General description of installation of hosts with cfengine

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The installation of New World hosts follows a number of principles:

  1. All hosts run Debian
  2. cfengine is used to take a host from a minimally-installed Debian condition to CSE-usefulness[1]
  3. To get a host to the "minimally-installed Debian" condition we accomodate:
    • AWS Debian-provided machine instances, or
    • Virtual machines or physical hosts booted from a standard Debian install DVD:
      • With the root disk partition so everything is in the one partition except for swap, and
      • With networking configured via DHCP, or
      • With networking configured statically, and
      • With a minimal configuration selected manually[2], or
      • With a minimal configuration loaded via the network (see preseed and Installing a lab computer), this being the common/batch/standard way to install many identically-configured hosts, such as lab computers, as it allows cfengine to be installed and started automatically
  4. The basic sequence of operations of any cfengine (read: cf-agent) run is as follows. This includes an initial install:
    1. Download an updated promises.cf file, if available
    2. Download an update host-specific "personalisation" configuration file defs.json, if available
    3. Create, instantiate or update configuration files
    4. Install or remove system-specific Debian packages
    5. Install or remove teaching-specific Debian packages
    6. Update teaching-specific extra files
    7. The promises.cf also controls the restarting or reloading of systemd services if/when configurations are changed

Limiting expectations of cfengine

There is no expectation or desire that cfengine will always take servers the "last mile". Installing a few final packages and making a few configuration changes is generally expected to be done manually when a host is installed to give the host or server its final "personality" or features. This is so:

  1. cfengine's configuration doesn't contain too much magic so as to make it inscrutable, and
  2. To ensure CSG staff retain administration skills.

Footnotes

  1. ↑ Amongst other things, this "usefulness" refers to being able to access CSE's UDB, access home directories, have CSE-specific programs and tools installed, have a full list of CSE hosts and IP addresses in /etc/hosts, and have a full set of Debian packages used for teaching installed.
  2. ↑ When selected manually the minimal configuration should include only SSH server.
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