Persistent cache of properties on config client

I don't know whether others would find such a feature useful as one should really make sure config server is highly available. However, when I suggested that we use this awesome open source tech for centralizing our properties, I was asked to provide a failsafe feature on the client-side. Basically, if enable and path set, the client will create and update a failsafe properties file that contains all properties acquired from the config server last. If cannot connect, it will use the failsafe config.

Of course, this would open a discussion about should failsafe happen what kind of notification should take place. In our case, the requirement is simply to log a warning that this took place. A technique like this may already be doable with client as is and I just don't see it?

The issue names no files, tests, or entry points, so first inspect the config client’s existing property acquisition and connection-failure handling. Define the persistent failsafe file’s enablement, path, update, fallback, and warning behavior, then add coverage for successful updates and unavailable config-server fallback.