在192.168.100.102上关闭shard1复制集的primary节点，测试mongos访问数据依然没有问题，实现了复制集的高可用；

[root@shard1 bin]# mongod -f /usr/local/mongodb/bin/mongodb1.conf --shutdown

killing process with pid: 7140

[root@shard1 bin]# netstat -utpln |grep mon

tcp        0      0 192.168.100.102:27018   0.0.0.0:*               LISTEN      7167/mongod         
tcp        0      0 192.168.100.102:27019   0.0.0.0:*               LISTEN      7194/mongod         
tcp        0      0 192.168.100.102:27025   0.0.0.0:*               LISTEN      7397/mongos  

[root@shard1 bin]# mongo --port 27018 --host 192.168.100.102

MongoDB shell version v3.6.3
connecting to: mongodb://192.168.100.102:27018/
MongoDB server version: 3.6.3
Server has startup warnings: 
2020-04-16T10:37:39.339+0800 I CONTROL  [initandlisten] 
2020-04-16T10:37:39.339+0800 I CONTROL  [initandlisten] ** WARNING: Access control is not enabled for the database.
2020-04-16T10:37:39.339+0800 I CONTROL  [initandlisten] **          Read and write access to data and configuration is unrestricted.
2020-04-16T10:37:39.339+0800 I CONTROL  [initandlisten] ** WARNING: You are running this process as the root user, which is not recommended.
2020-04-16T10:37:39.339+0800 I CONTROL  [initandlisten] 
shard1:PRIMARY> 
Bye

[root@shard1 bin]# mongo --port 27025 --host 192.168.100.102

mongos> show dbs
admin   0.000GB
config  0.001GB
test    0.000GB
zzq     0.003GB
zzq2    0.000GB
zzq7    0.000GB
mongos> use zzq7
switched to db zzq7
mongos> db.hehe.stats()
{
	"sharded" : true,
	"capped" : false,
	"ns" : "zzq7.hehe",
	"count" : 1000,
	"size" : 49000,
	"storageSize" : 40960,
	"totalIndexSize" : 73728,
	"indexSizes" : {
		"_id_" : 32768,
		"id_hashed" : 40960
	},
	"avgObjSize" : 49,
	"nindexes" : 2,
	"nchunks" : 4,
	"shards" : {
		"shard1" : {
			"ns" : "zzq7.hehe",
			"size" : 23520,
			"count" : 480,
			"avgObjSize" : 49,
			"storageSize" : 20480,
			"capped" : false,
			"wiredTiger" : {
				"metadata" : {
					"formatVersion" : 1
				},
....
		"shard2" : {
			"ns" : "zzq7.hehe",
			"size" : 25480,
			"count" : 520,
			"avgObjSize" : 49,
			"storageSize" : 20480,
			"capped" : false,
			"wiredTiger" : {
				"metadata" : {
					"formatVersion" : 1
				},

[root@config ~]# mongo --port 27025 --host 192.168.100.101

mongos> show dbs
admin   0.000GB
config  0.001GB
test    0.000GB
zzq     0.003GB
zzq2    0.000GB
zzq7    0.000GB
mongos> use zzq7
switched to db zzq7
mongos> db.hehe.stats()
{
	"sharded" : true,
	"capped" : false,
	"ns" : "zzq7.hehe",
	"count" : 1000,
	"size" : 49000,
	"storageSize" : 40960,
	"totalIndexSize" : 73728,
	"indexSizes" : {
		"_id_" : 32768,
		"id_hashed" : 40960
	},
	"avgObjSize" : 49,
	"nindexes" : 2,
	"nchunks" : 4,
	"shards" : {
		"shard1" : {
			"ns" : "zzq7.hehe",
			"size" : 23520,
			"count" : 480,
			"avgObjSize" : 49,
			"storageSize" : 20480,
			"capped" : false,
			"wiredTiger" : {
				"metadata" : {
					"formatVersion" : 1
				},
......
		"shard2" : {
			"ns" : "zzq7.hehe",
			"size" : 25480,
			"count" : 520,
			"avgObjSize" : 49,
			"storageSize" : 20480,
			"capped" : false,
			"wiredTiger" : {
				"metadata" : {
					"formatVersion" : 1
				},