know what you are doing, you can make a check non-fatal 
with `--ignore-preflight-errors=...`

My question is if this is the correct way to add the second master, by doing an init ? another question I have is how to tell if the node is configured as a master or not, the following command is not showing the ROLES for some reason (may be older versions)

[root@master01 ~]# kubectl get nodes -o wide
NAME                   STATUS    AGE       VERSION   EXTERNAL-IP   OS-IMAGE                KERNEL-VERSION
kubemaster01   Ready     215d      v1.8.1    <none>        CentOS Linux 7 (Core)   3.10.0-693.5.2.el7.x86_64
kubemaster02   Ready     132d      v1.8.4    <none>        CentOS Linux 7 (Core)   3.10.0-693.5.2.el7.x86_64
kubenode01     Ready     215d      v1.8.1    <none>        CentOS Linux 7 (Core)   3.10.0-693.5.2.el7.x86_64
kubenode02     Ready     214d      v1.8.1    <none>        CentOS Linux 7 (Core)   3.10.0-693.5.2.el7.x86_64

-- sbolla

kubectl

kubernetes

1 Answer

4/18/2018

In your case, please look what is running on the port 10250 :

netstat -nlp | grep 10250

Because your error is:

[ERROR Port-10250]: Port 10250 is in use

In general, you can bootstrap additional master, and have 2 masters. Before running kubeadm on the other master, you need to first copy the K8s CA cert from kubemaster01. To do this, you have two options:

Option 1: Copy with scp

scp root@<kubemaster01-ip-address>:/etc/kubernetes/pki/* /etc/kubernetes/pki

Option 2: Copy paste

Copy the contents of /etc/kubernetes/pki/ca.crt, /etc/kubernetes/pki/ca.key, /etc/kubernetes/pki/sa.key and /etc/kubernetes/pki/sa.pub and create these files manually on kubemaster02

The next step is to create a Load Balancer that sits in front of your master nodes. How you do this depends on your environment; you could, for example, leverage a cloud provider Load Balancer, or set up your own using NGINX, keepalived, or HAproxy.

For bootstrapping use the config.yaml:

cat >config.yaml <<EOF
apiVersion: kubeadm.k8s.io/v1alpha1
kind: MasterConfiguration
api:
  advertiseAddress: <private-ip>
etcd:
  endpoints:
 - https://<your-ectd-ip>:2379
  caFile: /etc/kubernetes/pki/etcd/ca.pem
  certFile: /etc/kubernetes/pki/etcd/client.pem
  keyFile: /etc/kubernetes/pki/etcd/client-key.pem
networking:
  podSubnet: <podCIDR>
apiServerCertSANs:
- <load-balancer-ip>  
apiServerExtraArgs:
  apiserver-count: "2"
EOF

Ensure that the following placeholders are replaced:

your-ectd-ip the IP address your etcd
private-ip it with the private IPv4 of the master server.
<podCIDR> with your Pod CIDR
load-balancer-ip endpoint to connect your masters

then you can run the command:

kubeadm init --config=config.yaml

and bootstrap the masters.

But if you really want a HA cluster please follow the documentation's minimal requirements and use 3 nodes for masters. They create these requirements for etcd quorum. On every master node they run the etcd which works very close to masters.

-- Nick Rak

Source: StackOverflow

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Add a second master node for high availabity in kubernetes

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