Cluster and Arbitrator questions

I know the answers to most of these questions, I just want to make sure I understand everything correctly and please answer me if you can.

  1. When creating a cluster and when we have 2 nodes, is an arbitrator only needed to avoid split-brain? For example, we have 2 nodes and one arbitrator, and after some time the Node A was disabled, the activation of the Node B must be done manually (since we have an arbitrator, split-brain will not occur)?. That is, what is the real functionality of the arbitrator? Did I understand correctly?

  2. When creating a cluster and when we have 2 nodes and don’t have arbitrator. At this time, when we select the first node as the primary node, is the cluster still running in active-active mode?

  3. When we have 3 nodes in a cluster, one primary node and the rest nodes secondary, is the cluster in active-active mode? At this point, there will be no split-brain as there are 3 nodes. If the primary node disconnects, will we have to manually select the second or third node as the primary? I think Yes.

  4. If I don’t have a load balancer and I have 3 nodes, if the primary node goes down, in this case, for example, the second node should be activated as the primary and the users should access the IP address of second node ( since we don’t have a load balancer)?

  5. When we creating a cluster and when we want to use arbitrator, in cluster creation process one node is activated as the primary, and then the arbitrator is added? or there is no need to select any node as primary? As I understand one node must be primary.

  6. When setting up cluster with arbitrator and one node is primary, it is necessary to use command: orbit elasticsearch setup, I have to use it on Primary and secondary (as stated in the official document)? senhasegura cluster settings
    **So, cluster setup steps ** :

  • Activate license on both nodes

  • Create cluster and mark one of them as Primary

  • Add arbitrator

Did I get it right?

  1. In what case does automatic switching from one node to another occur when, for example, we have 3 nodes in the cluster?

  2. How to make an active-active or active-passive cluster?

  3. Which linux version you usually use as arbitrator?

  4. For docker installation you use this guide and in addition install docker-compose and docker compose plugin?
    Install the Compose plugin | Docker Docs
    Install Docker Desktop on Ubuntu | Docker Docs

Hello Red,

  1. senhasegura uses a cluster technology where the nodes will have weight attached to them, when you have a pair number of nodes working, the primary will have weight 2, and the secondary weight

1.For the cluster to keep working, it is necessary to have at least 50,1% of the weight working. So, if the primary gets down, the cluster will stop working.
If the number of nodes is odd, like three nodes, every node will have a weight of 1, so if one of them is not working, senhasegura will keep working with the other two nodes. The arbitrator function is exactly to make the environment have three nodes instead of two, changing the weight of the nodes and allowing you to decrease the chances of having a split-brain scenario.

  1. The cluster configuration do not interfere in a node being active or passive, you chose this by changing the configuration presente in ‘Orbit Config. Manager → Settings → Application → Enable Application’.

  2. You can check more information on this and how it Works on the link: High Availability and Disaster Recovery

  3. Yes, if you do not have a load balancer, users will need to access nodes manually by choosing one of them and accessing their IP or DNS (if you have it configured).

  4. One node needs to be primary, and it will be the first node on the configuration order.

  5. The elasticsearch is an agent on senhasegura that has the information on the cluster members and their order. If you already have a cluster working and want to add an arbitrator, you will need to stop the elasticsearch and set it up again on every node starting from the primary.

  6. If you have three nodes in a cluster, the users can use all of them without any worries. If one of the nodes is down, you can just tell the users to use a different node, or if you have a load balancer configured, this organizing should happen automatically.

  7. For active-active, leave both instances activated on the previous path mentioned; for active-passive, leave only the primary active.

  8. You can use any Linux version as long as it is compatible with Docker and docker-compose.

  9. Since the Docker technology is something Linux related, we do not provide an installation guide for it.

PS.: Remember to Always take a snapshot before any configuration on cluster and/or arbitrator, and if you face any issues, you can always request support on our support portal so that we can help you with it.

Best regards.

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Thank you !!! :heart:

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