database replication - Why is an arbiter needed for an election in a primary - secondary - arbiter MongoDB replica set? -
mongo docs list three-member configuration: primary, secondary, arbiter, minimal architecture of replica set.
why arbiter necessary there? if primary fails, secondary won't see heartbeat, needs become primary. in other words, why wouldn't primary + secondary configuration sufficient? related question doesn't seem address issue, discusses larger numbers of nodes.
suppose have 2 servers, 1 primary , 1 secondary.
if secondary can not reach primary server primary downwards (in case secondary should become primary) network issue isolated secondary (this secondary 1 in deed down).
however, if have arbiter , secondary cannot reach primary can reach arbiter issue primary must become new primary. if cannot reach primary, nor arbiter, secondary knows issue is isolated/broken -poor secondary :(- must not become primary
mongodb database-replication
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