Feature proposal: Allow configuration from config file instead of CRD's

[grzesuav]

Proposal

Currently metacontroller is configured by recognizing CR's of type Composite/DecoratorController. This is about adding alternative way to provide config file, which content will be equivalent to those CR's, meaning it can be statically configured.

What will change

There will be:

• additional flag to point to config file
• config file describing metacontroller desired behavior

which will cause that:

• metacontroller will use the file as it would be CRD
• (probably) metacontoller will stop dynamically searching for additional configuration in cluster (but it depends on implementation and what will be easiet way to implement this)

Challenges

• provide some automatic way to read config file, probably yaml list and creation of objects in metacontroller to make this as smooth as possible for metacontroller to handle
• how it will impact auto-discovery, considering controller runtime

Options

• consider https://github.com/spf13/viper for config loading

[AmitKumarDas]

similar work has been done https://github.com/AmitKumarDas/metac/tree/master/config
All the references to above config should help to understand the challenges, usefulness, etc.

[adrianmace]

Based on the 12factor principles I'd recommend these configs be available as environment variables instead of / in addition to the file.

e.g.: COMPOSITE_CONTROLLERS=my-parent,my-child-1,my-child-2.

[grzesuav]

Based on the 12factor principles I'd recommend these configs be available as environment variables instead of / in addition to the file.

e.g.: COMPOSITE_CONTROLLERS=my-parent,my-child-1,my-child-2.

hmm I need to think if exposing complex config via env var is viable option