Etcd

wikipedia:etcd is a distributed key-value store that uses the Raft consensus algorithm to manage a highly-available replicated store, it is used as a software component for software such as CoreOS Container Linux or Kubernetes and for many organizations such as wikipedia

Latency is an important metric as Raft is only as fast as the slowest machine in the majority.

Since etcd’s consensus protocol depends on persistently storing metadata to a log, a majority of etcd cluster members must write every request down to disk

Beside the configuration management, etcd also provides service discovery by allowing deployed applications to announce themselves and the services they offer. Communication with etcd is performed through an exposed REST-based API, which internally uses JSON on top of HTTP; the API may be used directly (through curl or wget, for example), or indirectly throughetcdctl command.

A simple use case is storing database connection details or feature flags in etcd as key-value pairs.

Basic etcd Operation

Adding a new member to the cluster

To add a new server called conf1001.example.com to our cluster, using the etcdctl tool:

etcdctl -C https://etcd1001.example.com:2379 member add conf1001 http://conf1001.example.com:2380
Added member named conf1001 with ID 5f62a924ac85910 to cluster

ETCD_NAME="conf1001"
# Next line is broken down artificially for ease of reading
ETCD_INITIAL_CLUSTER="conf1001=http://conf1001.example.com:2380,
                      etcd1001=http://etcd1001.example.com:2380,
ETCD_INITIAL_CLUSTER_STATE="existing"

etcd ports

TCP Ports 2379 for client communication and on port 2380 for server-to-server communication needs to be open

CKA

• CKA 1.23 Implement etcd backup and restore
• CKA 1.20 Implement etcd backup and restore

Related

• Apache Zookeeper
• kubectl -n kube-system get pod

/etc/kubernetes/pki/etcd/ca.crt 
/etc/kubernetes/pki/etcd/server.crt 
/etc/kubernetes/pki/etcd/server.key
Rancher: https://hub.docker.com/r/rancher/mirrored-coreos-etcd

See also

• etcd, etcdctl, etcdctl snapshot save, etcd versions, etcdHighNumberOfFailedGRPCRequests
• Key-value databases: Berkeley DB, Redis, etcd, leveldb, RocksDB (MyRocks), Infinispan, Amazon DynamoDB, Apache Zookeeper, LevelDB, RocksDB, Pebble

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Source: https://en.wikiversity.org/wiki/DevOps/Etcd