##Deploying a sharded MongoDB(3.2+) cluster with Ansible(2.1+)

• Requires Ansible 2.1+
• Expects CentOS/RHEL 7 hosts

Rewrite from ansible mongodb example with mongodb3.2, ansible2.1, CentOS 7.

The diagram above illustrates the deployment model for a MongoDB cluster deployed by Ansible. This deployment model focuses on deploying three shard servers, each having a replica set, with the backup replica servers serving as the other two shard primaries. The configuration servers are co-located with the shards. The mongos servers are best deployed on seperate servers. This is the minimum recomended configuration for a production-grade MongoDB deployment. Please note that the playbooks are capable of deploying N node clusters, not limited to three. Also, all the processes are secured using keyfiles.

Deployment Example

---

The inventory file looks as follows:

	#The site wide list of mongodb servers
	[mongo_servers]
	mongo1 mongod_port=2700
	mongo2 mongod_port=2701
	mongo3 mongod_port=2702

	#The list of servers where replication should happen, including the master server.
	[replication_servers]
	mongo3
	mongo1
	mongo2

	#The list of mongodb configuration servers, make sure it is 1 or 3
	[mongoc_servers]
	mongo1
	mongo2
	mongo3

	#The list of servers where mongos servers would run. 
	[mongos_servers]
	mongos1
	mongos2

Build the site by mongodb playbook using the following command:

	ansible-playbook -i hosts site.yml

Build the site by vagrant ansible provision using the following command:

	vagrant up		

Verifying the Deployment

---

Once configuration and deployment has completed we can check replication set availability by connecting to individual primary replication set nodes. Run vagrant ssh mongo1 to login then exec mongo localhost/admin -u admin -p 123456 and issue the command to query the status of replication set, we should get a similar output.

mongos> sh.status()
--- Sharding Status --- 
  sharding version: {
    "_id" : 1,
    "minCompatibleVersion" : 5,
    "currentVersion" : 6,
    "clusterId" : ObjectId("586e54fa29837f51186882a2")
}
  shards:
    {  "_id" : "mongo1",  "host" : "mongo1/mongo1:2700,mongo2:2700,mongo3:2700" }
    {  "_id" : "mongo2",  "host" : "mongo2/mongo1:2701,mongo2:2701,mongo3:2701" }
    {  "_id" : "mongo3",  "host" : "mongo3/mongo1:2702,mongo2:2702,mongo3:2702" }
  active mongoses:
    "3.2.11" : 2
  balancer:
    Currently enabled:  yes
    Currently running:  no
    Failed balancer rounds in last 5 attempts:  0
    Migration Results for the last 24 hours: 
        4 : Success
  databases:
    {  "_id" : "test",  "primary" : "mongo2",  "partitioned" : true }
        test.messages
            shard key: { "createTime" : 1 }
            unique: false
            balancing: true
            chunks:
                mongo1	1
                mongo2	1
                mongo3	1
            { "createTime" : { "$minKey" : 1 } } -->> { "createTime" : ISODate("0381-01-05T14:15:47.299Z") } on : mongo1 Timestamp(2, 0) 
            { "createTime" : ISODate("0381-01-05T14:15:47.299Z") } -->> { "createTime" : ISODate("2584-01-05T14:15:47.299Z") } on : mongo3 Timestamp(3, 0) 
            { "createTime" : ISODate("2584-01-05T14:15:47.299Z") } -->> { "createTime" : { "$maxKey" : 1 } } on : mongo2 Timestamp(3, 1) 
        test.user
            shard key: { "_id" : "hashed" }
            unique: false
            balancing: true
            chunks:
                mongo1	2
                mongo2	2
                mongo3	2
            { "_id" : { "$minKey" : 1 } } -->> { "_id" : NumberLong("-6148914691236517204") } on : mongo1 Timestamp(3, 2) 
            { "_id" : NumberLong("-6148914691236517204") } -->> { "_id" : NumberLong("-3074457345618258602") } on : mongo1 Timestamp(3, 3) 
            { "_id" : NumberLong("-3074457345618258602") } -->> { "_id" : NumberLong(0) } on : mongo2 Timestamp(3, 4) 
            { "_id" : NumberLong(0) } -->> { "_id" : NumberLong("3074457345618258602") } on : mongo2 Timestamp(3, 5) 
            { "_id" : NumberLong("3074457345618258602") } -->> { "_id" : NumberLong("6148914691236517204") } on : mongo3 Timestamp(3, 6) 
            { "_id" : NumberLong("6148914691236517204") } -->> { "_id" : { "$maxKey" : 1 } } on : mongo3 Timestamp(3, 7) 

We can check the status of the shards as follows: connect to the mongos service mongo localhost/test -u admin -p 123456 and issue the following command to get the status of the Shards:

mongos> db.user.find({_id: 1 }).explain()
{
    "queryPlanner" : {
        "mongosPlannerVersion" : 1,
        "winningPlan" : {
            "stage" : "SINGLE_SHARD",
            "shards" : [
                {
                    "shardName" : "mongo3",
                    "connectionString" : "mongo3/mongo1:2702,mongo2:2702,mongo3:2702",
                    "serverInfo" : {
                        "host" : "mongo3",
                        "port" : 2702,
                        "version" : "3.2.11",
                        "gitVersion" : "009580ad490190ba33d1c6253ebd8d91808923e4"
                    },
                    "plannerVersion" : 1,
                    "namespace" : "test.user",
                    "indexFilterSet" : false,
                    "parsedQuery" : {
                        "_id" : {
                            "$eq" : 1
                        }
                    },
                    "winningPlan" : {
                        "stage" : "SHARDING_FILTER",
                        "inputStage" : {
                            "stage" : "IDHACK"
                        }
                    },
                    "rejectedPlans" : [ ]
                }
            ]
        }
    },
    "ok" : 1
}