Helen: automatically start bundled services

[achirkin]

PROJECTS: helen
CHANGESET: create new component/module
DESCRIPTION:

An isolated task that does not require any knowledge of the project internals.

Currently, to set up the whole qua-kit environment, one has to run separately: qua-server, helen, and all helen services (at least siren and one more computational service). This is not so convenient, so I propose to let helen itself start the services she is aware of.

The changed helen pipeline as I imagine it:

• helen starts as usual and from time to time executes a special function (maybe in a separate thread)
• This function checks a special folder. For example, bundledServices subfolder w.r.t. helen executable.
• The folder contains some (arbitrary) files + a set of service-name.yml files. Each service-name.yml file contains command-line parameters to execute a corresponding service.
• Each time a service description yml file changes (or a new one is placed in the folder), helen should restart corresponding service using the information specified in the .yml file.

[NorfairKing]

I had another think about this, and everything in here is done except the automatic restarting.
If we really want this, we can use https://hackage.haskell.org/package/configurator-ng.
What do you think?

[achirkin]

I think, it is a little bit an overkill for now, but let's keep it open. Maybe we will add this in future, when we have more time for that

[NorfairKing]

I figured as much. Thanks!

[achirkin]

At this moment starting services seems to work. Though, there are couple things someone should resolve before closing this issue:

• A better logic for restarting services: if a service started successfully last time, but dropped due to some error while processing user messages, it should better not decrease restart counter.
• On some systems, occasionally, bundled services do not stop when helen stops, forcing a user to pkill the processes one-by-one.