Different ways of configuring webapps

Question

I'm writing scripts to deploy apps under Tomcat. There are different ways of configuring these apps:

• Keeping properties files in a source directories like WEB-INF which would mean we need to extract sources and replace those files with what we need for particular env
• Configuration based on env properties, this looks like a bad option as for me, files are more explicit and less magic, and less work on separating apps on the same machine
• There are also options to configure TOMCAT_HOME/conf/[app_name].xml and treat those properties as env vars in our apps. But in this way it won't be possible to move to Jetty for instance if we would want to do that because these files are Tomcat-specific.

Could someone provide other options and share their opinions on the listed above? Consider these criteria: easiness of configuring, portability, standards, explicitness (don't like magic, other people may not understand it), OS (main OS is Linux, but others may want to run it on Windows).

Answer 1

I'd recommend putting properties into a database table (which of course implies, your application has a datasource).

We prefer this method in our web applications for the following reasons:

• Properties are separated from the deployed artifact and application's install directory
• Peoperties can easily be accessed by database tools
• Properties can have additional attributes, like a type or a default value
• Properties can easily be changed during runtime (provided the web application has some admin page to reload them)
• Depending on the environment (e.g. development, test, production) you can have different sets of properties and load them in the same way as other master data

In cases where you don't have a database at all, another solution is just to use system properties and read them by System.getProperty(key), which is ok for a system under your control and not too many properties.

Answer 2

You can use configuration based on env properties by using files. What I mean is that you can write a Context.xml file under the META-INF of your web application setting up the environment or configuration following this rules.

I find that using env properties provides easy configuration, is based on context and dependency injection. You can use the new java API's eg. the @Resource annotation. It will work under any application server, etc.

Answer 3

In my experience it worked well using and environment variable for the conf dir: {APP_NAME}_CONF_DIR. If this is not set the application will default loading from /etc/{app_name}/conf . Most of the time you will not have to set the env. variable as you will use the default dir.