Sharding standalone MongoDB

Question

I've got a standalone MongoDB server with a lot amount of data on it. Let's say, it's srv1 server. I've decided to make a sharded cluster, so I've created additional servers srv2 and srv3.

We have:

• srv1 - existing mongodb server with data, that will be shard0001.
• srv2 - new mongodb server, that will be shard0000.
• srv3 - also new mongodb server, that will be config server with running mongos instance. Mongos instance running only on that server.
• vk - database I want to be sharded.

On srv3 I've started a mongos with --configdb rs0/127.0.0.1:27002 option and a mongod with --replSet rs0 --configsvr --dbpath /data/config --port 27002. After that, via the config instance i've added srv1 and srv2 as a shards with sh.addShard("srv1-2:27017") command. Also, on srv2 I've created an empty database and collections with the same names as on srv1. After that on config server i've executed sh.adminCommand({enableSharding: "vk"}); command.

What I have now:

Surprisingly, it's working. When i'm trying to read/write something to my database, using srv3 as connection point, it's working perfectly! When i've did something before (using srv1 standalone), average response time was about 2 seconds, now it's 0.02 seconds.

The problem I have:

Well, the sharding is not working. Database on srv2 is empty. Here is the output of the db.printShardingStatus() command from srv3:

--- Sharding Status ---
  sharding version: {
        "_id" : 1,
        "minCompatibleVersion" : 5,
        "currentVersion" : 6,
        "clusterId" : ObjectId("5d81f91bdde81f72ac4d1a0a")
  }
  shards:
        {  "_id" : "shard0000",  "host" : "srv2:27017",  "state" : 1 }
        {  "_id" : "shard0001",  "host" : "srv1:27017",  "state" : 1 }
  active mongoses:
        "3.6.3" : 1
  autosplit:
        Currently enabled: yes
  balancer:
        Currently enabled:  yes
        Currently running:  no
        Failed balancer rounds in last 5 attempts:  5
        Last reported error:  Connection refused
        Time of Reported error:  Wed Sep 18 2019 14:41:13 GMT+0200 (CEST)
        Migration Results for the last 24 hours:
                No recent migrations
  databases:
        {  "_id" : "config",  "primary" : "config",  "partitioned" : true }
                config.system.sessions
                        shard key: { "_id" : 1 }
                        unique: false
                        balancing: true
                        chunks:
                                shard0000       1
                        { "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shard0000 Timestamp(1, 0)
        {  "_id" : "shard0000",  "primary" : "shard0000",  "partitioned" : true }
        {  "_id" : "vk",  "primary" : "shard0001",  "partitioned" : true }
        {  "_id" : "vk:",  "primary" : "shard0000",  "partitioned" : true }

Additional info:

The balancer says Connection refused, but i've opened 27017 and 27002 port on every machine in cluster. It's still not working. In mongos (srv3) log there are a lot of successful connections both to srv1 and srv2. Telnet says the same - everything is fine and opened. I've added shards without --replSet options. Mongod instances on srv1 and srv2 working without that options too. I didn't created any chunk keys or something like this.

Thank you for the reading, will be very grateful for any help.

Answer 1

About MongoDB 3.6 shards, from the official release notes:

Starting in 3.6, shards must be replica sets.

When you add shards, should be something like:

sh.addShard( "rs1/mongodb3.example.net:27017,mongodb4.example.net:27017,mongodb5.example.net:27017" )

With a status like:

--- Sharding Status ---
sharding version: {
   "_id" : 1,
   "minCompatibleVersion" : 5,
   "currentVersion" : 6,
   "clusterId" : ObjectId("5be0a488039b1964a7208c60")
}
shards:
   {  "_id" : "rs0",  "host" : "rs0/mongodb0.example.net:27017,mongodb1.example.net:27017,mongodb2.example.net:27017",  "state" : 1 }
   {  "_id" : "rs1",  "host" : "rs1/mongodb3.example.net:27017,mongodb4.example.net:27017,mongodb5.example.net:27017",  "state" : 1 }
active mongoses:
   "3.6.8" : 1