title: Runtime Environment

An web application itself should be stateless and has the ability to set its own according to the runtime environment.

Configure Runtime Environment

Egg has two ways to configure runtime environment:

1. Use config/env file, usually we use the build tools to generate this file, the content of this file is just the env value, such as prod.

2. use EGG_SERVER_ENV environment variable to configure.

   The second way will be more commonly used, defining the runtime environment via EGG_SERVER_ENV when you start the application is more convenient, for example, use the code below to start the application in the production environment.

EGG_SERVER_ENV=prod npm start

Access to the runtime environment in Application

Egg provides a variable app.config.env to represent the current runtime environment of application.

Configurations of runtime environment

Different running environment corresponds to different configurations, read Configuration of Config in detail.

Difference from NODE_ENV

Lots of Node.js applications use NODE_ENV to distinguish the runtime environment, but EGG_SERVER_ENV distinguishes the environments much more specific. Generally speaking, there are local environment, test environment, production environment during the application development. In addition to the local development environment and the test environment, other environments are collectively referred to as the Server Environment and their NODE_ENV should be set to production. What’s more, npm will use this variable and will not install the devDependencies when you deploy applications, so production should also be applied.

Default mapping of EGG_SERVER_ENV and NODE_ENV (will generate EGG_SERVER_ENV from NODE_ENV setting if EGG_SERVER_ENV is not specified)

For example, EGG_SERVER_ENV will be set to prod when NODE_ENV is set as production and EGG_SERVER_ENV is not specified.

Customize environment

In normal development process, it’s not limit to these environments mentioned above. So you can customize environment for your development process.

For example, if you want to add SIT (System integration testing) to development process, you can set EGG_SERVER_ENV to sit (also recommend to set NODE_ENV = production), the framework will load config/config.sit.js when launching, and the runtime environment app.config.env will be sit.

Difference from Koa

We are using app.env to distinguish the environments in Koa, and the default value for app.env is process.env.NODE_ENV. But in Egg (and frameworks base on Egg), we put all the configurations in app.config, so we should use app.config.env to distinguish the environments, app.env is no longer used.