[Hawkular-dev] About configuration

[Lukas Krejci]

I am not for or against using properties for config simply because I do not 
yet know what the requirements for the configuration will end up being.

On the other hand I feel we should from the start use something that is 
capable of handling more structured configuration formats without us needing 
to rewrite all the configuration handling code if that need arose (by 
abandoning java's Properties and moving to something different).

Hence I propose using Apache Commons Configuration for reading the 
configuration files. I think Artificer uses it, too, so Brett et al. can 
comment if that would be the right thing to do or not.

Commons configuration supports XPATH for accessing nested data so working with 
hierarchical properties should be quite nice with it. The disadvantage is that 
it drags several other deps with it - 
http://commons.apache.org/proper/commons-configuration/dependencies_1_10.html.

Other option could be to commit to a single configuration format and use a 
dedicated parser for that with minimal deps. For example if we chose JSON as 
the config format we could use JBoss DMR for reading/writing such configs. The 
advantage of that approach is that DMR is absolutely tiny with no external 
deps. The disadvantage is that JSON cannot have comments (which is easily 
amended by a custom reader that would strip the comments before the contents 
are passed to DMR for parsing (a recommended approach from the author of JSON 
- https://plus.google.com/118095276221607585885/posts/RK8qyGVaGSr)).

On Thursday, February 05, 2015 11:01:53 Thomas Segismont wrote:
> Hi everyone,
> 
> Yesterday Lukas asked on IRC if there was a discussion about
> configuration. AFAIK, there wasn't, hence I'm sharing how we support
> configuration in metrics.
> 
> # Metrics REST server
> 
> The REST server runs on top of Wildfly.
> 
> Configuration is a set of key/value pairs (configuration properties)
> defined by the following sources, in order of precedence:
> 
> * system properties (-Dkey=value)
> * external java.util.Properties file, which path is defined by the
> metrics.conf system property; by default, <user.home>/.metrics.conf is
> used (if it exists)
> * internal java.util.Properties file (META-INF/metrics.conf)
> 
> The rationale behind is that the system should be able to:
> 
> 1. start with reasonable defaults
> 2. switch to another configuration easily
> 
> # pTrans
> 
> pTrans is different because it's a standalone application, so it's much
> easier to follow the daemon configuration habits.
> 
> pTrans takes a path to a properties configuration file as a program
> argument. This argument is mandatory.
> 
> # Configuration file format.
> 
> metrics started with properties file and I think it's fine.
> 
> But if we feel the need for a more structured format, we should pick
> something which can be easily parsed by a variety of programming
> languages, especially languages widely used for administration (Python
> and Ruby).
> 
> 
> Regards,
> Thomas
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