Priority 0 Replica Set Members

On this page

• Priority 0 Members as Standbys
• Priority 0 Members and Failover
• Configuration

Apriority 0_member is a secondary thatcannotbecomeprimary._Priority 0_members cannot_triggerelections. Otherwise these members function as normal secondaries. A_priority 0_member maintains a copy of the data set, accepts read operations, and votes in elections. Configure a_priority 0_member to preventsecondariesfrom becoming primary, which is particularly useful in multi-data center deployments.

For example, in the following diagram, one data center hosts the primary and a secondary. A second data center hosts one_priority 0_member that cannot become primary.

Priority 0 Members as Standbys

A_priority 0_member can function as a standby. In some replica sets, it might not be possible to add a new member in a reasonable amount of time. A standby member keeps a current copy of the data to be able to replace an unavailable member.

In many cases, you need not set standby topriority 0. However, in sets with varied hardware orgeographic distribution, a_priority 0_standby ensures that only qualified members become primary.

A_priority 0_standby may also be valuable for some members of a set with different hardware or workload profiles. In these cases, deploy a member with_priority 0_so it can’t become primary. Also consider using anhidden memberfor this purpose.

If your set already has seven voting members, also configure the member asnon-voting.

Priority 0 Members and Failover

When configuring a_priority 0_member, consider potential failover patterns, including all possible network partitions. Always ensure that your main data center contains both a quorum of voting members and contains members that are eligible to be primary.

Configuration

To configure a_priority 0_member, seePrevent Secondary from Becoming Primary.