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Taikun OCP Guide

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Configure SSH between compute nodes

Consider merging this into a larger “migration” document or to the
installation guide

If you are resizing or migrating an instance between hypervisors, you
might encounter an SSH (Permission denied) error. Ensure that each node
is configured with SSH key authentication so that the Compute service
can use SSH to move disks to other nodes.


It is not necessary that all the compute nodes share the same key
pair. However for the ease of the configuration, this document only
utilizes a single key pair for communication between compute nodes.

To share a key pair between compute nodes, complete the following

  1. On the first node, obtain a key pair (public key and private
    key). Use the root key that is in the /root/.ssh/id_rsa and
    /root/.ssh/id_rsa.pub directories or generate a new key

  2. Run setenforce 0 to put SELinux into permissive

  3. Enable login abilities for the nova user:

    # usermod -s /bin/bash nova

    Ensure you can switch to the nova account:

    # su - nova
  4. As root, create the folder that is needed by SSH and place the
    private key that you obtained in step 1 into this folder, and add the
    pub key to the authorized_keys file:

    mkdir -p /var/lib/nova/.ssh
    cp <private key>  /var/lib/nova/.ssh/id_rsa
    echo 'StrictHostKeyChecking no' >> /var/lib/nova/.ssh/config
    chmod 600 /var/lib/nova/.ssh/id_rsa /var/lib/nova/.ssh/authorized_keys
    echo <pub key> >> /var/lib/nova/.ssh/authorized_keys
  5. Copy the whole folder created in step 4 to the rest of the

    # scp -r /var/lib/nova/.ssh remote-host:/var/lib/nova/
  6. Ensure that the nova user can now log in to each node without
    using a password:

    # su - nova
    $ ssh *computeNodeAddress*
    $ exit
  7. As root on each node, restart both libvirt and the Compute

    # systemctl restart libvirtd.service
    # systemctl restart openstack-nova-compute.service


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