Putting it all together

The main file prepares a microservice deployment environment via a call to the deployServices helper function. The idea here is to string together the services in such a manner so that tracing a request through the system will yield an interesting trace graph. Let's see how this is done.

First, the helper starts three Provider instances and keeps track of their addresses:

var err error
providerAddrs := make([]string, 3)
for i := 0; i < len(providerAddrs); i++ {
    provider := service.NewProvider(fmt.Sprintf("vendor-%d", i))
    if providerAddrs[i], err = provider.Serve(ctx); err != nil {
        return nil, err
    }
}

Then, it starts an Aggregator instance and sets it up to connect to providers 1 and 2 from the preceding list:

aggr1 := service.NewAggregator("aggr-1", providerAddrs[1:])
aggr1Addr, err := aggr1.Serve(ctx)
if err != nil {
    return nil, err
}

Following that, it instantiates yet another Aggregator type and connects it to provider 0 and the aggregator we just created:

aggr0 := service.NewAggregator("aggr-0", []string{providerAddrs[0], aggr1Addr})
aggr0Addr, err := aggr0.Serve(ctx)
if err != nil {
    return nil, err
}

Finally, a Gateway instance is created with the preceding aggregator as its target and returned to the caller:

return service.NewGateway("api-gateway", aggr0Addr)

The Gateway instance that's returned by the deployServices function is used by runMain to trigger the execution of a quote query that marks the beginning of a new request trace:

func runMain(ctx context.Context) error {
    gw, err := deployServices(ctx)
    if err != nil {
        return err
    }
    defer func() { _ = gw.Close() }()

    res, err := gw.CollectQuotes(ctx, "example")
    if err != nil {
        return err
    }
    fmt.Printf("Collected the following quotes:\n")
    for k, v := range res {
        fmt.Printf("  %q: %3.2f\n", k, v)
    }
    return nil
}

In the following section, we will be hooking up a tracer implementation to our code so that we can capture and visualize the request traces that our code generates.