Rails API / Ember-cli web app: what is the conventional workflow?

In the process of building a SPA, we opted for a combination of Rails API and Ember-cli.

From what we understand, the architecture of the app will be the following:

• Rails API will run the back-end of the app, as an API
• Ember-cli will run the front-end of the app, as a front-end MV* framework
• Data will be served by Rails API to Ember-cli with JSON

What does not seem really clear though, is what should be the development workflow?

In other words, should we:

1. Build the back-end (rails models, etc), then build the front-end and finally connect both?
2. Build everything at the same time, but one feature at a time?
3. Go with another option?