C4 Container — service topology & protocols

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flowchart TB
    %% ===== C4-Container style diagram =====
    %% Notation: rectangle = Container (deployable unit), cylinder = Data store,
    %% stadium = External system, hexagon = Person. Protocol annotations on edges.

    %% ---------- People / External ----------
    user(["fa:fa-user Customer
browser + mobile"]):::person
    stripe{{"Stripe
external PSP"}}:::ext
    email{{"SES / SendGrid
transactional email"}}:::ext

    %% ---------- Edge ----------
    subgraph edge[" Edge Tier "]
        direction TB
        alb["ALB + AWS WAF
HTTPS · TLS via ACM"]:::edge
        kong["kong-gateway
Kong OSS
JWT · rate-limit · CORS · CSRF"]:::svc
    end

    %% ---------- Frontend ----------
    subgraph fe[" Frontend "]
        direction TB
        client[["client
Next.js 16 (App Router) · TS
SSR + Server Actions"]]:::svc
    end

    %% ---------- GraphQL Federation ----------
    subgraph gql[" GraphQL Federation "]
        direction TB
        router[["apollo-router
Apollo Router v2.1
supergraph gateway"]]:::svc
    end

    %% ---------- Identity domain ----------
    subgraph identity[" Identity "]
        direction TB
        auth[["auth-service
NestJS 10 · Node 24
signup · login · JWT"]]:::svc
        user_svc[["user-service
NestJS 10 · Node 24
profile · prefs · billing"]]:::svc
        auth_db[(auth_db
RDS PostgreSQL)]:::db
        user_db[(user_db
RDS PostgreSQL)]:::db
        auth --- auth_db
        user_svc --- user_db
    end

    %% ---------- Catalog domain ----------
    subgraph catalog[" Catalog "]
        direction TB
        ticket[["ticket-service
Go 1.23 · Echo v4 · gqlgen
quota · reserve · finalize"]]:::svc
        venue[["venue-service
Go 1.23 · Echo v4 · gqlgen
seating plan · seat holds · SSE"]]:::svc
        ticket_db[(ticket_db
MongoDB 7)]:::db
        venue_db[(venue_db
RDS PostgreSQL)]:::db
        venue_redis[(ElastiCache Redis
seat hold hot path)]:::db
        ticket --- ticket_db
        venue --- venue_db
        venue --- venue_redis
    end

    %% ---------- Transaction domain ----------
    subgraph txn[" Transaction "]
        direction TB
        order[["order-service
Java 21 · Spring Boot 4
saga orchestrator · outbox"]]:::svc
        payment[["payment-service
NestJS 10 · Node 24
Stripe intents · webhooks"]]:::svc
        expiration[["expiration-service
Go 1.23
Redis ZSET timers"]]:::svc
        order_db[(order_db
RDS PostgreSQL
+ outbox)]:::db
        payment_db[(payment_db
RDS PostgreSQL)]:::db
        redis[(ElastiCache Redis
timers · cache · idempotency)]:::db
        order --- order_db
        payment --- payment_db
        expiration --- redis
    end

    %% ---------- Messaging ----------
    subgraph bus[" Async Messaging "]
        direction LR
        kafka{{"Amazon MSK · Kafka
CloudEvents v1.0 envelopes"}}:::mq
        sr[["Glue Schema Registry
Avro/JSON Schema"]]:::mq
        kafka --- sr
    end

    %% ===== Synchronous edges (HTTP/gRPC) =====
    user -- HTTPS --> alb
    alb --> kong
    kong -- SSR --> client
    kong -- "REST /auth/*" --> auth
    kong -- "REST /users/*" --> user_svc
    kong -- "REST /tickets/*" --> ticket
    kong -- "REST /venues/*" --> venue
    kong -- "REST /orders/*" --> order
    kong -- "REST /payments/*" --> payment
    kong -- "Stripe webhook" --> payment
    kong -- "POST /graphql" --> router

    %% Apollo Federation subgraph edges
    router -. "subgraph" .-> auth
    router -. "subgraph" .-> user_svc
    router -. "subgraph" .-> ticket
    router -. "subgraph" .-> venue
    router -. "subgraph" .-> order
    router -. "subgraph" .-> payment

    %% gRPC inside the mesh
    order == "gRPC ReserveQuota / Finalize / Release" ==> ticket
    order == "gRPC ReserveHeldSeats / AutoAssign / Finalize" ==> venue
    ticket == "gRPC GetSeatingPlan" ==> venue
    auth  -. "JWKS (pub key)" .-> kong
    client -- "server-to-server API" --> kong

    %% External
    payment -- "HTTPS PaymentIntents" --> stripe
    payment -- "email receipt" --> email

    %% ===== Asynchronous edges (Kafka) =====
    order -- "produces
orders.order.{created,cancelled,completed}" --> kafka
    kafka -- "consumes" --> ticket
    kafka -- "consumes" --> venue
    kafka -- "consumes" --> expiration
    kafka -- "consumes" --> payment
    expiration -- "produces
expiration.order.expiration_complete" --> kafka
    kafka -- "consumes" --> order
    ticket -- "produces
tickets.ticket.{created,updated}" --> kafka

    %% ===== Styles =====
    classDef svc fill:#FF9900,stroke:#232F3E,stroke-width:1.5px,color:#232F3E;
    classDef db fill:#1A73E8,stroke:#232F3E,stroke-width:1.5px,color:#FFFFFF;
    classDef mq fill:#7D3C98,stroke:#232F3E,stroke-width:1.5px,color:#FFFFFF;
    classDef edge fill:#232F3E,stroke:#232F3E,stroke-width:1.5px,color:#FFFFFF;
    classDef ext fill:#7AA116,stroke:#232F3E,stroke-width:1.5px,color:#FFFFFF;
    classDef person fill:#FDF6E3,stroke:#232F3E,stroke-width:1.5px,color:#232F3E;