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State externalization principle

The State externalization principle is a design philosophy in software engineering that dictates application state should be stored outside of the application's own runtime memory^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md]. Instead of relying on local storage mechanisms—such as writing to local files—the application should persist data to an external service^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md].

Core Purpose

The primary goal of this principle is to ensure data resilience and availability in distributed environments^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md].

If an application maintains state internally (e.g., on a local disk) and subsequently crashes, that state may be lost or become inaccessible^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md]. By externalizing state, the data remains intact even if the application instance fails, allowing for recovery or scaling by simply spinning up a new instance that connects to the same external data source^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md].

Challenges of Local State

Adhering to the principle addresses specific architectural challenges associated with local file storage:

  • Concurrency Issues: Using a local file as storage can be problematic if multiple instances of the service are deployed, as they may attempt to write to the same file simultaneously^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md].
  • Data Loss: It is crucial to keep state out of the application to prevent data loss in the event of a crash^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md].

Implementation

In practice, externalizing state involves replacing local I/O operations with connections to external databases or caches^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md].

For example, an application might initially read and write records to a local json file^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md]. To apply the state externalization principle, the code is refactored to interface with an external database like Redis^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md]. This requires the application to manage connection details (such as address, port, and credentials) via environment variables or configuration management, allowing the state to live independently of the application lifecycle^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md].

  • [[Redis]]
  • [[Scalability]]
  • [[Microservices]]
  • [[Persistence]]

Sources

^[400-devops__09-Scripting-Language__golang__introduction__part-5.database.redis__readme.md]