由数据结点，投票结点组成，需要配置集群信息，可自动检测集群中的结点健康状态，当有结点出故障时，自动下线和切换主从结点。适用于数据量较大，高可用服务
通常，为了防止单点故障应用程序需要做集群。然而在数据库中除了防止单点故障，还需要做到数据库备份，读写分离，故障转移等。而 MongoDB 的 Replica Set 恰恰都能满足这些要求。
Replica Set角色
Replica Set 的成员是一堆有着同样的数据内容 mongod 的实例集合，包含以下三类角色：
主节点（Primary）
是 Replica Set 中唯一的接收写请求的节点，并将写入指令记录到 oplog 上。副本节点通过复制 oplog 的写入指令同步主节点的数据。Secondary。一个 Replica Set 有且只有Primary 节点，当Primar挂掉后，其他 Secondary 或者 Arbiter 节点会重新选举出来一个主节点。应用程序的默认读取请求也是发到 Primary节点处理的。
副本节点（Secondary）
通过复制主节点 oplog 中的指令与主节点保持同样的数据集，当主节点挂掉的时候，参与主节点选举。
仲裁者（Arbiter）
不存储实际应用数据，只投票参与选取主节点，但不会被选举成为主节点。
复制集架构配置：
架构：
Arbite：127.0.0.1:27017
primary：127.0.0.1:27018
secondary： 127.0.0.1:27019
配置文件内容如下，只要修改logpath、dbpath、pidfilepath和端口即可
arbiter.conf
# syslog配置 logpath=/var/log/mongo/logs/mongod1.log logappend=true timeStampFormat=iso8601-utc # storage 存储配置 dbpath=/data/mongo/repldb1 directoryperdb=true # processManagement 进程管理配置 fork=true # 进程 PID 文件保存目录 pidfilepath=/var/run/mongod1.pid # net 网络配置 bind_ip=127.0.0.1 port=27017 # security 配置 #auth=true # 复制集 replSet=test-set
primary.conf
# syslog配置 logpath=/var/log/mongo/logs/mongod2.log logappend=true timeStampFormat=iso8601-utc # storage 存储配置 dbpath=/data/mongo/repldb2 directoryperdb=true # processManagement 进程管理配置 fork=true # 进程 PID 文件保存目录 pidfilepath=/var/run/mongod2.pid # net 网络配置 bind_ip=127.0.0.1 port=27018 # security 配置 #auth=true # 复制集 replSet=test-set
secondary.conf
# syslog配置 logpath=/var/log/mongo/logs/mongod3.log logappend=true timeStampFormat=iso8601-utc # storage 存储配置 dbpath=/data/mongo/repldb3 directoryperdb=true # processManagement 进程管理配置 fork=true # 进程 PID 文件保存目录 pidfilepath=/var/run/mongod3.pid # net 网络配置 bind_ip=127.0.0.1 port=27019 # security 配置 #auth=true # 复制集 replSet=test-set
分别启动这三个实例：
mongod --config arbiter.conf mongod --config primary.conf mongod --config secondary.conf
初始化：
使用mongodb客户端登陆两个常规节点（primary和secondary）中的任何一个，执行如下命令
mongod 127.0.0.1:27018
登陆后执行初始化命令
> rs.initiate(
... {"_id":"test-set",
... "members":[
... {"_id":1,"host":"127.0.0.1:27018"},
... {"_id":2,"host":"127.0.0.1:27019"}
... ]
... });
{ "ok" : 1 }
test-set:SECONDARY> rs.addArb("127.0.0.1:27017")
{ "ok" : 1 }
查看集群状态：
test-set:PRIMARY> rs.status()
{
"set" : "test-set",
"date" : ISODate("2018-04-19T07:22:22.813Z"),
"myState" : 1,
"term" : NumberLong(1),
"heartbeatIntervalMillis" : NumberLong(2000),
"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1524122535, 1),
"t" : NumberLong(1)
},
"appliedOpTime" : {
"ts" : Timestamp(1524122535, 1),
"t" : NumberLong(1)
},
"durableOpTime" : {
"ts" : Timestamp(1524122535, 1),
"t" : NumberLong(1)
}
},
"members" : [
{
"_id" : 1,
"name" : "127.0.0.1:27018",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 1303,
"optime" : {
"ts" : Timestamp(1524122535, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2018-04-19T07:22:15Z"),
"electionTime" : Timestamp(1524121903, 1),
"electionDate" : ISODate("2018-04-19T07:11:43Z"),
"configVersion" : 2,
"self" : true
},
{
"_id" : 2,
"name" : "127.0.0.1:27019",
"health" : 1,
"state" : 2,
"stateStr" : "SECONDARY",
"uptime" : 649,
"optime" : {
"ts" : Timestamp(1524122535, 1),
"t" : NumberLong(1)
},
"optimeDurable" : {
"ts" : Timestamp(1524122535, 1),
"t" : NumberLong(1)
},
"optimeDate" : ISODate("2018-04-19T07:22:15Z"),
"optimeDurableDate" : ISODate("2018-04-19T07:22:15Z"),
"lastHeartbeat" : ISODate("2018-04-19T07:22:21.472Z"),
"lastHeartbeatRecv" : ISODate("2018-04-19T07:22:21.472Z"),
"pingMs" : NumberLong(0),
"syncingTo" : "127.0.0.1:27018",
"configVersion" : 2
},
{
"_id" : 3,
"name" : "127.0.0.1:27017",
"health" : 1,
"state" : 7,
"stateStr" : "ARBITER",
"uptime" : 69,
"lastHeartbeat" : ISODate("2018-04-19T07:22:21.471Z"),
"lastHeartbeatRecv" : ISODate("2018-04-19T07:22:18.484Z"),
"pingMs" : NumberLong(0),
"configVersion" : 2
}
],
"ok" : 1
}登录127.0.0.1:27019 角色显示为Secondary
mongo 127.0.0.1:27019
2018-04-19T07:00:44.075Z I CONTROL [initandlisten] test-set:SECONDARY> test-set:SECONDARY> test-set:SECONDARY>
在primary上创建数据，测试secondary上是否会同步
test-set:PRIMARY> show dbs
admin 0.000GB
local 0.000GB
test-set:PRIMARY> use testdb
switched to db testdb
test-set:PRIMARY> show collections
test-set:PRIMARY> db.test.insert({"name":"user1"});
WriteResult({ "nInserted" : 1 })登录secondary，查看
test-set:SECONDARY> rs.slaveOk()
test-set:SECONDARY> show dbs
admin 0.000GB
local 0.000GB
testdb 0.000GB
test-set:SECONDARY> use testdb
switched to db testdb
test-set:SECONDARY> show collections
test
test-set:SECONDARY> db.test.find()
{ "_id" : ObjectId("5ad844efa46a748c5a90fe41"), "name" : "user1" }secondary上插入数据报错，说明secondary上没有写的权限
test-set:SECONDARY> db.test.insert({"name":"user2"});
WriteResult({ "writeError" : { "code" : 10107, "errmsg" : "not master" } })验证复制集架构容灾功能
kill掉primary的进程，登录127.0.0.1:27019
test-set:PRIMARY> show dbs
admin 0.000GB
local 0.000GB
testdb 0.000GB
test-set:PRIMARY> rs.status()
{
"set" : "test-set",
"date" : ISODate("2018-04-19T07:44:28.912Z"),
"myState" : 1,
"term" : NumberLong(2),
"heartbeatIntervalMillis" : NumberLong(2000),
"optimes" : {
"lastCommittedOpTime" : {
"ts" : Timestamp(1524123775, 1),
"t" : NumberLong(1)
},
"appliedOpTime" : {
"ts" : Timestamp(1524123862, 1),
"t" : NumberLong(2)
},
"durableOpTime" : {
"ts" : Timestamp(1524123862, 1),
"t" : NumberLong(2)
}
},
"members" : [
{
"_id" : 1,
"name" : "127.0.0.1:27018",
"health" : 0,
"state" : 8,
"stateStr" : "(not reachable/healthy)",
"uptime" : 0,
"optime" : {
"ts" : Timestamp(0, 0),
"t" : NumberLong(-1)
},
"optimeDurable" : {
"ts" : Timestamp(0, 0),
"t" : NumberLong(-1)
},
"optimeDate" : ISODate("1970-01-01T00:00:00Z"),
"optimeDurableDate" : ISODate("1970-01-01T00:00:00Z"),
"lastHeartbeat" : ISODate("2018-04-19T07:44:27.023Z"),
"lastHeartbeatRecv" : ISODate("2018-04-19T07:42:59.830Z"),
"pingMs" : NumberLong(0),
"lastHeartbeatMessage" : "Connection refused",
"configVersion" : -1
},
{
"_id" : 2,
"name" : "127.0.0.1:27019",
"health" : 1,
"state" : 1,
"stateStr" : "PRIMARY",
"uptime" : 2625,
"optime" : {
"ts" : Timestamp(1524123862, 1),
"t" : NumberLong(2)
},
"optimeDate" : ISODate("2018-04-19T07:44:22Z"),
"infoMessage" : "could not find member to sync from",
"electionTime" : Timestamp(1524123790, 1),
"electionDate" : ISODate("2018-04-19T07:43:10Z"),
"configVersion" : 2,
"self" : true
},
{
"_id" : 3,
"name" : "127.0.0.1:27017",
"health" : 1,
"state" : 7,
"stateStr" : "ARBITER",
"uptime" : 1395,
"lastHeartbeat" : ISODate("2018-04-19T07:44:27.009Z"),
"lastHeartbeatRecv" : ISODate("2018-04-19T07:44:28.662Z"),
"pingMs" : NumberLong(0),
"configVersion" : 2
}
],
"ok" : 1
}可以看到127.0.0.1:27018 有一个 "stateStr" : "(not reachable/healthy)"的报错，而127.0.0.1:27019已经变成了primary角色
启动原来的primary.conf配置的实例，角色由原来的primary变成了secondary
test-set:SECONDARY> show dbs
2018-04-19T15:50:04.113+0800 E QUERY [thread1] Error: listDatabases failed:{
"ok" : 0,
"errmsg" : "not master and slaveOk=false",
"code" : 13435,
"codeName" : "NotMasterNoSlaveOk"
} :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
Mongo.prototype.getDBs@src/mongo/shell/mongo.js:62:1
shellHelper.show@src/mongo/shell/utils.js:782:19
shellHelper@src/mongo/shell/utils.js:672:15
@(shellhelp2):1:1
test-set:SECONDARY>其他命令：
rs.slaveOk()：secondary默认不允许读写，执行此命令后，从节点有可读权限
rs.conf()：查看配置情况
test-set:SECONDARY> rs.conf()
{
"_id" : "test-set",
"version" : 2,
"protocolVersion" : NumberLong(1),
"members" : [
{
"_id" : 1,
"host" : "127.0.0.1:27018",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
},
{
"_id" : 2,
"host" : "127.0.0.1:27019",
"arbiterOnly" : false,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
},
{
"_id" : 3,
"host" : "127.0.0.1:27017",
"arbiterOnly" : true,
"buildIndexes" : true,
"hidden" : false,
"priority" : 1,
"tags" : {
},
"slaveDelay" : NumberLong(0),
"votes" : 1
}
],
"settings" : {
"chainingAllowed" : true,
"heartbeatIntervalMillis" : 2000,
"heartbeatTimeoutSecs" : 10,
"electionTimeoutMillis" : 10000,
"catchUpTimeoutMillis" : 60000,
"getLastErrorModes" : {
},
"getLastErrorDefaults" : {
"w" : 1,
"wtimeout" : 0
},
"replicaSetId" : ObjectId("5ad841247ffb05dbb6b4a13b")
}
}原文地址：http://blog.51cto.com/zengestudy/2105414
