Dynamic Configuration for Cloud Native Swift Services in Kubernetes

1// Providers are initialized asynchronously: EnvironmentVariablesProvider reads
2// the process environment and .env file at initialization, so the initialization is asynchronous.
3async let staticProviders: [(any ConfigProvider)] = [
4   CommandLineArgumentsProvider(),
5   EnvironmentVariablesProvider(),
6   EnvironmentVariablesProvider(environmentFilePath: ".env", allowMissing: true),
7   InMemoryProvider(values: [
8       "log.level": "info",
9       "config.filePath": "/etc/config/appsettings.yaml",
10       "config.pollIntervalSeconds": 15,
11       "http.serverName": "my-service",
12   ]),
13]
14
15let initConfig = ConfigReader(providers: staticProviders)
16let logLevel = initConfig.string(
17    forKey: "log.level",
18    as: Logger.Level.self,
19    default: .info
20)
21let httpConfig = initConfig.scoped(to: "http") // reads "http.port", "http.host" as just "port", "host"
22let reloadingProvider = try await ReloadingFileProvider<YAMLSnapshot>(
23   config: initConfig.scoped(to: "config")
24)
25let config = ConfigReader(
26   providers: [reloadingProvider] + staticProviders
27)

1struct ConfigWatchReporter: Service {
2   let config: ConfigReader
3   let logger: Logger
4   func run() async throws {
5       try await self.config.scoped(to: "app")
6       .watchString(forKey: "name", default: "unset") { updates in
7           for try await update in updates.cancelOnGracefulShutdown() {
8               logger.info("Received a configuration change: \(update)")
9           }
10       }
11   }
12}
13let configReporter = ConfigWatchReporter(config: config, logger: logger)

1let app = Application(
2   router: router,
3   configuration: ApplicationConfiguration(reader: config.scoped(to: "http")),
4   services: [
5       reloadingProvider,
6       configReporter,
7   ],
8   logger: logger
9)