Can I setup 2 nodes cluster

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Vimol Chingkhu

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Nov 30, 2021, 4:16:36 AM11/30/21
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Hi,

I am looking to use rqlite in my application. It is possible that the application can be installed only on two nodes. Since my requirement is availability only.

Is it possible to setup rqlite 2 nodes cluster?

Regards,
-Vimol

Philip O'Toole

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Nov 30, 2021, 7:42:53 AM11/30/21
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Yes, you can run a two-node cluster, but it does not provide any more availability than a 1 node cluster since a 2-node cluster requires both nodes to be up.


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Vimol Chingkhu

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Nov 30, 2021, 8:24:30 AM11/30/21
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Thanks Philip. 

One more question. In the FAQ, it mentions that max of 9 writes nodes is practical. 
But can I still add more than 9 write nodes? My application may scale up to 64 nodes.
What would be the impact if it is more than 9 write nodes?

Regards,
-Vimol

Philip O'Toole

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Nov 30, 2021, 8:48:50 AM11/30/21
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You can add as many nodes as you like, there is no theoretical limit.

More nodes means more nodes must agree (N/2+1 where N is the total number of nodes), that's all. But larger and larger numbers of nodes may become hard to manage, and put more load on the leader. But you can certainly try it out.

Vimol Chingkhu

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Jan 4, 2022, 11:45:59 PMJan 4
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Hi Philip,

You mention that for 2 node cluster requires both nodes to be up.

Is there any setting to make the cluster run if one node is down?

Regards,
-Vimol

On Tuesday, November 30, 2021 at 6:12:53 PM UTC+5:30 Philip O'Toole wrote:

Philip O'Toole

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Jan 5, 2022, 9:34:57 AMJan 5
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On Tue, Jan 4, 2022 at 11:46 PM Vimol Chingkhu <kvi...@gmail.com> wrote:
Hi Philip,

You mention that for 2 node cluster requires both nodes to be up.

Is there any setting to make the cluster run if one node is down?

No, as that would be completely at odds with what Raft is about. rqlite is not a primary-replica type of system.

If the second node goes down, you would need to *remove* that node from the cluster, thereby reducing the cluster to a system one-node in size. But you would need to restart the remaining node to perform this removal, as quorum would have been lost.


When the second node came back up, you would need to explicitly join it back to the leader. 
 

Regards,
-Vimol

On Tuesday, November 30, 2021 at 6:12:53 PM UTC+5:30 Philip O'Toole wrote:
Yes, you can run a two-node cluster, but it does not provide any more availability than a 1 node cluster since a 2-node cluster requires both nodes to be up.


On Tue, Nov 30, 2021 at 4:16 AM Vimol Chingkhu <kvi...@gmail.com> wrote:
Hi,

I am looking to use rqlite in my application. It is possible that the application can be installed only on two nodes. Since my requirement is availability only.

Is it possible to setup rqlite 2 nodes cluster?

Regards,
-Vimol

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