title: Runtime Environment

Runtime Environment

There could be all kinds of difference during various stages of a Web application development, but the application itself should be stateless, so EGG provide environment variables to cope with such difference.

EGG framework provides a variable named env for setting up the runtime environment. The env could be used to determine which configuration file should be applied, or you can perform any operations by detecting the env directly.

How to Configure Runtime Environment

There are several ways:

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.
Specify the EGG_SERVER_ENV environment variable.

EGG_SERVER_ENV will be more commonly used, defining the environment variable when you start the application is the simplest way, for example, use the code below to start the application in the production environment.

EGG_SERVER_ENV=prod npm start

How to Use

You can use app.config.env to get the environment variable. You can also load different configuration file for different environment by adding a file like config/config.{env}.js with specified configs, please refer to config for details.

Difference with NODE_ENV

Lots of Node.js applications use NODE_ENV for environment setting, but EGG_SERVER_ENV distinguishes the environments much more specific. Generally speaking, there are local environment, unit test environment, test environment, production environment during the application development. Test and production environment are Server Environment and their NODE_ENV should be set to production , just like how npm make use of NODE_ENV. when you depoly applications in test and production environment, you don't install the devDependencies, so production should 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)

NODE_ENV	EGG_SERVER_ENV	remarks
	local	local development environment
test	unittest	unit test environment
production	prod	production environment

For example, EGG_SERVER_ENV will be set to prod when NODE_ENV is 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 you development process, such as SIT (System integration testing).

Set EGG_SERVER_ENV to sit (also set NODE_ENV = production as recommend), the framework will load config/config.sit.js when lanching, and the runtime environment app.config.env will be sit.

Difference with Koa

We are using app.env to distinguishes the environments in Koa, and app.env defualt to 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 distinguishes the environments, app.env is no logger used.

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