Elastic Beanstalk: add custom ELBv2 rules through configuration options

Question

Hi AWS community.

I manage an Elastic Beanstalk (EB) setup with Terraform. The setup contains an Application Load Balancer (LB). I selected a dedicated LB (LoadBalancerIsShared=false), so that EB creates and manages the LB.

I'm now required to add custom Listener rules, for example a fixed-response and a few redirects.

Unfortunately, I can't figure out how to add these through the configuration options and without manually using the Management Console. I can create a custom rule by applying the following options. For example:

```
Namespace: "aws:elbv2:listenerrule:foobar"
Name: "HostHeaders"
Value: "*.example.com"
```

```
Namespace: "aws:elbv2:listener:80"
Name: "Rules"
Value: "foobar"
```

How can I define an action such as "fixed-response" and the behavior of that action (HTML response code and text)? The [documentation](https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/command-options-general.html#command-options-general-elbv2-listenerrule) did not help.

I'd like to avoid the fallback option and create my own load balancer outside of EB. Although this sounds conceivable, I'd prefer to let EB take care of the LB if possible.

Thanks for any help.
Yarpen

Sean Nixon · Answer

There is no EB configuration option that allows you to specify fixed-response listener rules. What you can do instead is use EB's built-in functionality to add resource to the generated Cloudformation template to add a customer listener rule to your ALB with the desired fixed-response configuration. This is accomplished by creating a configuration file in the .ebextensions directory using the `Resources` key. You will need to find the CloudFormation resource name of the listener you wish to reference to add the rule. In the example below, it is `AWSEBV2LoadBalancerListener443`.

Example configuration file (.ebextensions/fixedResponse.config):

```yaml
Resources:
  fixedResponse404Listener:
    Type: AWS::ElasticLoadBalancingV2::ListenerRule
    Properties:
      Actions:
        - Type: fixed-response
          FixedResponseConfig:
            StatusCode: 200
            ContentType: "application/json"
            MessageBody: "{ \"hello\": \"world\"}"
      Conditions: 
        - Field: path-pattern
          PathPatternConfig:
            Values: 
              - "/my/fixed/response"
      ListenerArn: { "Ref" : "AWSEBV2LoadBalancerListener443" }
      Priority: 40000
```

Relevant documentation:
* https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/environment-resources.html
* https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/customize-containers-format-resources-eb.html

Elastic Beanstalk: add custom ELBv2 rules through configuration options

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