MongoDB error when sharding a collection: ns not found - mongodb

Question

I've setup a simple server configuration for testing sharding functionnalities purpose and i get the error above.
My configuration is pretty simple: one config server, one shard server and one mongos (respectively in 127.0.0.1:27019, 127.0.0.1:27018, 127.0.0.1:27017).
Everything looks to work well until i try to shard a collection, the command gives me the following:
sh.shardCollection("test.test", { "test" : 1 } )
{
"ok" : 0,
"errmsg" : "ns not found",
"code" : 26,
"codeName" : "NamespaceNotFound",
"operationTime" : Timestamp(1590244259, 5),
"$clusterTime" : {
"clusterTime" : Timestamp(1590244259, 5),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
}
}
The config server and shard server outputs show no errors:
2020-05-23T10:39:46.629-0400 I SHARDING [conn11] about to log metadata event into changelog: { _id: "florent-Nitro-AN515-53:27018-2020-05-23T10:39:46.629-0400-5ec935b2bec982e313743b1a", server: "florent-Nitro-AN515-53:27018", shard: "rs0", clientAddr: "127.0.0.1:58242", time: new Date(1590244786629), what: "shardCollection.start", ns: "test.test", details: { shardKey: { test: 1.0 }, collection: "test.test", uuid: UUID("152add6f-e56b-40c4-954c-378920eceede"), empty: false, fromMapReduce: false, primary: "rs0:rs0/127.0.0.1:27018", numChunks: 1 } }
2020-05-23T10:39:46.620-0400 I SHARDING [conn25] distributed lock 'test' acquired for 'shardCollection', ts : 5ec935b235505bcc59eb60c5
2020-05-23T10:39:46.622-0400 I SHARDING [conn25] distributed lock 'test.test' acquired for 'shardCollection', ts : 5ec935b235505bcc59eb60c7
2020-05-23T10:39:46.637-0400 I SHARDING [conn25] distributed lock with ts: 5ec935b235505bcc59eb60c7' unlocked.
2020-05-23T10:39:46.640-0400 I SHARDING [conn25] distributed lock with ts: 5ec935b235505bcc59eb60c5' unlocked.
Of course the collection exists on primary shard:
rs0:PRIMARY> db.test.stats()
{
"ns" : "test.test",
"size" : 216,
"count" : 6,
"avgObjSize" : 36,
"storageSize" : 36864,
"capped" : false,
...
}
I have no idea what could be wrong here, i'd much appreciate any help :)
EDIT:
Here is the detail about steps i follom to run servers, i probably misunderstand something :
Config server:
sudo mongod --configsvr --replSet rs0 --port 27019 --dbpath /srv/mongodb/cfg
mongo --port 27019
Then in mongo shell
rs.initiate(
{
_id: "rs0",
configsvr: true,
members: [
{ _id : 0, host : "127.0.0.1:27019" }
]
}
)
Sharded server:
sudo mongod --shardsvr --replSet rs0 --dbpath /srv/mongodb/shrd1/ --port 27018
mongo --port 27018
Then in shell:
rs.initiate(
{
_id: "rs0",
members: [
{ _id : 0, host : "127.0.0.1:27018" }
]
}
)
db.test.createIndex({test:1})
Router:
sudo mongos --configdb rs0/127.0.0.1:27019
mongo
Then in shell:
sh.addShard('127.0.0.1:27018')
sh.enableSharding('test')
sh.shardCollection('test.test', {test:1})

Answer 1

That error happens sometimes when some routers have out of date ideas of what databases/collections exist in the sharded cluster.
Try running https://docs.mongodb.com/manual/reference/command/flushRouterConfig/ on each mongos (i.e. connect to each mongos sequentially by itself and run this command on it).

Answer 2

I just misunderstood one base concept: config servers and shard servers are distinct and independant mongodb instances, so each must be part of distinct replicasets .
So replacing
sudo mongod --configsvr --replSet rs0 --port 27019 --dbpath /srv/mongodb/cfg
with
sudo mongod --configsvr --replSet rs0Config --port 27019 --dbpath /srv/mongodb/cfg
makes the configuration work.