Step 6: Retrieving the configuration - AWS AppConfig

Step 6: Retrieving the configuration

Your application retrieves configuration data by first establishing a configuration session using the StartConfigurationSession API action. Your session's client then makes periodic calls to GetLatestConfiguration to check for and retrieve the latest data available.

When calling StartConfigurationSession, your code sends the following information:

  • Identifiers (ID or name) of an AWS AppConfig application, environment, and configuration profile that the session tracks.

  • (Optional) The minimum amount of time the session's client must wait between calls to GetLatestConfiguration.

In response, AWS AppConfig provides an InitialConfigurationToken to be given to the session's client and used the first time it calls GetLatestConfiguration for that session.

Important

This token should only be used once in your first call to GetLatestConfiguration. You must use the new token in the GetLatestConfiguration response (NextPollConfigurationToken) in each subsequent call to GetLatestConfiguration.

When calling GetLatestConfiguration, your client code sends the most recent ConfigurationToken value it has and receives in response:

  • NextPollConfigurationToken: the ConfigurationToken value to use on the next call to GetLatestConfiguration.

  • NextPollIntervalInSeconds: the duration the client should wait before making its next call to GetLatestConfiguration. This duration may vary over the course of the session, so it should be used instead of the value sent on the StartConfigurationSession call.

  • The configuration: the latest data intended for the session. This may be empty if the client already has the latest version of the configuration.

Important

Note the following important information.

  • The StartConfigurationSession API should only be called once per application, environment, configuration profile, and client to establish a session with the service. This is typically done in the startup of your application or immediately prior to the first retrieval of a configuration.

  • The InitialConfigurationToken and NextPollConfigurationToken expire after 24 hours. If a GetLatestConfiguration call uses an expired token, the system returns BadRequestException.

Retrieving a configuration example

The following AWS CLI example demonstrates how to retrieve configuration data by using the AWS AppConfig Data StartConfigurationSession and GetLatestConfiguration API actions. The first command starts a configuration session. This call includes the IDs (or names) of the AWS AppConfig application, the environment, and the configuration profile. The API returns an InitialConfigurationToken used to fetch your configuration data.

aws appconfigdata start-configuration-session \ --application-identifier application_name_or_ID \ --environment-identifier environment_name_or_ID \ --configuration-profile-identifier configuration_profile_name_or_ID

The system responds with information in the following format.

{ "InitialConfigurationToken": initial configuration token }

After starting a session, use InitialConfigurationToken to call GetLatestConfiguration to fetch your configuration data. The configuration data is saved to the mydata.json file.

aws appconfigdata get-latest-configuration \ --configuration-token initial configuration token mydata.json

The first call to GetLatestConfiguration uses the ConfigurationToken obtained from StartConfigurationSession. The following information is returned.

{ "NextPollConfigurationToken" : next configuration token, "ContentType" : content type of configuration, "NextPollIntervalInSeconds" : 60 }

Subsequent calls to GetLatestConfiguration must provide NextPollConfigurationToken from the previous response.

aws appconfigdata get-latest-configuration \ --configuration-token next configuration token mydata.json
Important

Note the following important details about the GetLatestConfiguration API action:

  • The GetLatestConfiguration response includes a Configuration section that shows the configuration data. The Configuration section only appears if the system finds new or updated configuration data. If the system doesn't find new or updated configuration data, then the Configuration data is empty.

  • You receive a new ConfigurationToken in every response from GetLatestConfiguration.

  • We recommend tuning the polling frequency of your GetLatestConfiguration API calls based on your budget, the expected frequency of your configuration deployments, and the number of targets for a configuration.