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Explore ETCD

What is ETCD

https://etcd.io/

  • A distributed key-value data store which stores the state of the system and objects
  • Use Raft protocol to coordinate the data access in distributed setup
  • You can influence the way the API Server is using etcd via a number of options at start-up time. --etcd-servers List of etcd servers to connect with (scheme://ip:port)
  • Kubernetes stores its objects in etcd either as a JSON string or in Protocol Buffers(“protobuf” for short) format

Flow from kubectl apply -f pod.yaml to object in etcd

  • Get the version from http path (e.g. v1 or v1beta1)
  • Create the empty object using Scheme in the right version
  • JSON or protobuf decoder converts the payload into object
  • Write requests are all applied to ETCD leader node

flow

Flow from kubectl get pods

  • Get request is sent to kube-apiserver
  • kube-apiserver uses the ETCD client lib to talk to etcd cluster. Implementation
  • ETCD3 client performs a quorum read by default to make sure always the latest value gets returned. ETCD2 needs to pass in a flag quorum-read=true to achieve the quorum read

Lab

  • Using footloose to build the vm-like clusters
  • Using Ansible to configure the clusters
    • Install pre requisites
    • Install etcd
  • Bring up a kind cluster using the external etcd cluster

References