Compute Node Deployment (Admin Guide)

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Admin Guide Compute Node Deployment
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Deployment Software

There are lots of software tools to install a node. This article just tries to give a small overview:

Warewulf

If you use OpenHPC the first deploy is usually done using warewulf. How to use it is explained in great detail in the Installation Recipes. Warewulf works fine for what it promises, but there are a few drawbacks (last I checked):

  • Warewulf brings its own version of ipmitool which does not support lanplus protocol (only lan) which is needed for many Dell servers. This can be remedied by deleting the /usr/libexec/warewulf/ipmitool binary and setting a symlink to the OS /usr/bin/ipmitool.
  • The installation environment is pretty limited, for example it is not possible to create LVM volumes during installation so one is limited to 7 partitions (which is sometimes not enough).
  • warewulf uses an apache webserver to copy the /etc/{passwd,shadow} files to the compute nodes without any kind of authentication of the client (only the MAC address is used to identify the client). This is a huge security concern.

xCAT

Another option is xCAT (Extreme Cloud Administration Toolkit, https://xcat-docs.readthedocs.io/en/stable/index.html). There are many talks and websites about it and while it is very powerful it is also a complex piece of software. Especially tuning it correctly to deploy many nodes quickly is said to be quite difficult.

luna

In the Unix tradition, luna is a software that pretty much only does one thing, but does it very well: Install nodes. It’s a project of a former ClusterVision employee and hosted on github, licensed under GPLv3. The software itself just binds together a database and some other open source software (mainly dracut) using a few python and C programs. One can easily look throug the while code in an afternoon. The installation is very quick with low load on the servers because all clients during installation run a small bittorrent client which is used to distribute the image data among all nodes.


Notes about Deployment

Some thoughts about deployment:

  • In this age, images to be deployed should be created on disk (for example using yum --installroot) rather than installing a “golden” node using kickstart from which is later than read a complete hard disk image.

  • System Users (UID) and Group IDs (GID), i.e. anything below 500, should not be left to chance. Many UIDs and GIDs are fixed but there are still many dynamic ones. Before starting to install packages into an image directory, /etc/passwd and other files with all expected user and group entries should be created there. The files /etc/passwd, /etc/group, /etc/shadow, /etc/gshadow haveto be created with suitable content.

  • We prefer not to have to run a configuration software like Ansible or others over all our compute nodes but prefer to have the nodes “self-configurable”. Our nodes use a naming scheme that contains location data like Rack, Chassis, and Node Numbers. This data is taken from the hostname and used on startup by cron scripts to self-configure the node, i.e. write some configuration files.