feat(HEALTHCHECK): add healthcheck instruction in Dockerfile to check mongo status

[jerome-lecorvaisier]

Hey,

Even if everyone knows that mongo is so strong to be unhealth, this feature could be useful.
Maybe there is a best way to check mongo status and/or interval and timeout values could be adjusted but anyway, that's a first try.

• Could be related to MongoDB Health Check #105

Have fun

[tianon]

I think @yosifkit's comment over in docker-library/cassandra#76 (comment) still accurately summarizes my own feeling about adding an explicit HEALTHCHECK instruction to official images:

I do not feel that generalized healthchecks on the official images are really that useful.

• users will have their own idea of what is "healthy"
• it does not actually test that the service is listening to connections outside of localhost (see https://github.com/docker-library/healthcheck for some examples that do more than what's proposed here, including attempting to check whether the service is listening remotely)
  • some of the Official Images even purposely start in a localhost only mode for database initialization and then kill and start the main service with full network availability
• after upgrading their images, current users will have extra unexpected load on their systems for healthchecks they don't necessarily need/want and may be unaware of

[yosifkit]

closing based on previous comment.