Chapter2: Lab: Deploy a Replica Set

Hi community!
After working on this lab for 1 hour, I have passed 11/12, see details:

It says I haven’t add localhost:27002 to the ‘m103-repl’ replica set. I have no doubtly not add replica yet, snice I returns error message when I use rs.add(“m103-repl:27002”), error message see below:

I am not sure that if I direct a wrong replica file path, but when I reconnect to primary node I use this path:

So the problem is I may use a wrong path to direct node, or secondary nodes should use different path.

But I have no clue for now.

Could someone give me some hint?


Hey @Tianyi_Hu,

The above way as you shared is not the correct way to add the replica set for the node localhost:27002. Try this way:

Screenshot 2022-01-10 at 7.02.28 PM


I hope this helps!

In case you have any doubts, please feel free to reach out to us.

Kushagra Kesav


Thanks! That work well!
But I am kind of confused. After I initiated the rs, I reenter into mongo with --host “m103-repl/localhost:27001” That means I direct the mongo into a path of primary node, right?
Then I am add two nodes (localhost: 27002 and localhost:27003), with rs.add(“localhost:27002”) and rs.add(“localhost:27003”), why I don’t need to type m103-repl since node 2 and node 3 are use same replSetName with node1?
I think that is why I add replica set in incorrect way.


Hello @Tianyi_Hu,

The syntax of rs.add() to add new node to the replica set is


So, here localhost is considered to be the host in the case of the our IDE as also mentioned in the configuration file. And 27002 is the port number.

I hope it helps!

Let us know if you have any other questions or concerns.


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Get it! Thanks!
Say if in the config, I write the path of node 2 for “m103-repl/localhost:27002”, then when I try to add node 2, it still gonna be rs.add(localhost:27002). For the host is localhost but not m103-repl/localhost, correct?


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Correct :white_check_mark:

Here m103-repl/localhost:27002

m103-repl → replica set
localhost → host
27002 → port number


1 Like

Get it!

Thanks a lot!!


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