Election process in Replica sets

In this blog, we will understand the election process in replica sets.

• If the PRIMARY node is down, Replica sets, use election process to determine which member will become a PRIMARY node.
  PS: You can make the PRIMARY node inactive by using this command

rs.stepDown()

If you specify a non-numeric value in the parameter, the command uses 60 seconds as default.

• The median time before a cluster elects a new primary should not typically exceed 12 seconds.
• a replica set can have up to 50 members, out of which it can have a max of 7 voting members and a max of 43
  non-voting members.

• Members can vote or cannot vote, depending on the votes field value that is set.

rs.conf().members[x].votes = 1; // member can vote
rs.conf().members[x].votes = 0; // member cannot vote

• Members can or cannot become a PRIMARY node, depending on the priority field value that is set.

rs.conf().members[x].priority = 1; // member can become PRIMARY
rs.conf().members[x].priority = 0; // member cannot become PRIMARY

Voting Members:

• Voting members can participate in the election process and can become a PRIMARY node and must have a priority of > 0.
• Only voting members with priority > 0 must be in PRIMARY, SECONDARY, STARTUP2, RECOVERING, ARBITER, ROLLBACK states to participate in the elections.

Please refer to this link for complete details about the Replica Member states.

• You can type the below command and it should be in the above-mentioned state.

>rs.conf().members
//this command is entered on PRIMARY node
{
 "_id" : 0,
 "host" : "localhost:27018",
 "arbiterOnly" : false,
 "buildIndexes" : true,
 "hidden" : false,
 "priority" : 1,
 "tags" : {
  
 },
 "slaveDelay" : NumberLong(0),
 "votes" : 1
}

You can see priority: 1 and votes: 1

Non Voting Members:

• Non-voting members cannot participate in the election process and can't become a PRIMARY node and must have a priority of 0.
• Although non-voting members do not vote in elections, these members hold copies of the replica set’s data and can accept read operations from client applications.
  They will have priority: 0 and votes: 0

Please refer to this link, on how different ways to configure SECONDARY nodes

Thank You…