unfortunately, doing something like the following creates a race condition:

environment: [{
    name: "APP_HOSTNAME",
    value: pulumi.output(pulumi.all([myFirstFargateService.id, myFirstServiceRegistryService.id])
        .apply(([myFirstFargateServiceId, myFirstServiceRegistryServiceId]) => {
            serviceDiscovery.listInstances({ServiceId: myFirstServiceRegistryServiceId}, function (err, data) {
                if (err) {
                    throw err;
                } else {
                    return data.Instances[0].Attributes["AWS_INSTANCE_IPV4"];
                }
            });
        }))
}]