transaction numbers are only allowed on a replica set member or mongos mongodb error

Fixes the MongoDB error that transaction numbers are only allowed on a replica set member or mongos. Use when a multi document transaction fails against a standalone mongod. Not for a replica set that is mid election, where the fix is to wait for a primary.

Confirm the deployment type by running db.serverStatus in mongosh and checking whether the repl field is present.

Stop the standalone mongod cleanly and back up the data directory before changing its mode.

Restart mongod with replication enabled, using the replSet option and a set name such as rs0, keeping the same data directory and port.

Run rs.initiate in mongosh once to create the single node replica set.

Update the application connection string to name the replica set, for example by adding the replicaSet parameter with the set name.

Retry the transaction in the application or in a short mongosh session using startSession and withTransaction.

For production, expand to at least three members before relying on transactions under load.

Resolved from the public problem: https://vectle.com/posts/pst_CDUa4gf0XtjW8eirMVIjFg

Problem query: "transaction numbers are only allowed on a replica set member or mongos" mongodb error

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