Etcd：Kubernetes集群的大脑

Etcd是Kubernetes的关键组件，因为它存储了集群的整个状态：其配置，规格以及运行中的工作负载的状态。在本文中，我们将会揭开其神秘的面纱，了解etcd如何存储所有这些信息。

Etcd 简介

Etcd被定义为分布式，可靠的键值存储，用于分布式系统中最关键的数据。

在Kubernetes世界中，etcd用作服务发现的后端，并存储集群的状态及其配置。

Etcd被部署为一个集群，几个节点的通信由Raft算法处理。在生产环境中，集群包含奇数个节点，并且至少需要三个。在 http://thesecretlivesofdata.com/ 中，您可以找到一个很好的动画，说明该算法的运行方式，它说明了集群生命周期的几个阶段，其中包括：

• 选主
• 日志复制

Kubernetes 中的 Etcd

在Kubernetes集群的上下文中，etcd实例可以作为Pod部署在master节点上（这是我们将在本文中使用的示例）。

为了增加安全性和弹性，还可以将其部署为外部集群。

以下来自Heptio博客的序列图显示了在简单的Pod创建过程中涉及的组件。它很好地说明了API服务器和etcd的交互作用。

Kubernetes 测试集群

在本篇文章中，我们使用的Kubernetes集群，由kubeadm创建的三个节点组成，其中一个master节点运行了Etcd。所选的网络附加组件是weavenet。这种配置不适合实际的HA集群，但足以浏览etcd中存储的数据。

$ kubectl get nodes
NAME    STATUS ROLES  AGE   VERSION
node-01 Ready  master 56m   v1.15.2
node-02 Ready  <none> 2m17  v1.15.2
node-03 Ready  <none> 2m17  v1.15.2

The Etcd Pod

首先，让我们列出集群中运行的所有Pod：

$ kubectl get pods --all-namespaces
NAMESPACE   NAME                           READY STATUS  RESTART AGE
kube-system coredns-5c98db65d4–5kjjv       1/1   Running 0       57m
kube-system coredns-5c98db65d4–88hkq       1/1   Running 0       57m
kube-system etcd-node-01                   1/1   Running 0       56m
kube-system kube-apiserver-node-01         1/1   Running 0       56m
kube-system kube-controller-manager-node-01 1/1  Running 0       56m
kube-system kube-proxy-7642v               1/1   Running 0       3m
kube-system kube-proxy-jsp4r               1/1   Running 0       3m
kube-system kube-proxy-xj8qm               1/1   Running 0       57m
kube-system kube-scheduler-node-01         1/1   Running 0       56m
kube-system weave-net-2hvbx                2/2   Running 0       87s
kube-system weave-net-5mrjl                2/2   Running 0       87s
kube-system weave-net-c76fx                2/2   Running 0       87s

由于集群刚刚被初始化，因此只有kube-system名称空间中的Pod正在运行。这些Pod负责集群的管理任务。我们感兴趣的Pod是 etcd-node-01 ，它运行etcd的实例来负责存储集群的状态。

首先，在etcd Pod中运行一个shell，并检查其中运行的etcd容器的配置：

使用 --advertise-client-urls 标志的值，我们可以使用 etcdctl 实用程序获取所有现有的键/值对，并将其保存在 etcd-kv.json 中。

$ ADVERTISE_URL="https://134.209.178.162:2379"
$ kubectl exec etcd-node-01 -n kube-system -- sh -c 
"ETCDCTL_API=3 etcdctl 
--endpoints $ADVERTISE_URL 
--cacert /etc/kubernetes/pki/etcd/ca.crt 
--key /etc/kubernetes/pki/etcd/server.key 
--cert /etc/kubernetes/pki/etcd/server.crt 
get "" --prefix=true -w json" > etcd-kv.json

快速查看此文件将显示健列表及其对应的值，它们均以base64编码（此处仅显示文件的摘录）。

首先让我们以纯文本格式获取所有键，以查看其内容。我把所有键输出：

$ for k in $(cat etcd-kv.json | jq '.kvs[].key' | cut -d '"' -f2); do echo $k | base64 --decode; echo; done

/registry/apiregistration.k8s.io/apiservices/v1.
/registry/apiregistration.k8s.io/apiservices/v1.apps
/registry/apiregistration.k8s.io/apiservices/v1.authentication.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1.authorization.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1.autoscaling
/registry/apiregistration.k8s.io/apiservices/v1.batch
/registry/apiregistration.k8s.io/apiservices/v1.coordination.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1.networking.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1.rbac.authorization.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1.scheduling.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1.storage.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.admissionregistration.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.apiextensions.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.apps
/registry/apiregistration.k8s.io/apiservices/v1beta1.authentication.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.authorization.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.batch
/registry/apiregistration.k8s.io/apiservices/v1beta1.certificates.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.coordination.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.events.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.extensions
/registry/apiregistration.k8s.io/apiservices/v1beta1.networking.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.node.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.policy
/registry/apiregistration.k8s.io/apiservices/v1beta1.rbac.authorization.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.scheduling.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta1.storage.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1beta2.apps
/registry/apiregistration.k8s.io/apiservices/v2beta1.autoscaling
/registry/apiregistration.k8s.io/apiservices/v2beta2.autoscaling
/registry/certificatesigningrequests/csr-h9mcg
/registry/certificatesigningrequests/csr-qwnxf
/registry/certificatesigningrequests/csr-xklls
/registry/clusterrolebindings/cluster-admin
/registry/clusterrolebindings/kubeadm:kubelet-bootstrap
/registry/clusterrolebindings/kubeadm:node-autoapprove-bootstrap
/registry/clusterrolebindings/kubeadm:node-autoapprove-certificate-rotation
/registry/clusterrolebindings/kubeadm:node-proxier
/registry/clusterrolebindings/system:basic-user
/registry/clusterrolebindings/system:controller:attachdetach-controller
/registry/clusterrolebindings/system:controller:certificate-controller
/registry/clusterrolebindings/system:controller:clusterrole-aggregation-controller
/registry/clusterrolebindings/system:controller:cronjob-controller
/registry/clusterrolebindings/system:controller:daemon-set-controller
/registry/clusterrolebindings/system:controller:deployment-controller
/registry/clusterrolebindings/system:controller:disruption-controller
/registry/clusterrolebindings/system:controller:endpoint-controller
/registry/clusterrolebindings/system:controller:expand-controller
/registry/clusterrolebindings/system:controller:generic-garbage-collector
/registry/clusterrolebindings/system:controller:horizontal-pod-autoscaler
/registry/clusterrolebindings/system:controller:job-controller
/registry/clusterrolebindings/system:controller:namespace-controller
/registry/clusterrolebindings/system:controller:node-controller
/registry/clusterrolebindings/system:controller:persistent-volume-binder
/registry/clusterrolebindings/system:controller:pod-garbage-collector
/registry/clusterrolebindings/system:controller:pv-protection-controller
/registry/clusterrolebindings/system:controller:pvc-protection-controller
/registry/clusterrolebindings/system:controller:replicaset-controller
/registry/clusterrolebindings/system:controller:replication-controller
/registry/clusterrolebindings/system:controller:resourcequota-controller
/registry/clusterrolebindings/system:controller:route-controller
/registry/clusterrolebindings/system:controller:service-account-controller
/registry/clusterrolebindings/system:controller:service-controller
/registry/clusterrolebindings/system:controller:statefulset-controller
/registry/clusterrolebindings/system:controller:ttl-controller
/registry/clusterrolebindings/system:coredns
/registry/clusterrolebindings/system:discovery
/registry/clusterrolebindings/system:kube-controller-manager
/registry/clusterrolebindings/system:kube-dns
/registry/clusterrolebindings/system:kube-scheduler
/registry/clusterrolebindings/system:node
/registry/clusterrolebindings/system:node-proxier
/registry/clusterrolebindings/system:public-info-viewer
/registry/clusterrolebindings/system:volume-scheduler
/registry/clusterrolebindings/weave-net
/registry/clusterroles/admin
/registry/clusterroles/cluster-admin
/registry/clusterroles/edit
/registry/clusterroles/system:aggregate-to-admin
/registry/clusterroles/system:aggregate-to-edit
/registry/clusterroles/system:aggregate-to-view
/registry/clusterroles/system:auth-delegator
/registry/clusterroles/system:basic-user
/registry/clusterroles/system:certificates.k8s.io:certificatesigningrequests:nodeclient
/registry/clusterroles/system:certificates.k8s.io:certificatesigningrequests:selfnodeclient
/registry/clusterroles/system:controller:attachdetach-controller
/registry/clusterroles/system:controller:certificate-controller
/registry/clusterroles/system:controller:clusterrole-aggregation-controller
/registry/clusterroles/system:controller:cronjob-controller
/registry/clusterroles/system:controller:daemon-set-controller
/registry/clusterroles/system:controller:deployment-controller
/registry/clusterroles/system:controller:disruption-controller
/registry/clusterroles/system:controller:endpoint-controller
/registry/clusterroles/system:controller:expand-controller
/registry/clusterroles/system:controller:generic-garbage-collector
/registry/clusterroles/system:controller:horizontal-pod-autoscaler
/registry/clusterroles/system:controller:job-controller
/registry/clusterroles/system:controller:namespace-controller
/registry/clusterroles/system:controller:node-controller
/registry/clusterroles/system:controller:persistent-volume-binder
/registry/clusterroles/system:controller:pod-garbage-collector
/registry/clusterroles/system:controller:pv-protection-controller
/registry/clusterroles/system:controller:pvc-protection-controller
/registry/clusterroles/system:controller:replicaset-controller
/registry/clusterroles/system:controller:replication-controller
/registry/clusterroles/system:controller:resourcequota-controller
/registry/clusterroles/system:controller:route-controller
/registry/clusterroles/system:controller:service-account-controller
/registry/clusterroles/system:controller:service-controller
/registry/clusterroles/system:controller:statefulset-controller
/registry/clusterroles/system:controller:ttl-controller
/registry/clusterroles/system:coredns
/registry/clusterroles/system:csi-external-attacher
/registry/clusterroles/system:csi-external-provisioner
/registry/clusterroles/system:discovery
/registry/clusterroles/system:heapster
/registry/clusterroles/system:kube-aggregator
/registry/clusterroles/system:kube-controller-manager
/registry/clusterroles/system:kube-dns
/registry/clusterroles/system:kube-scheduler
/registry/clusterroles/system:kubelet-api-admin
/registry/clusterroles/system:node
/registry/clusterroles/system:node-bootstrapper
/registry/clusterroles/system:node-problem-detector
/registry/clusterroles/system:node-proxier
/registry/clusterroles/system:persistent-volume-provisioner
/registry/clusterroles/system:public-info-viewer
/registry/clusterroles/system:volume-scheduler
/registry/clusterroles/view
/registry/clusterroles/weave-net
/registry/configmaps/kube-public/cluster-info
/registry/configmaps/kube-system/coredns
/registry/configmaps/kube-system/extension-apiserver-authentication
/registry/configmaps/kube-system/kube-proxy
/registry/configmaps/kube-system/kubeadm-config
/registry/configmaps/kube-system/kubelet-config-1.15
/registry/configmaps/kube-system/weave-net
/registry/controllerrevisions/kube-system/kube-proxy-84c6b844cd
/registry/controllerrevisions/kube-system/weave-net-7db89b6d4
/registry/daemonsets/kube-system/kube-proxy
/registry/daemonsets/kube-system/weave-net
/registry/deployments/kube-system/coredns
/registry/events/default/node-01.15b9e0cd75ea6932
/registry/events/default/node-02.15b9e0ae0342c323
/registry/events/default/node-02.15b9e0ae0f9c2ae3
/registry/events/default/node-02.15b9e0ae0f9c5fa9
/registry/events/default/node-02.15b9e0ae0f9c7206
/registry/events/default/node-02.15b9e0ae1575182e
/registry/events/default/node-02.15b9e0aea1c4eeaf
/registry/events/default/node-02.15b9e0af99ba73a2
/registry/events/default/node-02.15b9e0ca43c5e760
/registry/events/default/node-03.15b9e0ae9bdae96c
/registry/events/default/node-03.15b9e0aea880813c
/registry/events/default/node-03.15b9e0aea880ae05
/registry/events/default/node-03.15b9e0aea880c0de
/registry/events/default/node-03.15b9e0aeb13cfeef
/registry/events/default/node-03.15b9e0afcbcf299b
/registry/events/default/node-03.15b9e0b02f28fa3c
/registry/events/default/node-03.15b9e0cadf7dce89
/registry/events/kube-system/coredns-5c98db65d4-5kjjv.15b9ddb67e6ab700
/registry/events/kube-system/coredns-5c98db65d4-5kjjv.15b9e0af3bdb47fe
/registry/events/kube-system/coredns-5c98db65d4-5kjjv.15b9e0cbbbb7579d
/registry/events/kube-system/coredns-5c98db65d4-5kjjv.15b9e0cc279fbd33
/registry/events/kube-system/coredns-5c98db65d4-5kjjv.15b9e0cc34fb8de2
/registry/events/kube-system/coredns-5c98db65d4-5kjjv.15b9e0cc4994ad54
/registry/events/kube-system/coredns-5c98db65d4-88hkq.15b9ddb6850e5ff1
/registry/events/kube-system/coredns-5c98db65d4-88hkq.15b9e0aea988964f
/registry/events/kube-system/coredns-5c98db65d4-88hkq.15b9e0cbbb3af928
/registry/events/kube-system/coredns-5c98db65d4-88hkq.15b9e0cc2ffb9d11
/registry/events/kube-system/coredns-5c98db65d4-88hkq.15b9e0cc3a4def6c
/registry/events/kube-system/coredns-5c98db65d4-88hkq.15b9e0cc4bd20265
/registry/events/kube-system/coredns-5c98db65d4-88hkq.15b9e0cc6e488534
/registry/events/kube-system/kube-proxy-7642v.15b9e0ae1444b38c
/registry/events/kube-system/kube-proxy-7642v.15b9e0ae7ff6f434
/registry/events/kube-system/kube-proxy-7642v.15b9e0af631fa3d0
/registry/events/kube-system/kube-proxy-7642v.15b9e0af7632698a
/registry/events/kube-system/kube-proxy-7642v.15b9e0af85356aad
/registry/events/kube-system/kube-proxy-jsp4r.15b9e0aeadc2ce3a
/registry/events/kube-system/kube-proxy-jsp4r.15b9e0af27535c1b
/registry/events/kube-system/kube-proxy-jsp4r.15b9e0affc7fc79e
/registry/events/kube-system/kube-proxy-jsp4r.15b9e0b00a290340
/registry/events/kube-system/kube-proxy-jsp4r.15b9e0b01b0a4eef
/registry/events/kube-system/kube-proxy.15b9e0ae1333a730
/registry/events/kube-system/kube-proxy.15b9e0aeaad76df0
/registry/events/kube-system/weave-net-2hvbx.15b9e0c6e9b6c1de
/registry/events/kube-system/weave-net-2hvbx.15b9e0c71a365ad4
/registry/events/kube-system/weave-net-2hvbx.15b9e0c88a5af203
/registry/events/kube-system/weave-net-2hvbx.15b9e0c8a5998774
/registry/events/kube-system/weave-net-2hvbx.15b9e0c8b54252cb
/registry/events/kube-system/weave-net-2hvbx.15b9e0c8b5543df6
/registry/events/kube-system/weave-net-2hvbx.15b9e0c98384d3e1
/registry/events/kube-system/weave-net-2hvbx.15b9e0c9916478ce
/registry/events/kube-system/weave-net-2hvbx.15b9e0c9a090c521
/registry/events/kube-system/weave-net-5mrjl.15b9e0c6e9523ad2
/registry/events/kube-system/weave-net-5mrjl.15b9e0c7194191cb
/registry/events/kube-system/weave-net-5mrjl.15b9e0c89c46497c
/registry/events/kube-system/weave-net-5mrjl.15b9e0c8b335c817
/registry/events/kube-system/weave-net-5mrjl.15b9e0c8c714f12d
/registry/events/kube-system/weave-net-5mrjl.15b9e0c8c770ebdd
/registry/events/kube-system/weave-net-5mrjl.15b9e0c995196184
/registry/events/kube-system/weave-net-5mrjl.15b9e0c9a24d099d
/registry/events/kube-system/weave-net-5mrjl.15b9e0c9b2e0cdef
/registry/events/kube-system/weave-net-c76fx.15b9e0c6ec0133eb
/registry/events/kube-system/weave-net-c76fx.15b9e0c7255593bb
/registry/events/kube-system/weave-net-c76fx.15b9e0c8d4f52821
/registry/events/kube-system/weave-net-c76fx.15b9e0c90ebfeb95
/registry/events/kube-system/weave-net-c76fx.15b9e0c922410c3a
/registry/events/kube-system/weave-net-c76fx.15b9e0c922580ded
/registry/events/kube-system/weave-net-c76fx.15b9e0c9f7834364
/registry/events/kube-system/weave-net-c76fx.15b9e0ca15411664
/registry/events/kube-system/weave-net-c76fx.15b9e0ca2d254f2c
/registry/events/kube-system/weave-net.15b9e0c6e7edf622
/registry/events/kube-system/weave-net.15b9e0c6e9c8d2c1
/registry/events/kube-system/weave-net.15b9e0c6ea880cd2
/registry/leases/kube-node-lease/node-01
/registry/leases/kube-node-lease/node-02
/registry/leases/kube-node-lease/node-03
/registry/masterleases/134.209.178.162
/registry/minions/node-01
/registry/minions/node-02
/registry/minions/node-03
/registry/namespaces/default
/registry/namespaces/kube-node-lease
/registry/namespaces/kube-public
/registry/namespaces/kube-system
/registry/pods/kube-system/coredns-5c98db65d4-5kjjv
/registry/pods/kube-system/coredns-5c98db65d4-88hkq
/registry/pods/kube-system/etcd-node-01
/registry/pods/kube-system/kube-apiserver-node-01
/registry/pods/kube-system/kube-controller-manager-node-01
/registry/pods/kube-system/kube-proxy-7642v
/registry/pods/kube-system/kube-proxy-jsp4r
/registry/pods/kube-system/kube-proxy-xj8qm
/registry/pods/kube-system/kube-scheduler-node-01
/registry/pods/kube-system/weave-net-2hvbx
/registry/pods/kube-system/weave-net-5mrjl
/registry/pods/kube-system/weave-net-c76fx
/registry/priorityclasses/system-cluster-critical
/registry/priorityclasses/system-node-critical
/registry/ranges/serviceips
/registry/ranges/servicenodeports
/registry/replicasets/kube-system/coredns-5c98db65d4
/registry/rolebindings/kube-public/kubeadm:bootstrap-signer-clusterinfo
/registry/rolebindings/kube-public/system:controller:bootstrap-signer
/registry/rolebindings/kube-system/kube-proxy
/registry/rolebindings/kube-system/kubeadm:kubelet-config-1.15
/registry/rolebindings/kube-system/kubeadm:nodes-kubeadm-config
/registry/rolebindings/kube-system/system::extension-apiserver-authentication-reader
/registry/rolebindings/kube-system/system::leader-locking-kube-controller-manager
/registry/rolebindings/kube-system/system::leader-locking-kube-scheduler
/registry/rolebindings/kube-system/system:controller:bootstrap-signer
/registry/rolebindings/kube-system/system:controller:cloud-provider
/registry/rolebindings/kube-system/system:controller:token-cleaner
/registry/rolebindings/kube-system/weave-net
/registry/roles/kube-public/kubeadm:bootstrap-signer-clusterinfo
/registry/roles/kube-public/system:controller:bootstrap-signer
/registry/roles/kube-system/extension-apiserver-authentication-reader
/registry/roles/kube-system/kube-proxy
/registry/roles/kube-system/kubeadm:kubelet-config-1.15
/registry/roles/kube-system/kubeadm:nodes-kubeadm-config
/registry/roles/kube-system/system::leader-locking-kube-controller-manager
/registry/roles/kube-system/system::leader-locking-kube-scheduler
/registry/roles/kube-system/system:controller:bootstrap-signer
/registry/roles/kube-system/system:controller:cloud-provider
/registry/roles/kube-system/system:controller:token-cleaner
/registry/roles/kube-system/weave-net
/registry/secrets/default/default-token-nz988
/registry/secrets/kube-node-lease/default-token-4w7tf
/registry/secrets/kube-public/default-token-pzhnr
/registry/secrets/kube-system/attachdetach-controller-token-69mzv
/registry/secrets/kube-system/bootstrap-signer-token-584pq
/registry/secrets/kube-system/bootstrap-token-w1d2kx
/registry/secrets/kube-system/certificate-controller-token-rff4s
/registry/secrets/kube-system/clusterrole-aggregation-controller-token-6hks4
/registry/secrets/kube-system/coredns-token-b2874
/registry/secrets/kube-system/cronjob-controller-token-55pgx
/registry/secrets/kube-system/daemon-set-controller-token-nhcdf
/registry/secrets/kube-system/default-token-f5kl4
/registry/secrets/kube-system/deployment-controller-token-lm58l
/registry/secrets/kube-system/disruption-controller-token-4tw6s
/registry/secrets/kube-system/endpoint-controller-token-qdh8q
/registry/secrets/kube-system/expand-controller-token-6stw5
/registry/secrets/kube-system/generic-garbage-collector-token-hqfqx
/registry/secrets/kube-system/horizontal-pod-autoscaler-token-h6czj
/registry/secrets/kube-system/job-controller-token-nmw8f
/registry/secrets/kube-system/kube-proxy-token-zcrj8
/registry/secrets/kube-system/namespace-controller-token-trhl9
/registry/secrets/kube-system/node-controller-token-mmf4d
/registry/secrets/kube-system/persistent-volume-binder-token-wnh9s
/registry/secrets/kube-system/pod-garbage-collector-token-h7vvp
/registry/secrets/kube-system/pv-protection-controller-token-lcqb6
/registry/secrets/kube-system/pvc-protection-controller-token-k2kf8
/registry/secrets/kube-system/replicaset-controller-token-zhc7k
/registry/secrets/kube-system/replication-controller-token-l8hr6
/registry/secrets/kube-system/resourcequota-controller-token-bglb2
/registry/secrets/kube-system/service-account-controller-token-5dhxz
/registry/secrets/kube-system/service-controller-token-l98rk
/registry/secrets/kube-system/statefulset-controller-token-dj85r
/registry/secrets/kube-system/token-cleaner-token-qz8hs
/registry/secrets/kube-system/ttl-controller-token-6vbv6
/registry/secrets/kube-system/weave-net-token-87h6x
/registry/serviceaccounts/default/default
/registry/serviceaccounts/kube-node-lease/default
/registry/serviceaccounts/kube-public/default
/registry/serviceaccounts/kube-system/attachdetach-controller
/registry/serviceaccounts/kube-system/bootstrap-signer
/registry/serviceaccounts/kube-system/certificate-controller
/registry/serviceaccounts/kube-system/clusterrole-aggregation-controller
/registry/serviceaccounts/kube-system/coredns
/registry/serviceaccounts/kube-system/cronjob-controller
/registry/serviceaccounts/kube-system/daemon-set-controller
/registry/serviceaccounts/kube-system/default
/registry/serviceaccounts/kube-system/deployment-controller
/registry/serviceaccounts/kube-system/disruption-controller
/registry/serviceaccounts/kube-system/endpoint-controller
/registry/serviceaccounts/kube-system/expand-controller
/registry/serviceaccounts/kube-system/generic-garbage-collector
/registry/serviceaccounts/kube-system/horizontal-pod-autoscaler
/registry/serviceaccounts/kube-system/job-controller
/registry/serviceaccounts/kube-system/kube-proxy
/registry/serviceaccounts/kube-system/namespace-controller
/registry/serviceaccounts/kube-system/node-controller
/registry/serviceaccounts/kube-system/persistent-volume-binder
/registry/serviceaccounts/kube-system/pod-garbage-collector
/registry/serviceaccounts/kube-system/pv-protection-controller
/registry/serviceaccounts/kube-system/pvc-protection-controller
/registry/serviceaccounts/kube-system/replicaset-controller
/registry/serviceaccounts/kube-system/replication-controller
/registry/serviceaccounts/kube-system/resourcequota-controller
/registry/serviceaccounts/kube-system/service-account-controller
/registry/serviceaccounts/kube-system/service-controller
/registry/serviceaccounts/kube-system/statefulset-controller
/registry/serviceaccounts/kube-system/token-cleaner
/registry/serviceaccounts/kube-system/ttl-controller
/registry/serviceaccounts/kube-system/weave-net
/registry/services/endpoints/default/kubernetes
/registry/services/endpoints/kube-system/kube-controller-manager
/registry/services/endpoints/kube-system/kube-dns
/registry/services/endpoints/kube-system/kube-scheduler
/registry/services/specs/default/kubernetes
/registry/services/specs/kube-system/kube-dns
compact_rev_key

上面的结果显示了342个键，这些键定义了集群中所有资源的配置和状态：

• Nodes
• Namespaces
• ServiceAccounts
• Roles and RoleBindings, ClusterRoles / ClusterRoleBindings
• ConfigMaps
• Secrets
• Workloads: Deployments, DaemonSets, Pods, …
• Cluster’s certificates
• The resources within each apiVersion
• The events that bring the cluster in the current state

选择这些键之一后，我们可以使用以下命令获取关联的值：

$ kubectl exec etcd-node-01 -n kube-system —- sh -c 
"ETCDCTL_API=3 etcdctl 
--endpoints $ADVERTISE_URL 
--cacert /etc/kubernetes/pki/etcd/ca.crt 
--key /etc/kubernetes/pki/etcd/server.key 
--cert /etc/kubernetes/pki/etcd/server.crt 
get "KEY" -w json"

例如，让我们获取与 /registry/deployments/kube-system/coredns 键相关联的值：

如果我们解码与此键关联的值，则返回值将很难读，因为无法解释某些字符，但是，当然，Kubernetes知道如何正确处理它们。

根据此结果，我们可以推断出此key用于存储管理coredns Pods的部署的规范和状态。

Pod 的创建

让我们创建一个Pod，并检查如何修改集群的状态以及添加哪些新Key。

$ cat <<EoF | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: www
spec:
  containers:
  - name: nginx
    image: nginx:1.16-alpine
EoF

使用与之前相同的命令，我们获取所有key并将此列表保存在 etcd-kv-after-nginx-pod.json 中。快速比较这两个键列表，一个是在创建集群后立即检索的键（ etcd-kv.json ），另一个是在我们部署了www Pod之后检索的键（ etcd-kv-after-nginx-pod.json ），显示以下内容：

> /registry/events/default/www.15b9e3051648764f
> /registry/events/default/www.15b9e3056b8ce3f0
> /registry/events/default/www.15b9e306918312ea
> /registry/events/default/www.15b9e306a32beb6d
> /registry/events/default/www.15b9e306b5892b60
> /registry/pods/default/www

产生了五个事件和一个Pod，这很有意义。让我们仔细看看，首先解码与事件键关联的值。按照时间顺序，我们可以看到它们与以下操作关联：

default/www 到 node-02
拉取镜像 “nginx:1.16-alpine
成功拉取镜像 “nginx:1.16-alpine
nginx
”Started container nginx

这些事件在描述Pod的命令末尾列出：

$ kubectl describe pod www

最后一个键_ /registry/pods/default/www _，提供与新创建的Pod相关的所有信息：

• 最近的配置
• 相关的token
• I状态

总结

本文的目的不是深入研究etcd，而是稍微解释一下其中包含的内容以及信息的组织方式。这样做是希望它看起来不像黑盒子。

PS: 本文属于翻译， 原文