Drupal 8's render pipeline

In Drupal 8, we've significantly improved the way pages are rendered. I will explain the entire render pipeline, which will also cover:

• render caching — blocks and entities are now render cached automatically!
• cache tags — finally we have the cache invalidation system we've always needed!
• assets — only the necessary assets are loaded anymore, thanks to asset dependencies!
• bubbling — rather than relying on global statics that broke caching, we now correctly bubble up all attached metadata — no more frustrations!

But I will also explain what is going to be possible in Drupal 8:

• anonymous page loads: invalidating Varnish/CDNs with perfect precision
• authenticated page loads: not completely regenerated on every page load, but assembled from render cached parts
• alternative render strategies, like Big Pipe

Where relevant, I'll compare with Drupal 7, how you can write Drupal 7 code today that will be easy to upgrade to Drupal 8, and which Drupal 7 backports exist (hint: Big Pipe does exist!).