Database backed checks

[sislr]

hey @rameerez, nice gem! I especially like the DSL 🙌🏼

I saw that so far, the timestamps (e.g. last_run) are stored using a cache. This can be problematic for example when you run Sidekiq in a different process. Unless the app uses a shared cache between the processes, the last_run can't be updated within the worker.

the use case:

1. I have a Rails app and a separate worker (different process) for Sidekiq.
2. I then want to monitor the health of the process running in the worker

solutions I can come up with:
a) use a shared cache (solid_cache -> db-backed, redis_cache_store, ...)
b) patch the configuration layer to persist the timestamps with a db

a) is already possible. One can simply override the cache_store config.
b) requires a work around.

-> it would be nice if the persistence strategy is configurable. I imagine it as follows:
config.all_good.store = :db or config.all_good.store = :cache

with :cache it would use the existing cache_store class. with a :db setting, it could work as follows:

class HealthCheck < ApplicationRecord
  before_create :ensure_singularity

  validates :last_run, presence: true

  def self.instance
    first_or_create!(last_run: Time.current)
  end

  private

  def ensure_singularity
    raise StandardError, 'There can be only one instance' if HealthCheck.any?
  end
end

this would require an abstraction of the store