nginx configuration cache updates, back-end fault, allowing the use of expired cache

1. Configure cache updates, back-end fault, allowing the use of expired cache

# Cache configuration, can not be removed
proxy_cache_path proxy_cache Levels. 1 =: 2 = page_cache keys_zone: 512M MAX_SIZE = inactive = 1M 80g use_temp_path = OFF;
# update cache configuration, the rear end of the fault, allowing the use of outdated cache
proxy_cache_use_stale error timeout invalid_header updating http_500 http_502 http_503 http_504 ;