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Booking service provides a GraphQL API for reservation, confirmation and cancellation operations.

Implementation

Booking Infrastructure Architecture

Booking is comprised of GraphQL API implemented using AppSync, DynamoDB as a database, a booking state machine using Step Functions and Python Lambda functions.

GraphQL API

Booking API provides create, update, read and list (CRUD) operations on Bookings. It also enforces fine-grained authorization to allow booking owners to read and update their bookings only except Admin users.

Configuration

CRUD operations are auto-generated using Amplify off our API schema.

Operation Name Description
query getBookingByStatus Fetches bookings directly from Booking DynamoDB table
mutation processBooking Initiates booking state machine in Step Functions

These auto-generated operations are not currently being used and might change with upcoming improvements. getBooking, listBookings, createBooking, updateBooking, deleteBooking.

type Booking 
    @model(subscriptions: null) 
    @auth(rules: [
      {allow: owner, ownerField: "customer", identityField: "sub", operations: [read, update]},
      {allow: groups, groups: ["Admin"]}
    ])
    @key(name: "ByCustomerStatus", 
        fields: ["customer", "status"],
        queryField: "getBookingByStatus")
{
    id: ID!
    status: BookingStatus!
    outboundFlight: Flight! @connection
    paymentToken: String!
    checkedIn: Boolean
    customer: String
    createdAt: String
    bookingReference: String
}

Booking state machine

Booking state machine handles all operations necessary to create bookings including payment. We use Saga pattern to demonstrate how to implement coordinated transactions, fallback transactions, and dead-letter-queue as part of a state machine.

Process Booking State Machine

Configuration

Access Logs and Server-side caching are not currently being used to prevent additional charges. When Access Logs is enabled, you can use CloudWatch Log Insights to search across fully structured logs on all GraphQL API operations, including resolver and data statistics.

The state machine uses a combination of service integration with DynamoDB and SQS and Lambda functions.

Task Resource Description
Reserve Flight DynamoDB integration Updates Flight table to conditionally decrease seatCapacity field for a given flight
Reserve Booking Reserve Booking function Creates a booking as UNCONFIRMED in the Booking table
Collect Payment Collect Payment function Collects payment from a pre-authorized charge token
Confirm Booking Confirm Booking function Confirms booking and set status to CONFIRMED in the Booking table
Notify Booking Confirmed Notify Booking function Publishes a message to Booking SNS topic

Custom metrics currently emitted to CloudWatch:

Metric Description Dimensions
ColdStart Number of cold start executions function_name, service
InvalidCancellationRequest Number of booking transactions that didn't include booking ID for cancellation service
InvalidConfirmationRequest Number of booking transactions that didn't include booking ID for confirmation service
InvalidNotificationRequest Number of booking transactions that didn't include customer ID and price for notification service
InvalidReservationRequest Number of booking transactions that didn't include customer, charge and flight IDs for reservation service
SuccessfulCancellation Number of successful booking cancellations service
FailedCancellation Number of booking that failed to be cancelled service
SuccessfulBooking Number of bookings confirmed successfully service
SuccessfulNotification Number of booking notifications successfully delivered to customers service
FailedNotification Number of booking notifications that failed to be delivered to customers service
SuccessfulReservation Number of successful booking reservations service
FailedReservation Number of bookings that failed to be reserved service

Parameter store

{env} being a git branch from where deployment originates (e.g. twitch):

Parameter Description
/{env}/service/booking/statemachine/processBooking Process Booking Step Functions State Machine ARN
/{env}/service/booking/messaging/bookingTopic SNS Topic ARN for booking operations

Integrations

Front-end

Booking provides a GraphQL Booking data type and a getBookingByStatus query. Using @key, Booking implements a Global Secondary Index (GS) to fetch booking by customer and status using getBookingByStatus query as opposed to listBookings scan operation.

Flight IDs are stored in Booking table and fetched via @connection that effectively queries a separate table (Flight from Catalog) using a GSI.

Booking front-end integration

Loyalty

See Loyalty integration section for more information

Payment

See Payment integration section for more information

Decisions log

Decision Description Timeframe
State Machine for booking process Primarily to illustrate Saga in practice including handling failed overall executions with a DLQ. This should be simplified after re:Invent 2019, specially booking confirmation. During Twitch season (Apr-Aug '19)
Drop Logging Stack AWS Lambda Powertools Metrics utilize the new Amazon CloudWatch Embedded Metrics Format (EMF) making our custom implementation unnecessary. This also has the benefit of not requiring any additional stack. July 22nd 2020
Introduce Lambda Layers Dependencies are now deployed separately as a Lambda Layer given it's shared with Payment too. This makes new changes to be deployed in seconds from ~2m. July 24th 2020