Using the GetLatestConfiguration API action to read a freeform configuration profile

/*
The example below uses two Amazon AppConfig Data APIs: StartConfigurationSession and GetLatestConfiguration.
For more information about these APIs, see Amazon AppConfig Data.

This class is meant to be used as a singleton to retrieve the latest configuration data from Amazon AppConfig.
This class maintains a cache of the latest configuration data in addition to the configuration token to be
passed to the next GetLatestConfiguration API call.
*/
public class AppConfigApiRetriever {

    /*
     * Set of AppConfig invalid parameter problems that require restarting the configuration session.
     * If the GetLatestConfiguration API call fails with any of these problems (e.g. token is EXPIRED or CORRUPTED),
     * we need to call StartConfigurationSession again to obtain a new configuration token before retrying.
     */
    private final Set<InvalidParameterProblem> SESSION_RESTART_REQUIRED =
            Stream.of(InvalidParameterProblem.EXPIRED, InvalidParameterProblem.CORRUPTED)
                  .collect(Collectors.toSet());

    /*
    Amazon AppConfig Data SDK client used to interact with the Amazon AppConfig Data service.
     */
    private final AppConfigDataClient appConfigData;

    /*
    The configuration token to be passed to the next GetLatestConfiguration API call.
     */
    private String configurationToken;

    /*
    The cached configuration data to be returned when there is no new configuration data available.
     */
    private SdkBytes configuration;

    public AppConfigApiRetriever() {
        this.appConfigData = AppConfigDataClient.create();
    }

    /*
    Returns the latest configuration data stored in Amazon AppConfig.
     */
    public SdkBytes getConfig() {
        /*
        If there is no configuration token yet, get one by starting a new session with the StartConfigurationSession API.
        Note that this API does not return configuration data. Rather, it returns an initial configuration token that is
        subsequently passed to the GetLatestConfiguration API.
         */
        if (this.configurationToken == null) {
            startNewSession();
        }

        GetLatestConfigurationResponse response = null;

        try {
            /*
            Retrieve the configuration from the GetLatestConfiguration API, providing the current configuration token.
            If this caller does not yet have the latest configuration (e.g. this is the first call to GetLatestConfiguration
            or new configuration data has been deployed since the first call), the latest configuration data will be returned.
            Otherwise, the GetLatestConfiguration API will not return any data since the caller already has the latest.
             */
            response = appConfigData.getLatestConfiguration(
                    GetLatestConfigurationRequest.builder()
                                                 .configurationToken(this.configurationToken)
                                                 .build());

        } catch (ResourceNotFoundException e) {
            // Handle resource not found by refreshing the session
            System.err.println("Resource not found — refreshing session and retrying...");
            startNewSession();
            response = appConfigData.getLatestConfiguration(
                    GetLatestConfigurationRequest.builder()
                                                 .configurationToken(this.configurationToken)
                                                 .build());
        } catch (BadRequestException e) {
            // Handle expired or corrupted token by refreshing the session
            boolean needsNewSession = Optional.ofNullable(e.details())
                                              .map(details -> details.invalidParameters()
                                                                     .values()
                                                                     .stream()
                                                                     .anyMatch(val -> SESSION_RESTART_REQUIRED.contains(val.problem())))
                                              .orElse(false);
            if (needsNewSession) {
                System.err.println("Configuration token expired or corrupted — refreshing session and retrying...");
                startNewSession();
                response = appConfigData.getLatestConfiguration(
                        GetLatestConfigurationRequest.builder()
                                                     .configurationToken(this.configurationToken)
                                                     .build());
            } else {
                throw e; // rethrow if it's another kind of bad request
            }
        }

        if (response == null) {
            // Should not happen, but return cached config if no response
            return this.configuration;
        }

        /*
        Save the returned configuration token so that it can be passed to the next GetLatestConfiguration API call.
        Warning: Not persisting this token for use in the next GetLatestConfiguration API call may result in higher
        than expected usage costs.
         */
        this.configurationToken = response.nextPollConfigurationToken();

        /*
        If the GetLatestConfiguration API returned configuration data, update the cached configuration with the returned data.
        Otherwise, assume the configuration has not changed, and return the cached configuration.
         */
        SdkBytes configFromApi = response.configuration();
        if (configFromApi != null && configFromApi.asByteArray().length != 0) {
            this.configuration = configFromApi;
            System.out.println("Configuration contents have changed since the last GetLatestConfiguration call, new contents = "
                    + this.configuration.asUtf8String());
        } else {
            System.out.println("GetLatestConfiguration returned an empty response because we already have the latest configuration");
        }

        return this.configuration;
    }

    /*
    Starts a new session with AppConfig and retrieves an initial configuration token.
     */
    private void startNewSession() {
        StartConfigurationSessionResponse session = appConfigData.startConfigurationSession(req -> req
                .applicationIdentifier("MyDemoApp")
                .configurationProfileIdentifier("MyConfig")
                .environmentIdentifier("Beta"));
        this.configurationToken = session.initialConfigurationToken();
    }
}

# The example below uses two Amazon AppConfig Data APIs: StartConfigurationSession and GetLatestConfiguration.
# For more information about these APIs, see Amazon AppConfig Data.
#
# This class is meant to be used as a singleton to retrieve the latest configuration data from Amazon AppConfig.
# This class maintains a cache of the latest configuration data in addition to the configuration token to be
# passed to the next GetLatestConfiguration API call.
class AppConfigApiRetriever:
    # Set of AppConfig invalid parameter problems that require restarting the configuration session.
    # If the GetLatestConfiguration API call fails with any of these problems (e.g. token is EXPIRED or CORRUPTED),
    # we need to call StartConfigurationSession again to obtain a new configuration token before retrying.
    SESSION_RESTART_REQUIRED = {"EXPIRED", "CORRUPTED"}

    def __init__(self):
        # Amazon AppConfig Data SDK client used to interact with the Amazon AppConfig Data service.
        self.appconfigdata = boto3.client('appconfigdata')

        # The configuration token to be passed to the next GetLatestConfiguration API call.
        self.configuration_token = None

        # The cached configuration data to be returned when there is no new configuration data available.
        self.configuration = None

    # Returns the latest configuration data stored in Amazon AppConfig.
    def get_config(self):
        # If there is no configuration token yet, get one by starting a new session with the StartConfigurationSession API.
        # Note that this API does not return configuration data. Rather, it returns an initial configuration token that is
        # subsequently passed to the GetLatestConfiguration API.
        if not self.configuration_token:
            self._start_new_session()

        response = None
        try:
            # Retrieve the configuration from the GetLatestConfiguration API, providing the current configuration token.
            # If this caller does not yet have the latest configuration (e.g. this is the first call to GetLatestConfiguration
            # or new configuration data has been deployed since the first call), the latest configuration data will be returned.
            # Otherwise, the GetLatestConfiguration API will not return any data since the caller already has the latest.
            response = self.appconfigdata.get_latest_configuration(
                ConfigurationToken=self.configuration_token
            )
        except ClientError as e:
            error_code = e.response.get("Error", {}).get("Code")
            # ResourceNotFoundException — usually means the token/session is invalid or expired
            if error_code == "ResourceNotFoundException":
                print("Resource not found — refreshing session and retrying...")
                self._start_new_session()
                response = self.appconfigdata.get_latest_configuration(
                    ConfigurationToken=self.configuration_token
                )
            # BadRequestException — check if it's expired or corrupted token
            elif error_code == "BadRequestException":
                details = e.response.get("Error", {}).get("Details", {}) or {}
                invalid_params = details.get("InvalidParameters", {}) or {}
                needs_new_session = any(
                    param.get("Problem") in self.SESSION_RESTART_REQUIRED
                    for param in invalid_params.values()
                )
                if needs_new_session:
                    print("Configuration token expired or corrupted — refreshing session and retrying...")
                    self._start_new_session()
                    response = self.appconfigdata.get_latest_configuration(
                        ConfigurationToken=self.configuration_token
                    )
                else:
                    raise
            else:
                raise

        if response is None:
            # Should not happen, but return cached config if no response
            return self.configuration

        # Save the returned configuration token so that it can be passed to the next GetLatestConfiguration API call.
        # Warning: Not persisting this token for use in the next GetLatestConfiguration API call may result in higher
        # than expected usage costs.
        self.configuration_token = response['NextPollConfigurationToken']

        # If the GetLatestConfiguration API returned configuration data, update the cached configuration with the returned data.
        # Otherwise, assume the configuration has not changed, and return the cached configuration.
        config_stream = response.get('Configuration')
        if config_stream:
            config_from_api = config_stream.read()
            if config_from_api:
                self.configuration = config_from_api
                print(
                    'Configuration contents have changed since the last GetLatestConfiguration call, new contents = '
                    + self.configuration.decode('utf-8', errors='ignore')
                )
            else:
                print('GetLatestConfiguration returned an empty response because we already have the latest configuration')

        return self.configuration

    # Starts a new session with AppConfig and retrieves an initial configuration token.
    def _start_new_session(self):
        session = self.appconfigdata.start_configuration_session(
            ApplicationIdentifier='MyDemoApp',
            ConfigurationProfileIdentifier='MyConfig',
            EnvironmentIdentifier='Beta'
        )
        self.configuration_token = session['InitialConfigurationToken']

/*
The example below uses two Amazon AppConfig Data APIs: StartConfigurationSession and GetLatestConfiguration.
For more information about these APIs, see Amazon AppConfig Data
.

This class is meant to be used as a singleton to retrieve the latest configuration data from Amazon AppConfig.
This class maintains a cache of the latest configuration data in addition to the configuration token to be
passed to the next GetLatestConfiguration API call.
*/
class AppConfigApiRetriever {
  constructor() {
    /*
    Amazon AppConfig Data SDK client used to interact with the Amazon AppConfig Data service.
     */
    this.appconfigdata = new AppConfigDataClient();

    /*
    The configuration token to be passed to the next GetLatestConfiguration API call.
     */
    this.configurationToken = null;

    /*
    The cached configuration data to be returned when there is no new configuration data available.
     */
    this.configuration = null;
  }

  async startSession() {
    /*
    Starts a new session with the StartConfigurationSession API to get an initial configuration token.
    */
    const session = await this.appconfigdata.send(
      new StartConfigurationSessionCommand({
        ApplicationIdentifier: "MyDemoApp",
        ConfigurationProfileIdentifier: "MyConfig",
        EnvironmentIdentifier: "Beta"
      })
    );
    this.configurationToken = session.InitialConfigurationToken;
  }

  /*
  Returns the latest configuration data stored in Amazon AppConfig.
   */
  async getConfig() {
    /*
    If there is no configuration token yet, get one by starting a new session with the StartConfigurationSession API.
    Note that this API does not return configuration data. Rather, it returns an initial configuration token that is
    subsequently passed to the GetLatestConfiguration API.
    */
    if (!this.configurationToken) {
      await this.startSession();
    }

    let response;
    try {
      /*
      Retrieve the configuration from the GetLatestConfiguration API, providing the current configuration token.
      If this caller does not yet have the latest configuration (e.g. this is the first call to GetLatestConfiguration
      or new configuration data has been deployed since the first call), the latest configuration data will be returned.
      Otherwise, the GetLatestConfiguration API will not return any data since the caller already has the latest.
      */
      response = await this.appconfigdata.send(
        new GetLatestConfigurationCommand({
          ConfigurationToken: this.configurationToken
        })
      );
    } catch (err) {
      /*
      Add session restart logic — if the token is invalid or expired, restart the session and try once more.
      */
      if (err.name === "ResourceNotFoundException" || err.name === "BadRequestException") {
        console.warn(
          "Configuration token invalid or expired. Restarting session..."
        );
        await this.startSession();
        response = await this.appconfigdata.send(
          new GetLatestConfigurationCommand({
            ConfigurationToken: this.configurationToken
          })
        );
      } else {
        throw err;
      }
    }

    /*
    Save the returned configuration token so that it can be passed to the next GetLatestConfiguration API call.
    Warning: Not persisting this token for use in the next GetLatestConfiguration API call may result in higher
    than expected usage costs.
    */
    this.configurationToken = response.NextPollConfigurationToken;

    /*
    If the GetLatestConfiguration API returned configuration data, update the cached configuration with the returned data.
    Otherwise, assume the configuration has not changed, and return the cached configuration.
    */
    const configFromApi = response.Configuration
      ? await response.Configuration.transformToString()
      : null;

    if (configFromApi) {
      this.configuration = configFromApi;
      console.log(
        "Configuration contents have changed since the last GetLatestConfiguration call, new contents = " +
          this.configuration
      );
    } else {
      console.log(
        "GetLatestConfiguration returned an empty response because we already have the latest configuration"
      );
    }

    return this.configuration;
  }
}