CentOS 7.x Rocks cluster 7.0 Build compute server

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By default compute nodes are named compute-0-0.local, compute-0-1.local (assuming .local is used as domain name for private network). The compute nodes are setup via Pxeboot. They should be connected only to private network and then booted via network. Ideally compute nodes should be configured to boot via network as primary option and then via hard-disk as secondary.

To setup compute node use:

1. Before doing network boot on compute node, on master server, run below command:

   insert-ethers

2. On the ncurses based popup Choose Compute, it would display: 'insert-ethers is waiting for new compute nodes.'
3. After this boot the compute node via network.
4. When the frontend machine receives the DHCP request from the compute node, It will display, "Discovered a new appliance with MAC"
5. insert-ethers has discovered a compute node. The "( )" next to compute-0-0 indicates the node has not yet requested a kickstart file. You will see this type of output for each compute node that is successfully identified by insert-ethers.

   00:13:72:ba:c8:df       Compute-0-0         ()

6. Kickstart files are retrieved via HTTPS. If there was an error during the transmission, the error code will be visible instead of (*).

   00:13:72:ba:c8:df       Compute-0-0         (*)

7. The compute node has successfully requested a kickstart file from the frontend. If there are no more compute nodes, you may now quit insert-ethers by pressing F8.
8. Compute node will intall automatically.
9. After successful installation of compute node, it will restart.
10. We can list of hosts which are part of rocks cluster using

    rocks list host

Ref:

• http://central-7-0-x86-64.rocksclusters.org/roll-documentation/base/7.0/install-compute-nodes.html

Custome hostname

If we want to give some other hostname then we can use:

insert-ethers --hostname <desired-name>

For example

insert-ethers --hostname gpu

When we use option such as --hostname, we can setup only one node at a time. Once the node successfully requests pxeboot file, insert-ethers exits automatically.

For information on other options taken by insert-ethers refer http://central-7-0-x86-64.rocksclusters.org/roll-documentation/base/7.0/insert-ethers.html

ssh to compute node

To ssh compute node simply use:

ssh <node-name>

For example

ssh compute-0-0
ssh gpu

There is automatic authorized key setup from master to all compute. So no password is required. No prompt would be there to accept ssh fingerprint / key either. It would directly get connected.

Solving httpd not started issue while using insert-ethers

It is possible for httpd to fail to start with errors such as below in /var/log/httpd/error_log file:

[Thu Jul 07 06:35:56.564016 2022] [auth_digest:error] [pid 8490] (2)No such file or directory: AH01762: Failed to create shared memory segment on file /run/httpd/authdigest_shm.8490
[Thu Jul 07 06:35:56.564030 2022] [auth_digest:error] [pid 8490] (2)No such file or directory: AH01760: failed to initialize shm - all nonce-count checking and one-time noncesdisabled

To solve this use:

mkdfir /run/httpd
chown apache:apache /run/httpd
systemctl start httpd

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