MongoDb 区域副本集 - 每个区域的主节点？

2024-03-01

给定一个具有区域用户（区域为北美、欧洲、亚洲）的应用程序，如何创建允许 HK 用户写入最近节点的副本集？

目标是香港的用户读取和写入其本地节点，而不会遭受写入美国的延迟。我的假设是，我可以在每个区域设置一个应用程序堆栈，通过副本集在所有区域之间共享数据，并且用户可以连接到最近的提供商（全局负载平衡）。

问题是副本集只有一个主节点，并且所有写入都必须发送到该节点。使用辅助和最近的提示读取数据是直接的，但我无法找到写入的解决方案。

这似乎是一个非常可靠的用例，应该处理它，但无法取得任何进展。解决方案、想法、指向某些来源的指针？

感谢@avanti，@MarkusWMalhberg - 思考如何回应这些评论将我推向了正确的方向。这需要一些时间来整合，所以我会稍微详细地解释配置。

Overview

着眼于用户体验，我们希望创建一个 Mongo 数据库配置，允许在最接近用户的位置进行读写。

假设

用户几乎总是在自己的区域中读取和写入文档，并且不介意不频繁读取其他区域的数据是否会较慢。
每个文档都包含一个指示其区域的键（为了简单/清晰）

许多分片文档都重点关注 HA/DR。考虑到用户体验和区域合规性，重点是位置而不是负载分布。

此示例将完全忽略 HA/DR、读取首选项和写入问题，但如果 POC 成熟，则需要解决这些问题。该示例忽略了这些，以便清楚地实现目标：本地读/写。

参考

运营细分 http://docs.mongodb.org/master/core/operational-segregation/?_ga=1.117145798.134938872.1438785509
管理分片标签 http://docs.mongodb.org/master/tutorial/administer-shard-tags/
副本集配置 http://docs.mongodb.org/master/reference/command/replSetGetConfig/#replsetgetconfig-output
不同的 mongos 配置数据库错误 http://docs.mongodb.org/master/tutorial/troubleshoot-sharded-clusters/

Tricks

We know

我们需要一个应用程序数据库，以便所有数据都可用
我们希望用户能够在本地进行读/写，因此我们需要在每个用户组附近建立一个数据库；我们需要一个副本集
写入只能对主副本集节点进行，因此，为了获得每个用户组旁边的主节点，我们需要多个副本；分片集群

在标准 ReplicaSet 和 Sharding 知识中，此配置有 2 个关键点：

为区域本地 ReplicaSet 节点分配优先级，以确保其成为主节点。
使用位置感知分片键标记来确保数据写入本地分片

分片键可以是任何东西：我们只关心用户能够在本地读/写，而不是有效的负载共享。

每个集合都必须进行分片，否则写入将进入分片零。

所需配置

配置

#!/usr/bin/env bash

echo ">>> Clean up processes and files from previous runs"
echo ">>> killAll mongod mongos"
killall mongod mongos

echo ">>> Remove db files and logs"
rm -rf data
rm -rf log

# Create the common log directory
mkdir log

echo ">>> Start replica set for shard US-East"
mkdir -p data/shard-US-East/rsMemberEast data/shard-US-East/rsMemberWest
mongod --replSet shard-US-East --logpath "log/shard-US-East-rsMemberEast.log" --dbpath data/shard-US-East/rsMemberEast --port 37017 --fork --shardsvr --smallfiles
mongod --replSet shard-US-East --logpath "log/shard-US-East-rsMemberWest.log" --dbpath data/shard-US-East/rsMemberWest --port 37018 --fork --shardsvr --smallfiles

echo ">>> Sleep 15s to allow US-East replica set to start"
sleep 15

# The US-East replica set member is assigned priority 2 so that it becomes primary
echo ">>> Configure replica set for shard US-East"
mongo --port 37017 << 'EOF'
config = { _id: "shard-US-East", members:[
         { _id : 0, host : "localhost:37017", priority: 2 },
         { _id : 1, host : "localhost:37018" }]};
rs.initiate(config)
EOF

echo ">>> Start replica set for shard-US-West"
mkdir -p data/shard-US-West/rsMemberEast data/shard-US-West/rsMemberWest
mongod --replSet shard-US-West --logpath "log/shard-US-West-rsMemberEast.log" --dbpath data/shard-US-West/rsMemberEast --port 47017 --fork --shardsvr --smallfiles
mongod --replSet shard-US-West --logpath "log/shard-US-West-rsMemberWest.log" --dbpath data/shard-US-West/rsMemberWest --port 47018 --fork --shardsvr --smallfiles

echo ">>> Sleep 15s to allow US-West replica set to start"
sleep 15

# The US-West replica set member is assigned priority 2 so that it becomes primary
echo ">>> Configure replica set for shard-US-West"
mongo --port 47017 << 'EOF'
config = { _id: "shard-US-West", members:[
         { _id : 0, host : "localhost:47017" },
         { _id : 1, host : "localhost:47018", priority: 2 }]};
rs.initiate(config)
EOF

# Shard config servers: should be 3 and all must be up to deploy a shard cluster
# These are the mongos backing store for routing information
echo ">>> Start config servers"
mkdir -p data/config/config-us-east data/config/config-us-west data/config/config-redundant
mongod --logpath "log/cfg-us-east.log"   --dbpath data/config/config-us-east   --port 57040 --fork --configsvr --smallfiles
mongod --logpath "log/cfg-us-west.log"   --dbpath data/config/config-us-west   --port 57041 --fork --configsvr --smallfiles
mongod --logpath "log/cfg-redundant.log" --dbpath data/config/config-redundant --port 57042 --fork --configsvr --smallfiles

echo ">>> Sleep 5 to allow config servers to start and stabilize"
sleep 5

# All mongos's must point at the same config server, a coordinator dispatches writes to each
echo ">>> Start mongos"
mongos --logpath "log/mongos-us-east.log" --configdb localhost:57040,localhost:57041,localhost:57042 --port 27017 --fork
mongos --logpath "log/mongos-us-west.log" --configdb localhost:57040,localhost:57041,localhost:57042 --port 27018 --fork

echo ">>> Wait 60 seconds for the replica sets to stabilize"
sleep 60

# Enable sharding on the 'sales' database and 'sales.users' collection
# Every collection in 'sales' must be sharded or the writes will go to shard 0
# Add a shard tag so we can associate shard keys with the tag (region)
# Shard tag range main and max cannot be the same so we use a region id for US-East = 1
# and US-West = 2. sh.addTagRange() is inclusive of minKey and exclusive of maxKey.
# We only need to configure one mongos - config will be propogated to all mongos through
# the config server
echo ">>> Add shards to mongos"
mongo --port 27017 <<'EOF'
db.adminCommand( { addshard : "shard-US-East/"+"localhost:37017" } );
db.adminCommand( { addshard : "shard-US-West/"+"localhost:47017" } );

db.adminCommand({enableSharding: "sales"})
db.adminCommand({shardCollection: "sales.users", key: {region:1}});

sh.addShardTag("shard-US-East", "US-East")
sh.addShardTag("shard-US-West", "US-West")
sh.addTagRange("sales.users", { region: 1 }, { region: 2 }, "US-East")
sh.addTagRange("sales.users", { region: 2 }, { region: 3 }, "US-West")
EOF

Testing

验证我们的配置是否正确sh.status()。请注意，分片已正确分配，标签和区域分片键已正确分配。

[starver@rakshasa RegionalSharding 14:38:50]$ mongo --port 27017 sales
...
rakshasa(mongos-3.0.5)[mongos] sales> sh.status()
  sharding version: {
    "_id": 1,
    "minCompatibleVersion": 5,
    "currentVersion": 6,
    "clusterId": ObjectId("55fdddc5746e30dc3651cda4")
  }
  shards:
    {  "_id": "shard-US-East",  "host": "shard-US-East/localhost:37017,localhost:37018",  "tags": [   "US-East" ] }
    {  "_id": "shard-US-West",  "host": "shard-US-West/localhost:47017,localhost:47018",  "tags": [   "US-West" ] }
  balancer:
    Currently enabled:  yes
    Currently running:  no
    Failed balancer rounds in last 5 attempts:  0
    Migration Results for the last 24 hours: 
        1 : Success
  databases:
    {  "_id": "admin",  "partitioned": false,  "primary": "config" }
    {  "_id": "test",  "partitioned": false,  "primary": "shard-US-East" }
    {  "_id": "sales",  "partitioned": true,  "primary": "shard-US-East" }
    sales.users
      shard key: { "region": 1 }
      chunks:
        shard-US-East: 2
        shard-US-West: 1
        { "region": { "$minKey" : 1 } } -> { "region": 1 } on: shard-US-East Timestamp(2, 1) 
        { "region": 1 } -> { "region": 2 } on: shard-US-East Timestamp(1, 3) 
        { "region": 2 } -> { "region": { "$maxKey" : 1 } } on: shard-US-West Timestamp(2, 0) 
        tag: US-East  {
  "region": 1
} -> {
  "region": 2
}
        tag: US-West  {
  "region": 2
} -> {
  "region": 3
}

验证是否对正确的分片和主分片进行了写入。在每个区域创建一条记录

db.users.insert({region:1, name:"us east user"})
db.users.insert({region:2, name:"us west user"})

您可以登录到每个副本集的每个成员，并且仅在美国东部分片上查看东部用户，仅在美国西部分片上查看西部用户。

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