Pastebin — Detailed

flowchart TB
  subgraph Client
    BR([Browser])
    CLI[CLI / API]
  end

  subgraph Edge
    DNS[DNS]
    CDN[CDN / Edge cache]
    LB[L7 LB]
    WAF[WAF + abuse]
  end

  subgraph App[App Tier]
    GW[API Gateway]
    CRT[Create Service]
    READ[Read Service]
    DEL[Delete / Expire]
    SYN[Syntax highlighter<br/>server-side]
    AUTH[Auth - opt]
  end

  subgraph ID[ID generation]
    SF[Snowflake / KGS]
    B62[Base62 encode<br/>8 chars]
  end

  subgraph Storage
    META[(Metadata SQL<br/>paste id, owner, expiry, lang)]
    BLOB[(Object store S3 / GCS<br/>raw paste body)]
    CACHE[(Redis hot pastes)]
  end

  subgraph Async
    Q[[Kafka events<br/>create / view / delete]]
    SC([Expiry sweeper<br/>cron])
    ANL[Analytics<br/>views, languages]
    AB([Abuse scanner<br/>secret detection])
  end

  subgraph Obs
    M[Metrics] 
    L[Logs] 
    T[Traces]
  end

  BR --> DNS --> CDN --> LB --> WAF --> GW
  CLI --> DNS
  GW --> CRT
  GW --> READ
  GW --> DEL
  CRT --> SF --> B62
  CRT --> META
  CRT --> BLOB
  READ --> CACHE
  CACHE -. miss .-> BLOB
  READ --> META
  READ --> SYN
  DEL --> META
  DEL --> BLOB
  SC -.expire.-> META
  SC -.delete.-> BLOB
  CRT --> Q
  Q --> ANL
  Q --> AB
  AB -.flag.-> META
  App -.metrics.-> M

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class BR client;
    class DNS,CDN,LB,WAF,GW edge;
    class CLI,CRT,READ,DEL,SYN,AUTH,B62,ANL service;
    class SF,META datastore;
    class CACHE cache;
    class Q queue;
    class SC,AB compute;
    class BLOB storage;
    class M,L,T obs;

Storage choice

• Body in object store (S3) — keyed by paste id; cheap, durable.
• Metadata in SQL (or DynamoDB) for indexing by owner, recent, expiry.
• Hot pastes cached in Redis as id → body (TTL 1 hr).

Expiry

• Either: (a) explicit cron sweeping expires_at < now, (b) S3 lifecycle policy delete.
• Soft-delete then GC for undo window.

Privacy modes

• Public / Unlisted / Private (password-protected).
• For private: store paste encrypted with key derived from URL fragment (zero-knowledge — server can't read).

Anti-abuse

• Scan content for API keys, PII; rate-limit per IP.
• Captcha + honeypot for anonymous create.

Glossary & fundamentals

Concepts referenced in this design. Each row links to its canonical page; the tag column shows whether it is a high-level (HLD) or low-level (LLD) concept.

Tag	Concept	What it is	Page
HLD	Load balancer / GSLB	L4/L7 traffic distribution and failover	load-balancer
HLD	CDN	edge caching for static assets	cdn
HLD	API gateway / BFF	single ingress, auth, rate limit, routing	api-gateway
HLD	Pub/Sub & message brokers	topics, consumer groups, delivery semantics	pub-sub-pattern
HLD	Observability	metrics, logs, traces, SLOs	observability
HLD	Search internals	inverted index, BM25, embeddings, ANN	search-internals