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The inventory may define these hosts:
observers: Set of hosts to observe the cluster (only the first is considering)Hypervisors: Set of machines to hosts VMs.
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Remember that the cluster must contain an odd number of machines. For example, three hypervisors or one observer and two hypervisors. |
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All nodes in the cluster have access to a shared storage via Ceph (see Shared storage section). With it, the cluster is in N to N redundancy mode.
Corosync will provides messaging and membership services.
Pacemaker will manage the cluster (synchronize resources between each node).
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More details on Pacemaker here and Corosync here.
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For instance, with pacemaker-remote pacemaker can monitor services and containers directly inside a VM.
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For more information about pacemaker-remote refer to https://clusterlabs.org/pacemaker/doc/2.1/Pacemaker_Remote/singlehtml/.
Management tool
The vm_manager project is an a high-level interface of pacemaker and Ceph to manage the VM like a resource. He is installed during the installation step and provides the vm-mgr command.
Please refer to How to manage VM in SEAPATH for more detais.
Node replacement
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replacement
In case one of the nodes suffers a difficult to repair situation (lost motherboard for example, or lost disk with no RAID), it might become necessary to replace the server with a blank one.
From the cluster point of view, we will need to remove the old node and add the new one, for both corosync/pacemaker and ceph.
The
ansible/playbooks/replace_machine_remove_machine_from_cluster.yamlplaybook can remove a node from the cluster. For this, themachine_to_removeshould be set to the hostname to remove.
The below command should be
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launched in the ansible project.
Code Block language bash cqfd run ansible-playbook -i /path/to/inventory.yaml -e machine_to_remove=HOSTNAME playbooks/replace_machine_remove_machine_from_cluster.yamlA new
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host should be
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installed with the ISO installer and the same hostname, ip address, etc... than the old node.
Make the "cluster network" connections between hosts.
Restart the cluster_setup_debian.yml playbook to configure the new host in the cluster (more details here).
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