hpc documentation - technical:perceus:per-node-initd

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====== PERCEUS Per-Node init.d Augmentation ======

Normally, one would create additional VNFS capsules for any compute node that has additional services relative to the default VNFS image.  The alternate VNFS capsule would include the software associated with the services and any ''/etc/init.d'' scripts that are necessary to start the service at boot.  However, as time goes by any changes we introduce to ''/etc/profile.d'' or any YUM updates we must make would need to be replicated across all of the VNFS capsules.

The ''passwdfile'' and ''groupfile'' PERCEUS modules that are used to propagate accounting data to the compute nodes can add information on a per-node basis to forego the need for additional per-node VNFS images.  A similar approach has been adopted to allow for the startup at node boot of additional ''/etc/init.d''-like services.

===== The pernode-services Init Script =====

The absolute last ''/etc/init.d'' script that is run as the compute node boots is ''pernode-services''.  This script first searches for executable files in the ''/opt/perceus/state/lib/perceus/init.d/global'' directory; any executable files therein as run with a single argument:  ''start''.  This mimics the behavior of scripts in the ''/etc/init.d'' directory.
<note tip>Scripts can be named with sorting prefixes a'la the ''/etc/rc.#'' directories to provide ordered startup.</note>

Next, the script looks for a directory with a name matching the hostname of the compute node.  If ''n059'' is booting, then the script would look for ''/opt/perceus/state/lib/perceus/init.d/n059''.  If the directory exists, it is scanned for executable files and each is run with the ''start'' argument.  Again, ordered startup can be promoted using name prefixes, etc.

All executable files found will be executed; a non-zero return code from one will not prevent the execution of subsequent files.  However, a single non-zero return code will cause the ''pernode-services'' script to itself return non-zero on exit.

===== Common Functions =====

Just as ''/etc/init.d'' scripts have some common shell functions that are defined in ''/etc/init.d/functions'', the ''pernode-services'' scripts can source ''/opt/perceus/state/lib/perceus/init.d/functions'' to incorporate both ''/etc/init.d/functions'' and some functions provided by the ''pernode-services'' "package".

At this time, this includes adding ''/opt/perceus/state/lib/perceus/init.d/bin'' to the ''PATH'' to enable the ''waitOnFileUpdates'' command.

==== waitOnFileUpdates ====

This program takes a threshold (in seconds) and a list of one or more files/directories.  It checks the modification date on each against the threshold, marking any that are newer than the threshold time.  If all files/directories are marked, the program exits; otherwise, it sleeps for a certain amount of time before re-checking the remaining unmarked files/directories.

<note>The ''waitOnFileUpdates'' program was written primarily for the sake of watching the ''/etc/passwd'' and ''/etc/group'' files so that any per-node services that depend on accounting information derived from the ''passwdfile'' or ''groupfile'' PERCEUS modules can wait for ''provisiond'' to fetch the files from the PERCEUS master node.</note>

===== Adding Per-Node Services =====

The process is straight-forward.  For any services that should apply to all compute nodes, add an init script (executable bit set, of course) to ''/opt/perceus/state/lib/perceus/init.d/global''.  To add a service to a particular node, make sure a directory with the node's hostname exists in ''/opt/perceus/state/lib/perceus/init.d'' and add the init script to it.

For init scripts that will apply to multiple nodes (but not all of them), you will likely want to add the init script to one of the nodes and supply symlinks in the directories for the other nodes.  Or, akin to ''init.d'' itself, create a generic ''scripts'' directory in ''/opt/perceus/state/lib/perceus/init.d'' and add symlinks to the init script in ''scripts'' in each node's directory.

<note warning>Compute nodes will need to either be restarted after changes are made to the global/per-node ''init.d'' directory, or the applicable init scripts will need to be run manually via remote login as root.</note>