How do you pass custom environment variable on Amazon Elastic Beanstalk (AWS EBS)?

In the 2016 Java8 Tomcat8 AMI, ElasticBeanstalk fails to set environment variables from the web configuration. They are really setting jvm -D properties instead.

-- "The following properties are passed into the application as environment variables. Learn more."

This statement is incorrect for the Java Tomcat ami. Amazon does not set these as environment variables. They are set as System properties passed on the command line to Tomcat as a -D property for jvm. The method in Java to get environment variables is not the same for getting a property. System.getenv vs System.getProperty

I ssh'd into the box and verified that the environment variable was never set. However, in the tomcat logs I can see the -D property is set.

I've changed my code to check for both locations now as a workaround.

AWS will interpret CloudFormation template strings in your environment variables. You can use this to access information about your EB environment inside your application:

In the AWS web interface the following will be evaluated as the name of your environment (note the back ticks):

`{ "Ref" : "AWSEBEnvironmentName" }`

Or, you can use an .ebextensions/*.config and wrap the CloudFormation template in back ticks (`):

{
  "option_settings": [
    {
      "namespace": "aws:elasticbeanstalk:application:environment",
      "option_name": "ENVIRONMENT_NAME",
      "value": "`{ \"Ref\" : \"AWSEBEnvironmentName\" }`"
    }
  ]
}

Only 5 values is limiting, or you may want to have a custom environment variable name. You can do this by using the configuration files. Create a directory at the root of your project called

.ebextensions/

Then create a file called environment.config (this file can be called anything but it must have the .config extension) and add the following values

option_settings:
  - option_name: CUSTOM_ENV
    value: staging

After you deploy your application you will see this new value under Environment Details -> Edit Configuration -> Container

for more information check the documentation here: http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/customize-containers-ec2.html#customize-containers-format-options

Update

To prevent committing to your repository values like API keys, secrets and so on, you can put a placeholder value.

option_settings:
  - option_name: SOME_API_KEY
    value: placeholder-value-change-me

Later you can go to the AWS admin panel (Environment Details -> Edit Configuration -> Container) and update the values there. In my experience these values do not change after subsequent deployments.

Update 2 As @Benjamin stated in his comment, since the new look and feel was rolled out July 18, 2013 it is possible to define any number of environment variables directly from the console:

Configuration > Software Configuration > Environment Properties

As a heads up to anyone who uses the .ebextensions/*.config way: nowadays you can add, edit and remove environment variables in the Elastic Beanstalk web interface.

The variables are under Configuration → Software Configuration:

Creating the vars in .ebextensions like in Onema's answer still works.

It can even be preferable, e.g. if you will deploy to another environment later and are afraid of forgetting to manually set them, or if you are ok with committing the values to source control. I use a mix of both.