[SERVER-24385] mongos can't write to config server replica set (CSRS) (invalid write concern) Created: 03/Jun/16  Updated: 14/Jul/16  Resolved: 03/Jun/16

Status: Closed
Project: Core Server
Component/s: Sharding
Affects Version/s: None
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Geoff Pitfield Assignee: Unassigned
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Operating System: ALL
Steps To Reproduce:

Set up mongod 3.2.6 replica set per https://docs.mongodb.com/manual/tutorial/deploy-shard-cluster/. Start mongos 2.6.12 pointed at that replica set.

Participants:

 Description   

When I start the mongos instance, I get a string of errors along the lines of `getLastError command failed: w: 'majority' is the only valid write concern
when writing to config server replica sets, got:

{ w: 1, wtimeout: 0 }

`. This prevents mongos from being able to access and modify the config server, and thus the entire sharded cluster doesn't work.

I really hope I've just done something stupid instead.



 Comments   
Comment by Geoff Pitfield [ 03/Jun/16 ]

Hi Stephen,

Thank you so much for the quick answer. Unsurprisingly, I did do something stupid - mongod was installed via a 3.2 docker image, whereas I pulled mongos via yum and it was the earlier version. I didn't realize that the versions synced up across the different components. FWIW, I did also post on Stack Overflow, but in a fit of panic had concluded that this must be a bug, which retrospectively was silly but there you have it.

Thanks again for the rapid response.

Cheers,

-geoff

Comment by Stennie Steneker (Inactive) [ 03/Jun/16 ]

Hi Geoff,

You cannot use a version of mongos prior to 3.2 with the new Config Server Replica Sets configuration which was added in MongoDB 3.2. In general, mixing major server versions in a deployment is also not supported aside from transiently when upgrading between successive major releases (i.e. 3.0 => 3.2). If you are deploying a new cluster using MongoDB 3.2.6, all components should be using 3.2.6.

Please note that the SERVER project is for reporting bugs or feature suggestions for the MongoDB server. For MongoDB-related support discussion please post on the mongodb-user group or Stack Overflow with the mongodb tag, where your question will reach a larger audience.

See our Technical Support page for additional support resources.

Regards,
Stephen

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