高可用

Last updated 10 months ago

Kubernetes 从 1.5 开始,通过 kops 或者 kube-up.sh 部署的集群会自动部署一个高可用的系统,包括

  • Etcd 集群模式

  • kube-apiserver 负载均衡

  • kube-controller-manager、kube-scheduler 和 cluster-autoscaler 自动选主(有且仅有一个运行实例)

如下图所示

注意:以下步骤假设每台机器上 Kubelet 和 Docker 已配置并处于正常运行状态。

Etcd 集群

安装 cfssl

# On all etcd nodes
curl -o /usr/local/bin/cfssl https://pkg.cfssl.org/R1.2/cfssl_linux-amd64
curl -o /usr/local/bin/cfssljson https://pkg.cfssl.org/R1.2/cfssljson_linux-amd64
chmod +x /usr/local/bin/cfssl*

生成 CA certs:

# SSH etcd0
mkdir -p /etc/kubernetes/pki/etcd
cd /etc/kubernetes/pki/etcd
cat >ca-config.json <<EOF
{
"signing": {
"default": {
"expiry": "43800h"
},
"profiles": {
"server": {
"expiry": "43800h",
"usages": [
"signing",
"key encipherment",
"server auth",
"client auth"
]
},
"client": {
"expiry": "43800h",
"usages": [
"signing",
"key encipherment",
"client auth"
]
},
"peer": {
"expiry": "43800h",
"usages": [
"signing",
"key encipherment",
"server auth",
"client auth"
]
}
}
}
}
EOF
cat >ca-csr.json <<EOF
{
"CN": "etcd",
"key": {
"algo": "rsa",
"size": 2048
}
}
EOF
cfssl gencert -initca ca-csr.json | cfssljson -bare ca -
# generate client certs
cat >client.json <<EOF
{
"CN": "client",
"key": {
"algo": "ecdsa",
"size": 256
}
}
EOF
cfssl gencert -ca=ca.pem -ca-key=ca-key.pem -config=ca-config.json -profile=client client.json | cfssljson -bare client

生成 etcd server/peer certs

# Copy files to other etcd nodes
mkdir -p /etc/kubernetes/pki/etcd
cd /etc/kubernetes/pki/etcd
scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/ca.pem .
scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/ca-key.pem .
scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/client.pem .
scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/client-key.pem .
scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/ca-config.json .
# Run on all etcd nodes
cfssl print-defaults csr > config.json
sed -i '0,/CN/{s/example\.net/'"$PEER_NAME"'/}' config.json
sed -i 's/www\.example\.net/'"$PRIVATE_IP"'/' config.json
sed -i 's/example\.net/'"$PUBLIC_IP"'/' config.json
cfssl gencert -ca=ca.pem -ca-key=ca-key.pem -config=ca-config.json -profile=server config.json | cfssljson -bare server
cfssl gencert -ca=ca.pem -ca-key=ca-key.pem -config=ca-config.json -profile=peer config.json | cfssljson -bare peer

最后运行 etcd,将如下的 yaml 配置写入每台 etcd 节点的 /etc/kubernetes/manifests/etcd.yaml 文件中,注意替换

  • <podname> 为 etcd 节点名称 (比如etcd0, etcd1etcd2

  • <etcd0-ip-address>, <etcd1-ip-address> and <etcd2-ip-address> 为 etcd 节点的内网 IP 地址

cat >/etc/kubernetes/manifests/etcd.yaml <<EOF
apiVersion: v1
kind: Pod
metadata:
labels:
component: etcd
tier: control-plane
name: <podname>
namespace: kube-system
spec:
containers:
- command:
- etcd --name ${PEER_NAME} \
- --data-dir /var/lib/etcd \
- --listen-client-urls https://${PRIVATE_IP}:2379 \
- --advertise-client-urls https://${PRIVATE_IP}:2379 \
- --listen-peer-urls https://${PRIVATE_IP}:2380 \
- --initial-advertise-peer-urls https://${PRIVATE_IP}:2380 \
- --cert-file=/certs/server.pem \
- --key-file=/certs/server-key.pem \
- --client-cert-auth \
- --trusted-ca-file=/certs/ca.pem \
- --peer-cert-file=/certs/peer.pem \
- --peer-key-file=/certs/peer-key.pem \
- --peer-client-cert-auth \
- --peer-trusted-ca-file=/certs/ca.pem \
- --initial-cluster etcd0=https://<etcd0-ip-address>:2380,etcd1=https://<etcd1-ip-address>:2380,etcd1=https://<etcd2-ip-address>:2380 \
- --initial-cluster-token my-etcd-token \
- --initial-cluster-state new
image: gcr.io/google_containers/etcd-amd64:3.1.0
livenessProbe:
httpGet:
path: /health
port: 2379
scheme: HTTP
initialDelaySeconds: 15
timeoutSeconds: 15
name: etcd
env:
- name: PUBLIC_IP
valueFrom:
fieldRef:
fieldPath: status.hostIP
- name: PRIVATE_IP
valueFrom:
fieldRef:
fieldPath: status.podIP
- name: PEER_NAME
valueFrom:
fieldRef:
fieldPath: metadata.name
volumeMounts:
- mountPath: /var/lib/etcd
name: etcd
- mountPath: /certs
name: certs
hostNetwork: true
volumes:
- hostPath:
path: /var/lib/etcd
type: DirectoryOrCreate
name: etcd
- hostPath:
path: /etc/kubernetes/pki/etcd
name: certs
EOF

注意:以上方法需要每个 etcd 节点都运行 kubelet。如果不想使用 kubelet,还可以通过 systemd 的方式来启动 etcd:

export ETCD_VERSION=v3.1.10
curl -sSL https://github.com/coreos/etcd/releases/download/${ETCD_VERSION}/etcd-${ETCD_VERSION}-linux-amd64.tar.gz | tar -xzv --strip-components=1 -C /usr/local/bin/
rm -rf etcd-$ETCD_VERSION-linux-amd64*
touch /etc/etcd.env
echo "PEER_NAME=$PEER_NAME" >> /etc/etcd.env
echo "PRIVATE_IP=$PRIVATE_IP" >> /etc/etcd.env
cat >/etc/systemd/system/etcd.service <<EOF
[Unit]
Description=etcd
Documentation=https://github.com/coreos/etcd
Conflicts=etcd.service
Conflicts=etcd2.service
[Service]
EnvironmentFile=/etc/etcd.env
Type=notify
Restart=always
RestartSec=5s
LimitNOFILE=40000
TimeoutStartSec=0
ExecStart=/usr/local/bin/etcd --name ${PEER_NAME} \
--data-dir /var/lib/etcd \
--listen-client-urls https://${PRIVATE_IP}:2379 \
--advertise-client-urls https://${PRIVATE_IP}:2379 \
--listen-peer-urls https://${PRIVATE_IP}:2380 \
--initial-advertise-peer-urls https://${PRIVATE_IP}:2380 \
--cert-file=/etc/kubernetes/pki/etcd/server.pem \
--key-file=/etc/kubernetes/pki/etcd/server-key.pem \
--client-cert-auth \
--trusted-ca-file=/etc/kubernetes/pki/etcd/ca.pem \
--peer-cert-file=/etc/kubernetes/pki/etcd/peer.pem \
--peer-key-file=/etc/kubernetes/pki/etcd/peer-key.pem \
--peer-client-cert-auth \
--peer-trusted-ca-file=/etc/kubernetes/pki/etcd/ca.pem \
--initial-cluster etcd0=https://<etcd0-ip-address>:2380,etcd1=https://<etcd1-ip-address>:2380,etcd2=https://<etcd2-ip-address>:2380 \
--initial-cluster-token my-etcd-token \
--initial-cluster-state new
[Install]
WantedBy=multi-user.target
EOF
systemctl daemon-reload
systemctl start etcd

kube-apiserver

kube-apiserver.yaml 放到每台 Master 节点的 /etc/kubernetes/manifests/,并把相关的配置放到 /srv/kubernetes/,即可由 kubelet 自动创建并启动 apiserver:

  • basic_auth.csv - basic auth user and password

  • ca.crt - Certificate Authority cert

  • known_tokens.csv - tokens that entities (e.g. the kubelet) can use to talk to the apiserver

  • kubecfg.crt - Client certificate, public key

  • kubecfg.key - Client certificate, private key

  • server.cert - Server certificate, public key

  • server.key - Server certificate, private key

注意:确保 kube-apiserver 配置 --etcd-quorum-read=true(v1.9 之后默认为 true)。

kubeadm

如果使用 kubeadm 来部署集群的话,可以按照如下步骤配置:

# on master0
# deploy master0
cat >config.yaml <<EOF
apiVersion: kubeadm.k8s.io/v1alpha2
kind: MasterConfiguration
kubernetesVersion: v1.11.0
apiServerCertSANs:
- "LOAD_BALANCER_DNS"
api:
controlPlaneEndpoint: "LOAD_BALANCER_DNS:LOAD_BALANCER_PORT"
etcd:
local:
extraArgs:
listen-client-urls: "https://127.0.0.1:2379,https://CP0_IP:2379"
advertise-client-urls: "https://CP0_IP:2379"
listen-peer-urls: "https://CP0_IP:2380"
initial-advertise-peer-urls: "https://CP0_IP:2380"
initial-cluster: "CP0_HOSTNAME=https://CP0_IP:2380"
serverCertSANs:
- CP0_HOSTNAME
- CP0_IP
peerCertSANs:
- CP0_HOSTNAME
- CP0_IP
networking:
# This CIDR is a Calico default. Substitute or remove for your CNI provider.
podSubnet: "192.168.0.0/16"
EOF
kubeadm init --config=config.yaml
# copy TLS certs to other master nodes
CONTROL_PLANE_IPS="10.0.0.7 10.0.0.8"
for host in ${CONTROL_PLANE_IPS}; do
scp /etc/kubernetes/pki/ca.crt "${USER}"@$host:
scp /etc/kubernetes/pki/ca.key "${USER}"@$host:
scp /etc/kubernetes/pki/sa.key "${USER}"@$host:
scp /etc/kubernetes/pki/sa.pub "${USER}"@$host:
scp /etc/kubernetes/pki/front-proxy-ca.crt "${USER}"@$host:
scp /etc/kubernetes/pki/front-proxy-ca.key "${USER}"@$host:
scp /etc/kubernetes/pki/etcd/ca.crt "${USER}"@$host:etcd-ca.crt
scp /etc/kubernetes/pki/etcd/ca.key "${USER}"@$host:etcd-ca.key
scp /etc/kubernetes/admin.conf "${USER}"@$host:
done
# on other master nodes
cat > kubeadm-config.yaml <<EOF
apiVersion: kubeadm.k8s.io/v1alpha2
kind: MasterConfiguration
kubernetesVersion: v1.11.0
apiServerCertSANs:
- "LOAD_BALANCER_DNS"
api:
controlPlaneEndpoint: "LOAD_BALANCER_DNS:LOAD_BALANCER_PORT"
etcd:
local:
extraArgs:
listen-client-urls: "https://127.0.0.1:2379,https://CP1_IP:2379"
advertise-client-urls: "https://CP1_IP:2379"
listen-peer-urls: "https://CP1_IP:2380"
initial-advertise-peer-urls: "https://CP1_IP:2380"
initial-cluster: "CP0_HOSTNAME=https://CP0_IP:2380,CP1_HOSTNAME=https://CP1_IP:2380"
initial-cluster-state: existing
serverCertSANs:
- CP1_HOSTNAME
- CP1_IP
peerCertSANs:
- CP1_HOSTNAME
- CP1_IP
networking:
# This CIDR is a calico default. Substitute or remove for your CNI provider.
podSubnet: "192.168.0.0/16"
EOF
# move files
mkdir -p /etc/kubernetes/pki/etcd
mv /home/${USER}/ca.crt /etc/kubernetes/pki/
mv /home/${USER}/ca.key /etc/kubernetes/pki/
mv /home/${USER}/sa.pub /etc/kubernetes/pki/
mv /home/${USER}/sa.key /etc/kubernetes/pki/
mv /home/${USER}/front-proxy-ca.crt /etc/kubernetes/pki/
mv /home/${USER}/front-proxy-ca.key /etc/kubernetes/pki/
mv /home/${USER}/etcd-ca.crt /etc/kubernetes/pki/etcd/ca.crt
mv /home/${USER}/etcd-ca.key /etc/kubernetes/pki/etcd/ca.key
mv /home/${USER}/admin.conf /etc/kubernetes/admin.conf
# Run the kubeadm phase commands to bootstrap the kubelet:
kubeadm alpha phase certs all --config kubeadm-config.yaml
kubeadm alpha phase kubelet config write-to-disk --config kubeadm-config.yaml
kubeadm alpha phase kubelet write-env-file --config kubeadm-config.yaml
kubeadm alpha phase kubeconfig kubelet --config kubeadm-config.yaml
systemctl start kubelet
# Add the node to etcd cluster
CP0_IP=10.0.0.7
CP0_HOSTNAME=cp0
CP1_IP=10.0.0.8
CP1_HOSTNAME=cp1
KUBECONFIG=/etc/kubernetes/admin.conf kubectl exec -n kube-system etcd-${CP0_HOSTNAME} -- etcdctl --ca-file /etc/kubernetes/pki/etcd/ca.crt --cert-file /etc/kubernetes/pki/etcd/peer.crt --key-file /etc/kubernetes/pki/etcd/peer.key --endpoints=https://${CP0_IP}:2379 member add ${CP1_HOSTNAME} https://${CP1_IP}:2380
kubeadm alpha phase etcd local --config kubeadm-config.yaml
# Deploy the master components
kubeadm alpha phase kubeconfig all --config kubeadm-config.yaml
kubeadm alpha phase controlplane all --config kubeadm-config.yaml
kubeadm alpha phase mark-master --config kubeadm-config.yaml

kube-apiserver 启动后,还需要为它们做负载均衡,可以使用云平台的弹性负载均衡服务或者使用 haproxy/lvs 等为 master 节点配置负载均衡。

kube-controller-manager 和 kube-scheduler

kube-controller manager 和 kube-scheduler 需要保证任何时刻都只有一个实例运行,需要一个选主的过程,所以在启动时要设置 --leader-elect=true,比如

kube-scheduler --master=127.0.0.1:8080 --v=2 --leader-elect=true
kube-controller-manager --master=127.0.0.1:8080 --cluster-cidr=10.245.0.0/16 --allocate-node-cidrs=true --service-account-private-key-file=/srv/kubernetes/server.key --v=2 --leader-elect=true

kube-scheduler.yamlkube-controller-manager.yaml 放到每台 master 节点的 /etc/kubernetes/manifests/ 即可。

kube-dns

kube-dns 可以通过 Deployment 的方式来部署,默认 kubeadm 会自动创建。但在大规模集群的时候,需要放宽资源限制,比如

dns_replicas: 6
dns_cpu_limit: 100m
dns_memory_limit: 512Mi
dns_cpu_requests 70m
dns_memory_requests: 70Mi

另外,也需要给 dnsmasq 增加资源,比如增加缓存大小到 10000,增加并发处理数量 --dns-forward-max=1000 等。

kube-proxy

默认 kube-proxy 使用 iptables 来为 Service 作负载均衡,这在大规模时会产生很大的 Latency,可以考虑使用 IPVS 的替代方式(注意 IPVS 在 v1.9 中还是 beta 状态)。

另外,需要注意配置 kube-proxy 使用 kube-apiserver 负载均衡的 IP 地址:

kubectl get configmap -n kube-system kube-proxy -o yaml > kube-proxy-сm.yaml
sed -i 's#server:.*#server: https://<masterLoadBalancerFQDN>:6443#g' kube-proxy-cm.yaml
kubectl apply -f kube-proxy-cm.yaml --force
# restart all kube-proxy pods to ensure that they load the new configmap
kubectl delete pod -n kube-system -l k8s-app=kube-proxy

kubelet

kubelet 需要配置 kube-apiserver 负载均衡的 IP 地址

sudo sed -i 's#server:.*#server: https://<masterLoadBalancerFQDN>:6443#g' /etc/kubernetes/kubelet.conf
sudo systemctl restart kubelet

数据持久化

除了上面提到的这些配置,持久化存储也是高可用 Kubernetes 集群所必须的。

  • 对于公有云上部署的集群,可以考虑使用云平台提供的持久化存储,比如 aws ebs 或者 gce persistent disk

  • 对于物理机部署的集群,可以考虑使用 iSCSI、NFS、Gluster 或者 Ceph 等网络存储,也可以使用 RAID

参考文档