Allow usage with Rails 3

[mecampbellsoup]

Current Behavior

Does not work with Rails 3 due to gemspec versioning of the rails dependency.

Why Change?

We'd like to use this gem within zipmark-service which is a Rails 3 application.

Implementation

• lower rails version dependency from 4.2 to 3.2 in the gemspec
• only evaluate ActiveRecord::Migration::CheckPending.class_eval block if Rails version is >= 4

[mecampbellsoup]

@jakehow @kurko please review (moved from #1)

[kurko]

Looks good-ish. This lib has no tests though.

Could you give me a bit more context into this? It's called allow_connection_failure, does it mean that if we get a genuine database connection error, we will ignore them (as if the app had no DB in the first place)?

What apps are using this lib?

[jakehow]

@kurko AR code in Rails doesn't require an app to even start successfully. We want to be able to start our apps even in the absence of the database, and then respond to endpoints which do not require DB access successfully. Primarily this is typically our status endpoints. We want to be able to report that the container, and the app are up, but that the DB is down.

If you actually try to execute any endpoints or other codepaths that require DB access you should still get an exception.

[jakehow]

@kurko @mecampbellsoup we should put this in the readme maybe? Associated rails issue -> rails/rails#22154

[kurko]

That makes sense.

[mecampbellsoup]

@kurko @jakehow updated README and PR description

[mecampbellsoup]

@kurko @jakehow GTG?

[jakehow]

@mecampbellsoup while i have no idea how to add the rails tests we could easily add dummy apps for the supported rails versions to confirm this is working from the user's perspective

[jakehow]

@mecampbellsoup also you can run the zipmark-service tests with this branch included to make sure it doesnt break anything

[mecampbellsoup]

@jakehow as, say, fixtures at spec/fixtures/rails-3, rails-4 and now also rails-5 perhaps?

Should it be a rake task or something, e.g. rake test_with_rails_version 3?