Running non-sharding setup with only 1 replica

MongoDB Percona Operator for MongoDB
1

Hello

May be I missed that but is it possible to run the “non-sharding” setup with only one replica ?

[edit] … and what is the absolute minimum, so that a cluster is responsive, even if a replica would be down (for ex due to GKE nightly maintenance) ?

Regards
John

2

hey John,

May be I missed that but is it possible to run the “non-sharding” setup with only one replica ?

Did you mean single-member replicaSet? Then yes. For the normal setup, to convert a standalone, you will need to add the below configuration to mongod.conf file and restart:

replication:
  replSetName: "rs0"

Then initiate the replicaset as follows:

rs.initiate()

.
For the psmdb operator, keep spec.sharding.enabled: false and spec.replsets.size: 1 in cr.yaml. See here and here.
From my test:

$ kubectl get pods -n psmdb 
NAME                                               READY   STATUS    RESTARTS      AGE
my-cluster-name-rs0-0                              2/2     Running   5 (24h ago)   33h
percona-server-mongodb-operator-85779f9cd7-6xklq   1/1     Running   6 (24h ago)   6d23h

From the values of cr.yaml:

$ kubectl get psmdb -n psmdb -o=jsonpath='{.items[0].spec.replsets[].size}' 
1
$ kubectl get psmdb -n psmdb -o=jsonpath='{.items[0].spec.sharding.enabled}' 
false

.

[edit] … and what is the absolute minimum, so that a cluster is responsive, even if a replica would be down (for ex due to GKE nightly maintenance) ?

Can you explain this clearly? In the above statement, you mentioned non-sharding and here you are asking about the sharded cluster stability when a replica is down. If you are asking about fault tolerance of a replicaset, then refer here. Else if you could explain the architecture and your end goal clearly, then we may try to help you with that direction.

Regards,
Vinodh Guruji

3

To add more to what @Vinodh_Krishnaswamy said, you might also need to disable unsafe flag (if you use old version, otherwise operator will scale it up to 3 automatically).

Read more about unsafe flag here: Custom Resource options - Percona Operator for MongoDB

Also feel free to book me here: Zoom Scheduler
if you want to chat about it and open to share your use cases :slight_smile: