Explore the ability to support dynamic configurations

[kevin-bates]

Use case: As an admin or dev ops engineer, I need the ability to change configuration parameters without restarting Enterprise Gateway.

Because Enterprise Gateway is a true multi-tenant environment, potentially hosting hundreds of users, it would be good to provide the ability to change configuration options without having to restart Enterprise Gateway.

Examples include adjusting the remote-hosts used by the DistributedProcessProxy, updating the unauthorized-users list, adjusting the culling timeout value, adding a kernel to the whitelist, etc.

From this comment:

Via a debugger I found that if I load the configuration after startup (and after making a change), I see the updated value reflected in the member (traitlet) variable. This implies that you could have a PeriodicCallback that simply refreshes the configuration (although this is another case where 'watching' is better). So things like remote-hosts, authorized-users, or whitelists could (in theory) be updated without having to restart EG.

[SolarisYan]

That's a practical feature

[kevin-bates]

I have an implementation ready. I think I'd like to wait a couple days to see how traitlets PR 521 unfolds. If it may take awhile for a release to occur, we can use temporary code that resides in EG.

[kevin-bates]

Update: We should be able to move forward with more "client-side" code once ipython/traitlets#522 is available in a release. This PR enables the ability to reload configuration files and, although not as fully baked in as we'd like (see ipython/traitlets#521), we can have that "driver code" in the application itself.