Storage and Content Delivery (OSS, CDN)
Core concepts
Object Storage Service (OSS) stores objects in buckets, each bound to a region and globally unique in name. Understand storage classes: Standard, Infrequent Access (IA), Archive, and Cold Archive - each trades retrieval latency and minimum storage duration for price. Know redundancy: locally redundant (LRS) vs zone-redundant (ZRS).
Master access control: bucket ACLs (private, public-read, public-read-write), bucket policies, and RAM policies. Pre-signed URLs grant time-limited access to private objects without exposing credentials.
Versioning protects against overwrites and deletes; lifecycle rules transition objects between classes and expire them. Cross-region replication copies objects to another bucket for DR.
Alibaba Cloud CDN caches static content at edge nodes. You configure an accelerated domain, origin (OSS bucket or ECS), and caching rules. HTTPS, referer anti-leech, and URL signing are the security levers.
Traps
- Archive classes have minimum storage durations and retrieval fees; questions that say "instantly readable" are wrong for archive.
- A public-read bucket exposes listing/data to the internet - a common exam "security mistake."
- CDN does not replace OSS; it fronts it. Cache invalidation is manual or TTL-based.
Rule of thumb
Static assets served to many users → OSS origin + CDN + HTTPS. Sensitive files shared temporarily → private bucket + pre-signed URL. Long-term compliance archive → Archive class + lifecycle rule.