Replica Sets Distributed Across Two or More Data Centers¶
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- Overview
- 一个 从节点 在主数据中心。这个节点需随时准备成为新的主节点。
- Electability of Members
- Connectivity
- Additional Resource
Overview¶
While replica sets provide basic protection against single-instance failure, replica sets whose members are all located in a single data center are susceptible to data center failures. Power outages, network interruptions, and natural disasters are all issues that can affect replica sets whose members are located in a single facility.
Distributing replica set members across geographically distincts data centers adds redundancy and provides fault tolerance if one of the data centers is unavailable.
一个 从节点 在主数据中心。这个节点需随时准备成为新的主节点。¶
To protect your data in case of a data center failure, keep at least one member in an alternate data center. If possible, use an odd number of data centers, and choose a distribution of members that maximizes the likelihood that even with a loss of a data center, the remaining replica set members can form a majority or at minimum, provide a copy of your data.
Examples¶
Three-member Replica Set¶
For example, for a three-member replica set, some possible distributions of members include:
当主节点不可用时，复制集将会选举出一个在 数据中心1 的新的主节点。如果2个数据中心之间无法沟通， 数据中心2 中的节点将不能升职为主节点。
- If Data Center 1 goes down, the replica set becomes read-only.
- If Data Center 2 goes down, the replica set remains writeable as the members in Data Center 1 can hold an election.
- Three data centers: one members to Data Center 1, one member to Data
Center 2, and one member to Data Center 3.
- If any Data Center goes down, the replica set remains writeable as the remaining members can hold an election.
Five-member Replica Set¶
For a replica set with 5 members, some possible distributions of members include:
- Two data centers: three members to Data Center 1 and two members to
Data Center 2.
- If Data Center 1 goes down, the replica set becomes read-only.
- If Data Center 2 goes down, the replica set remains writeable as the members in Data Center 1 can create a majority.
- Three data centers: two member to Data Center 1, two members to Data
Center 2, and one member to site Data Center 3.
- If any Data Center goes down, the replica set remains writeable as the remaining members can hold an election.
For example, the following 5 member replica set distributes its members across three data centers.
Electability of Members¶
Some members of the replica set, such as members that have networking restraint or limited resources, should not be able to become primary in a failover. Configure members that should not become primary to have priority 0.
In some cases, you may prefer that the members in one data center be elected primary before the members in the other data centers. You can modify the priority of the members such that the members in the one data center has higher priority than the members in the other data centers.
In the following example, the replica set members in Data Center 1 have a higher priority than the members in Data Center 2 and 3; the members in Data Center 2 have a higher priority than the member in Data Center 3:
Connectivity¶
Verify that your network configuration allows communication among all members; i.e. each member must be able to connect to every other member.
参见
异地分布式复制集的部署, 部署复制集, 为复制集添加投票节点, and 为复制集新增节点.