Customizing Windows Elastic Beanstalk Environments – Part 2

In the previous post in this series, we introduced the .ebextensions/*config file, and showed how you can use it to install packages, download files, run commands, and start services.

In this post, we’re going to dig a little bit into managing settings through this mechanism.

Writing configuration files

A common way to configure software systems is through text-based configuration. Elastic Beanstalk gives a couple of ways for us to write files in the filesystem that are not necessarily part of our web application, and which may live outside the web application directory. Files can be downloaded from a web-accessible place (such as an S3 bucket) or inlined in the .ebextensions/*.config file directly.

files:
   c:/MyApplicationSupport/main.conf:
     content: |
       <configuration>
         <environment>production</environment>
         <maxConnections>500</maxConnection>
         <defaultUser>guest</defultUser>
       <configuration>
   c:/MyApplicationSupport/auxilliary.conf:
     source: http://my-application-support/auxilliary.conf

The first file in the files: array shows an example of inlining.

Inlining can be handy for situations where you are adjusting content frequently—for example, during development when you are deploying your application more often. Using the source: key requires uploading any changes before deployment, so that’s a better method for more complex, or less volatile files.

Variable interpolation

Another benefit to inlining is that you can use the AWS CloudFormation intrinsic functions to interpolate information from the CloudFormation template associated with your Elastic Beanstalk environment into your configuration files.

Here are some examples of interpolation:

files:
   c:/cfn/environmentInfo.txt:
     content : |
       Environment Name: `{"Ref": "AWSEBEnvironmentName" }`
       Environment Id:   `{"Ref": "AWSEBEnvironmentId" }`
       Instance Type:    `{"Ref": "InstanceType" }`
       Stack Id:         `{"Ref": "AWS::StackId" }`
       Region:           `{"Ref": "AWS::Region" }`
       AMI Id:           `{"Fn::FindInMap": [ "AWSEBAWSRegionArch2AMI", { "Ref": "AWS::Region" }, { "Fn::FindInMap": [ "AWSEBAWSInstanceType2Arch", { "Ref": "InstanceType" }, "Arch" ]}]}`