Editing Etcd

{{lc}}
[[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<ref> https://wikitech.wikimedia.org/wiki/Etcd</ref>

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 through<code>[[etcdctl]]</code> 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 <kbd>conf1001.example.com</kbd> to our cluster, using the <kbd>etcdctl</kbd> tool:
 <syntaxhighlight lang="bash">
$ 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"
</syntaxhighlight>

== etcd ports ==
TCP Ports 2379 for client communication and on port 2380 for server-to-server communication needs to be open <ref>https://github.com/etcd-io/etcd</ref>

== CKA ==
* [[CKA 1.23]] [[Implement etcd backup and restore]]
* [[CKA 1.20]] [[Implement etcd backup and restore]]

== Related ==
* [[Apache Zookeeper]]
* <code>[[kubectl -n kube-system get pod]]</code>
 /etc/kubernetes/pki/etcd/ca.crt 
 /etc/kubernetes/pki/etcd/server.crt 
 /etc/kubernetes/pki/etcd/server.key

== See also ==
* {{etcd}}
* {{K8s}}
* {{Key-value databases}}

{{CC license}}
Source: https://en.wikiversity.org/wiki/DevOps/Etcd

[[Category:Server administration]]
[[Category:Kubernetes]]