Paul Krizak wrote:
I've got a question about what you guys think the best solution is in
this situation.
I've got some files that must be customized on a per-host basis, but are
based on a common "root" file. My goal is to have the following system:
* When the system is first installed, or if the file on the system is
wildly different than the master, a copy: statement pulls down a fresh
copy of the file, which an edifiles: stanza corrects for that specific
host.
* Later, if the master file changes, the clients should "know" to pull
down a new copy of the file, and then perform the same editfiles: stanza
again.
Using "checksum" for the copy statement doesn't really work, since once
you make a change to the file using editfiles:, the checksums don't
match and thus the file gets copied every time. On the upside, you're
guaranteed to always have the correct version of the file on the target
system.
Using "ctime" for the copy statement *sounds* good, as the copy only
happens when the "master" file updates on the server. Where this falls
flat, however, is on freshly installed systems, where the ctime of the
*incorrect*, freshly-installed file is *later* than the ctime of the
"master" file. In this situation, the "master" file is not copied (and
I wouldn't expect it to).
I've got several cases in my (very lengthy) cfengine config where I run
into this type of issue. For small files, I can put the entire contents
of the file into an editfiles: block and avoid using copy: at all. This
doesn't work for large files, however, as I don't want a cf.* file to
have a 5,000-line config file in it with Append statements.
For large files, I use checksum copies and just accept the fact that
they will get copied every time cfagent runs.
I'm looking to improve convergence in my config files...anybody else
have clever workarounds for this problem?
cfengine is a great general purpose tool, but is very clunky for certain
purposes. The example you give is one which is possible to implement as
a pure cfengine solution, but which can be made easier by bringing in
more specific 'helper' apps.
To create a 'target' file based on a 'source' file, along with some
parameters and processing rule is territory well covered by 'make'.
Simply copy the template and the Makefile using checksum, and invoke a
make in shellcommands. A single Makefile can have the rules for creating
any number of config files and can run make in any number of other
direcories. Running 'make' on up-to-date files is generally quick, but
triggering make using a class may be more efficient. Perhaps something
like 'main.(make_needed|Hr02)::'. When I use make in cron jobs I usually
pipe the output into grep -v to filter out 'makefile is up to date'
messages, so I only get mail when the makefile triggers.
To perform the transformation from template to production file you can
use awk, sed, m4. m4 is a particulary good choice as it allows most of
the decision making to be imbedded in the template, steered by variables
that can be defined on the command line. m4 allows simple substituion,
conditional text (ifdef and ifelse), file inclusion (include) and
complex macro expansion.
Regards
Frank Ranner
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