Drupal 8 Cache contexts

Drupal 8 shiped with a powerfull cache API able to set cache according to a context. correct usage of this cache improve the site preformence greatly.

https://www.drupal.org/docs/8/api/cache-api/cache-contexts
https://www.drupal.org/node/2451661

Cache contexts

cookies:NAME
headers:NAME
ip
languages:TYPE
request_format
route.book_navigation
route.menu_active_trails:MENU_NAME
route.name
session.exists
theme
timezone
url.path.is_front
url.path.parent
url.query_args:KEY
url.query_args.pagers:PAGER_ID
url.site
user.is_super_user
user.node_grants:OPERATIONS
user.permissions
user.roles:ROLE

Example 1 - URL :

$output['#cache']['max-age'] = 3600; // 3600 = 1h
$output['#cache']['contexts'] = ['url'];

Example 2 - User :

$output['#cache']['max-age'] = 3600; // 3600 = 1h
$output['#cache']['contexts'] = ['user'];