AWS Elastic Beanstalk: How to use environment variables in ebextensions? - amazon-web-services

Question

We are trying to store environment specific application configuration files in s3.
The files are stored in different subdirectories which are named after the environment and also have the environment as part of the file name.
Examples are
dev/application-dev.properties
stg/application-stg.properties
prd/application-prd.properties
The Elastic Beanstalk environments are named dev, stg, prd and alternatively I also have an environment variable defined in Elastic Beanstalk named ENVIRONMENT which can be dev, stg or prd.
My question now is, how do I reference the environment name or ENVIRONMENT variable when downloading the configuration file from a config file in .ebextensions?
I tried using a {"Ref": "AWSEBEnvironmentName" } reference in .ebextensions/myapp.config but get a syntax error when deploying.
The content of .ebextensions/myapp.config is:
files:
/config/application-`{"Ref": "AWSEBEnvironmentName" }`.properties:
mode: "000666"
owner: webapp
group: webapp
source: https://s3.amazonaws.com/com.mycompany.mybucket/`{"Ref": "AWSEBEnvironmentName" }`/application-`{"Ref": "AWSEBEnvironmentName" }`.properties
authentication: S3Access
Resources:
AWSEBAutoScalingGroup:
Metadata:
AWS::CloudFormation::Authentication:
S3Access:
type: S3
roleName: aws-elasticbeanstalk-ec2-role
buckets: com.mycompany.api.config
The error I get is:
The configuration file .ebextensions/myapp.config in application version
manualtest-18 contains invalid YAML or JSON. YAML exception: Invalid Yaml:
mapping values are not allowed here in "<reader>", line 6, column 85:
... .config/stg/application-`{"Ref": "AWSEBEnvironmentName" }`.prop ... ^ ,
JSON exception: Invalid JSON: Unexpected character (f) at position 0..
Update the configuration file.
What is the correct way of referencing an environment variable in a .ebextensions config file in AWS Elastic Beanstalk?

Answer 1

Your .ebextensions config file was almost correct. Substituting the file name with environment variable or AWS resource name won't work, for that do as in Mark's answer to rename the file created in container_commands section.
The source option value trying to access AWS resource name using Ref was correct, it just had to be surrounded by single quote ', like below:
files:
/config/application.properties:
mode: "000666"
owner: webapp
group: webapp
source: 'https://s3.amazonaws.com/com.mycompany.mybucket/`{"Ref": "AWSEBEnvironmentName" }`/application-`{"Ref": "AWSEBEnvironmentName" }`.properties'
authentication: S3Access
And to access environment variables use Fn::GetOptionSetting. Environment variables are in aws:elasticbeanstalk:application:environment namespace.
Below example access an environment variable ENVIRONMENT in source option of files:
files:
"/tmp/application.properties" :
mode: "000666"
owner: webapp
group: webapp
source: 'https://s3.amazonaws.com/com.mycompany.mybucket/`{"Ref": "AWSEBEnvironmentName" }`/application-`{"Fn::GetOptionSetting": {"Namespace": "aws:elasticbeanstalk:application:environment", "OptionName": "ENVIRONMENT ", "DefaultValue": "dev"}}`.properties'
authentication: S3Auth

Answer 2

I struggled to get this working, until I discovered that the Sub function doesn't appear to be available in ebextensions: http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/ebextensions-functions.html
This means that you need to fall back to Fn::Join and Ref, at least until support for Sub is introduced to ebextensions. It also seems that the files attribute requires a fixed path (and I couldn't use Fn::Join in this context).
My overall solution to this was as follows:
Resources:
AWSEBAutoScalingGroup:
Metadata:
AWS::CloudFormation::Authentication:
S3Auth:
type: S3
buckets: arn:aws:s3:::elasticbeanstalk-xxx
roleName: aws-elasticbeanstalk-ec2-role
files:
"/tmp/application.properties" :
mode: "000644"
owner: root
group: root
source: { "Fn::Join" : ["", ["https://s3-xxx.amazonaws.com/elasticbeanstalk-xxx/path/to/application-", { "Ref" : "AWSEBEnvironmentName" }, ".properties" ]]}
authentication: S3Auth
container_commands:
01-apply-configuration:
command: mkdir -p config && mv /tmp/application.properties config
This will result in an application.properties file (without the environment name qualifier) in a config directory next to the deployed application instance.
If you want to keep the name of the environment as part of the file name using this approach, you will need to adjust the command that moves the file to use another Fn::Join expression to control the filename.

Answer 3

You are almost there .ebextensions are using YAML format, while your trying to use JSON. Use Ref: AWSEBEnvironmentName.
In addition, you can take advantage of Sub function to avoid pesky Join:
!Sub "/config/application-${AWSEBEnvironmentName}.properties"