Mongo replication test

The most important links

Building and breaking replica sets in MongoDB

How do I do things?

First and foremost, read the most important link above!! This step is VERY IMPORTANT.

• Pull the repo down
• Run npm run init to create mongo folders
• Run npm run start-mongo1 in terminal window 1 to start the primary server
• Run npm run import-data another terminal window (terminal window 2) to put some data in there

Setting up replication

In terminal window 2, run mongo and run the command db.restaurants.find({}, { _id: 1 }).limit(20).forEach(printjson). This should print out a set of 20 object IDs.

A replica set can be set up using rs.initiate(). Once this is done, run rs.status() to check the status of the replica set. You should see <your_replica_set_name>:SECONDARY> at the prompt. Once a query is run, like the one above, you should see the prompt change to <your_replica_set_name>:PRIMARY>.

In another terminal window (terminal window 3), run npm run start-mongo2 to start the secondary server. Back in terminal window 2, run mongo if you quit mongo earlier and then run rs.add('computer_name:27018'). Replace computer_name with your computer name. You should get a message saying { ok: 1 }. This means that the primary knows about the secondary mongo server BUT they are still not synced.

In terminal window 4, run mongo and try to run a query like the one above. It should fail with an error. After the error, run rs.slaveOk() to sync the two mongo databases. Once the sync happens, running a query should yield the same results on both servers.