idempotender

Middy middleware for configuring AWS Lambda Functions using AWS AppConfig.

You can automatically enable/disable a function based on a certain feature flag, or in more complex scenarios you can get the full configuration from request.context.appconfiger for more advanced tweaks in your function.

Usage

• npm install --save @appconfiger/middy

Example: Enable/disable a Lambda function based on feature flag state

• In this example the function will automatically refuse all requests if the feature flag 'myFunctionFlag' is disabled or inexistent in AppConfig.

• Create Lambda function

import appConfigerMiddy from '@appconfiger/middy';

const handler = middy((event, context) => {
  console.log(`Running function on ${new Date()}`);
  return { message: `This function was run on ${new Date()}` };
});

handler.use(
  appConfigerMiddy({
    applicationId: 'aaaaa', //from AppConfig
    configurationProfileId: 'bbbbb', //from AppConfig
    environmentId: 'ccccc', //from AppConfig
    featureFlag: 'myFunctionFlag',
  }),
);

Reference

Configuration

const idem = appConfigerMiddy({
  applicationId: '[APP ID IN APPCONFIG]',
  configurationProfileId: '[CONFIG PROFILE ID IN APPCONFIG]',
  environmentId: '[ENV ID IN APPCONFIG]',
  featureFlag: '[FLAG NAME IN APP CONFIG]',
  pollingInterval: 300,
}

• Config attributes

  • applicationId

    • Application name as defined in AppConfig. Required.

  • configurationProfileId

    • Configuration Profile Id as defined in AppConfig. Required.

  • environmentId

    • Environment Id as defined in AppConfig. Required.

  • featureFlag

    • Feature flag name. Required.
    • This Lambda function will be enabled only if there is a enabled feature flag with this same name in AppConfig
    • If you use an empty string as the name, this function will be always enabled and you can get AppConfig configurations from context.appconfiger for more complex checks.

  • pollingInterval

    • Interval in seconds for checking if there is a newer configuration in AppConfig
    • During this period the latest version of the configuration will be available
    • The polling is performed in background, so your function won't wait for the polling to finish before being run
    • Defaults to 300 (5 minutes)

Handler context

When your function is called, you can access the attribute appconfiger in the context of the handler for accessing the complete configuration object.

• If the configuration in AppConfig is of type 'application/json', which is the most common situation, you will have a parsed object in the context.

• When using the 'feature flag' type of configuration in AppConfig, implicitly you are using 'application/json' and in this attribute you will have access to the complete list of feature flags and its inner attributes (as you configured in AppConfig). For example:

context.appconfiger >>>
  {
    featureFlag1: {
      enabled: true,
      customData1: 123,
    },
    featureFlag2: {
      enabled: false,
    },
  };