Configuration

Applications need to be configured. Information provided during configuration can be—for example— the type of application logging to use, connection strings to databases, hostnames to services such as ESBs or URIs to external APIs, to name just a few.

We can differentiate a few types of configurations, as follows:

• Build time: This is the information needed during the build of the application and/or its Docker image. It needs to be available when we create the Docker images.
• Environment: This is configuration information that varies with the environment in which the application is running—for example, DEVELOPMENT versus STAGING or PRODUCTION. This kind of configuration is applied to the application when a container with the app starts—for example, in production.
• Runtime: This is information that the application retrieves during runtime, such as secrets to access an external API.