e196a0e8d2
This commit adds a document that provides tips of how to use the go client library. Currently it describes how to use the client.SelectionMode parameter that is added in https://github.com/coreos/etcd/pull/4030.
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etcd go client API
This document describes using the etcd client Go package github.com/coreos/etcd/client.
Endpoint Selection Mode
Programs call client.New() to create an etcd client instance, passing configuration through the client.Config parameter. client.Config's SelectionMode member is an EndpointSelectionMode enum that specifies the policy for choosing the etcd cluster node to which requests are sent.
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EndpointSelectionRandom (default)
The default value of the SelectionMode is EndpointSelectionRandom. As the name implies, the client object will pick a node from the members of the cluster in a random fashion. If the cluster has three members, A, B, and C, the client picks any node from its three members as its request destination.
EndpointSelectionPrioritizeLeader
If SelectionMode is set to EndpointSelectionPrioritizeLeader, requests are sent directly to the cluster leader. This reduces forwarding roundtrips compared to making requests to etcd followers who then forward them to the cluster leader. In the event of a leader failure, however, clients configured this way cannot prioritize among the remaining etcd followers. Therefore, when a client sets SelectionMode to EndpointSelectionPrioritizeLeader, it must use client.AutoSync() to maintain its knowledge of current cluster state.