MongoError: not master and slaveOk=false

[freezy]

View details in Rollbar: https://rollbar.com/freezy/server/items/59/

MongoError: not master and slaveOk=false
  File "/var/www/server/production/v2.3.8/node_modules/mongoose/node_modules/mongodb/lib/core/connection/pool.js", line 454, in Connection.<anonymous>
              return handleOperationCallback(self, workItem.cb, new MongoError(responseDoc));
  File "events.js", line 126, in emitTwo
  File "events.js", line 214, in Connection.emit
  File "/var/www/server/production/v2.3.8/node_modules/mongoose/node_modules/mongodb/lib/core/connection/connection.js", line 368, in processMessage
        conn.emit(
  File "/var/www/server/production/v2.3.8/node_modules/mongoose/node_modules/mongodb/lib/core/connection/connection.js", line 537, in Socket.<anonymous>
                  processMessage(conn, emitBuffer);
  File "events.js", line 116, in emitOne
  File "events.js", line 211, in Socket.emit
  File "_stream_readable.js", line 263, in addChunk
  File "_stream_readable.js", line 250, in readableAddChunk
  File "_stream_readable.js", line 208, in Socket.Readable.push
  File "net.js", line 601, in TCP.onread