Add pluggable component for health check feature

[jeevatkm]

The goal is to create a pluggable component for health check feature in aah.

Goals:

• Fundamentally application must have flexible health check implementation
• Also for cloud native - Kubernetes Liveness and Readiness probes

Design:

• Create a go library
  • Repo: https://github.com/go-aah/ec-healthcheck-provider - created, ready to use
  • Go Vanity for release: aahframe.work/ec/healthcheck - yet to be done
• Spec:
  • Provide an interface for implementing health check reporter
    • interface method func Check() error
  • Provide a method to create new health check component
  • Provide methods to add one or more health check reporter into health check registry with or without interval duration to call
    • e.g.: hc.AddReporter(healthcheck.Config{/* report name, implementation based on above interface, duration, skip on error, etc... */})
  • Provide a method to register controller and route for the aah application (by domain name if multiple domains application)
    • For non-Kubernetes - accept URL relative path for the route - returns the response payload with status code
    • For Kubernetes - to add liveness and readiness endpoints (accept URL relative path for the route for both endpoints) - return only status code with empty body since Kubernetes only cares about status code

• Status Codes for response
  • 200 OK if every registered health checker/reporter returns nil
  • 503 Service Unavailable if any registered checker/reporter return non-nil except skip on error

Sample response payload (a conceptual idea, yet to be finalized)

{
	"status": "OK", // OK or Service Unavailable
	"timestamp": "RFC3339 or ISO 8061", // yet to be decided
	"reportname": bool, // true or false, this line will be repeated for all registered health checker/reporter
}

[jeevatkm]

@adrianlop welcome 😄

[adrianlop]

I just pushed a basic PR here: https://github.com/go-aah/ec-healthcheck-provider/pull/1/files

let's discuss and review in there if you like! cheers @jeevatkm

[jeevatkm]

@adrianlop I have added Go vanity for aahframe.work/ec/health so available to use for try/test https://godoc.org/aahframe.work/ec/health

Until official release, please do go get aahframe.work/ec/health@master in your application to test/use it will update your go.mod with latest version of library every time you run it.