Reading data from a Mongo slave

Quick tip - if you are running Mongo DB and have configured slave servers, you can’t access the data from the slaves by default.

  ~$ mongo
  testRs0:SECONDARY> use test_db;
  testRs0:SECONDARY> db.test.getIndexes()
  Mon Aug  5 21:09:36 uncaught exception: error: { "$err" : "not master and slaveOk=false", "code" : 13435 }

Gah :P

Fortunately you can tell Mongo to allow operations on the slave:

  tests0:SECONDARY> db.getMongo().setSlaveOk();

After that, you can use the Mongo slave the same way you would the master. Note however, that you’ll need to run this command every time you log into a Mongo terminal session to read data.