Airbnb / Booking.com — Detailed

flowchart TB
  subgraph Apps
    GUEST[Guest]
    HOST[Host]
  end

  subgraph Edge
    CDN
    GW
  end

  subgraph Listing
    LSVC[Listing Service]
    LDB[(Listings)]
    IMG[Images / S3]
    DESC[Descriptions / translations]
  end

  subgraph Search[Search & Discovery]
    SRCH[Search API]
    IDX[(Search index<br/>geo + filters)]
    REC[Ranking + personalization]
    HMAP[Map tile aggregation]
  end

  subgraph Avail[Availability & Pricing]
    AV[Availability Service]
    AVDB[(Calendar per listing)]
    PRICE[Pricing engine<br/>dynamic + smart pricing]
    BLOCK[Manual blocks]
  end

  subgraph Book[Booking]
    QUOTE[Quote service<br/>price + fees + taxes]
    BSVC[Booking Service]
    BDB[(Bookings)]
    SAGA([Saga: hold-pay-confirm])
    PAYSVC[Payment]
    PG((Payment provider))
  end

  subgraph Comm
    MSG[Guest-host messaging]
    REV[Reviews]
  end

  subgraph Trust
    ID[ID verification]
    SAFE[Fraud & risk]
    DISP[Resolution / refund]
  end

  subgraph Notif
    EMAIL
    PUSH
    SMS
  end

  GUEST --> CDN --> GW
  HOST --> CDN
  GW --> Listing
  GW --> Search
  Search --> Avail
  GW --> Book
  Book --> Avail
  Book --> PAYSVC --> PG
  Book --> Comm
  Trust --- Book
  Notif --- Book

    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 GUEST,HOST,LSVC,DESC,SRCH,REC,HMAP,AV,PRICE,BLOCK,QUOTE,BSVC,PAYSVC,MSG,REV,ID,SAFE,DISP service;
    class LDB,IDX,AVDB,BDB datastore;
    class SAGA compute;
    class IMG storage;
    class PG external;

Availability correctness

• Per-listing calendar: (date, state) with states available / blocked / pending / booked.
• Booking flow holds date range with TTL, charges card, then confirms.
• Optimistic CAS on date range: detect conflict at commit.

Search relevance

• Personalized ranker combining price, quality, location, host responsiveness, time-to-respond.
• Geo + filter index keyed by S2 cell + amenities posting lists.

Pricing

• Dynamic / smart pricing per night based on demand, lead time, weekday, events.

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	CDN	edge caching for static assets	cdn
HLD	Distributed transactions	2PC, TCC, sagas, outbox/inbox	distributed-transactions
HLD	Geo indexing	Geohash, Quadtree, S2, H3, R-tree	geo-indexing
LLD	Concurrency primitives	mutex, semaphore, RW lock, atomic, CAS	concurrency-primitives