Define explicit health check resources for HTTP services

[kyujin-cho]

Main idea

• Create unified health check resource for every components
• Disable logging access footage of health check resource
• Extend health check API handler implementation to report connection status of each dependent components (redis, etcd, ...)

Though we already have HTTP resources dedicated for reporting its current health on some components (e.g. GET / for manager), for ease of management, let's create a unified health check method across every Backend.AI services with HTTP server. Key requirements are:

• Health check request should be called by GET /health
• Response should be formed as:
  • name of the component and its version in JSON format when Accept request header contains application/json
  • 204 No Content otherwise
• Access log to the health check resource should not be posted since otherwise it will spam the whole log

Alternative ideas

No response

Anything else?

No response