Calculator Madness

Microservice playground with a calculator theme. This project does nothing and is not used for anyting other than learning.

calc-demo.mp4

So what is it?

This is a small application that takes text input (an equation) and spends an inordinate amount of time counting how many chars the equation consists of. The complexity lies in the backend which has a microservice-based architecture that facilitates async message handling between calculator and viewer. Each connected client (browser) is connected using websocket making it possible to receive continous progress messages in the UI.

The system consists of the following components:

1. viewer is the front facing UI server which establishes websocket connections to the clients, does GRPC calls to the calculator and receives results and progress messages over nsq. Because a single viewer instance might serve multiple websocket connections, it is necessary to pass along a connection id through the backend calls.
2. nsq is an instance of the NSQ(New Simple Queue) message queue implemented as a shared Go module. It contains a producer and a consumer that is reused across services. The consumer is generic on the message interface type. Due to the uniqueness of each websocket connection, a unique topic and consumer is used per viewer instance.
3. calculator is the core business logic which amounts to return len(equation). However, the service features a GRPC interface and will publish equation processing results to nsq.

Usage

Run all services in docker

make build run

Make a query against the calculator

grpcurl -plaintext -d '{"client_id":"<cid>", "equation":{"id":"<eid>", "value":"1+1"}, "result_topic":"<topic>"}' localhost:8000 calculator.CalculationService/Run

List all grpc endpoints of the calculator

grpcurl --plaintext localhost:8000 list

Debugging lookupd / running locally

• If using nsqlookupd it can be necessary to set broadcast address of nsqd to be able to run nsq in docker next to other services running on the host e.g. for debugging. See: nsqio/go-nsq#69

command: /nsqd --lookupd-tcp-address=nsqlookupd:4160 #--broadcast-address=127.0.0.1 #example for debugging locally

Details

Overall system architecture

Component diagram showing the essential modules and their general interaction.

flowchart LR
    subgraph viewer
        http-->static
        http-->manager
        http-->templates
        subgraph websocket
            manager-->clients
            clients-->router
        end
    end

    subgraph calculator
        grpc--create calculation-->calc
    end

    subgraph nsq
        producer-.enqueue.->queue
        consumer-.dequeue.->queue
    end

    browser-->http
    calc--async-->producer
    manager--async-->consumer
    router--sync-->grpc

Loading

Interaction between calculator and nsq

Sequence diagram showing interaction between calculator and nsq when calculations are created. The calculator service takes requests on a GRPC endpoint but returns results asynchronously over nsq.

sequenceDiagram
    participant cli as Client
    participant cal as Calculator
    participant nsq as NSQ

    cli->>cal: RunCalculation(id)
    cal-->>cli: CalcRecieved(id)
    Note over cal: Calculator maintains state of calculations

    %%cal--)nsq: SendCalcStarted(id)
    loop calc in progress
        cal-)nsq: SendCalcProgress(id)
    end
    cal-)nsq: SendCalcEnded(id)

    Note over nsq, cli: Client listens and receives messages on topics

    nsq--)cli: CalcProgress()
    nsq--)cli: CalcEnded()

Loading

Creating a new calculation in the viewer

Sequence diagram of how viewer interacts with the backend when a new calculation is created.

sequenceDiagram
    participant B as Browser
    participant W as Viewer
    participant C as Calculator
    participant Q as NSQ

    B->>W: New equation

    Note over W: Keep state of calculations

    W-->>B: Create new calc <ID>

    W->>+C: Start calculation

    loop while in progress
        C-)Q: Enqueue calc progress <ID>
        Q--)W: Return calc progress <ID>
        W-->>B: Send calc progress <ID> event
    end

    C->>-Q: Enqueue calc done <ID>
    Q--)W: Return calc done <ID>
    W-->>B: Send calc done <ID> event

Loading

Handling calculation progress and results concurrently

Sequence diagram showing the interaction of the concurrent handling of equations in the CalculatorService.

sequenceDiagram
    participant CL as Viewer
    participant GR as GRPCServer
    participant CS as CalculatorService
    participant EP as EquationProcessor
    participant RN as ResultNotifier

    CL->>GR: Request to solve equation
    GR->>CS: Call Solve(eq)
    CS->>EP: Send equation to intake chan
    CS-->>CL: Return OK grpc response

    Note over CL, RN: Equation results are received on queue

    loop for N=len(equation) seconds
        EP-->>CS: New progress msg
        CS->>RN: Post progress msg to notifier
        RN-->>CL: Return progress response to client
    end


    EP-->>CS: Ended equation msg
    CS->>RN: Post ended equation msg to notifier
    RN-->>CL: Return ended equation response to client

Loading