C4 Container

%% C4 Level 2 — Containers (the layer model) %% Diagrams as code. Render with any Mermaid renderer. graph TB client(["Application"]) subgraph L1["L1 — Access layer (stateless)"] s3["S3 gateway"] other["FUSE / WebDAV / SDK"] end subgraph L2["L2 — Global control plane (global consensus)"] ns["Namespace DB<br/>(TiDB / TiKV)"] place["Placement service"] reg["Zone registry"] end subgraph L3["L3 — Cross-zone replication (off the data path)"] repl["Replication workers<br/>(NATS JetStream)"] gcust["Global custodians"] end subgraph L4["L4 — Zonal file system (per datacenter)"] meta["Metadata store<br/>(redb / TiKV)"] dserv["D servers<br/>(dumb chunk storage)"] cust["Custodians<br/>(GC / scrub / repair)"] lib["Client library<br/>(EC, commit) — embedded in L1"] end subgraph L5["L5 — Bootstrap & coordination"] etcd["Coordination<br/>(etcd / in-memory)"] end client -->|"request"| s3 s3 -.->|"embeds"| lib s3 -->|"namespace / placement"| place place --> ns place --> reg lib -->|"metadata commit"| meta lib -->|"direct fragment writes (bulk data)"| dserv cust --> meta cust --> dserv repl -->|"copy chunks between zones"| dserv gcust --> ns s3 -.->|"discovery"| etcd cust -.->|"leader election, locks"| etcd dserv -.->|"registration"| etcd