How to prevent Rails 6 from blocking my AWS EC2 instances?

Question

I have some Rails 6 applications, deployed at AWS, via Opsworks.

After upgrading to Rails 6 the app blocks the health check of its own instance and it causes the load balancer to take the instance down.

I would like to know how to whitelist all my EC2 instances automatically with dynamic IP addresses? Instead of adding one by one to config/application.rb?

Thanks

Rails.application.configure do
  # Whitelist one hostname
  config.hosts << "hostname"
  # Whitelist a test domain
  config.hosts << /application\.local\Z/
  # config.hosts.clear 
end

Countercheck

Answer 1

The work-around that worked for me was

config.hosts.clear

Hatch

Thank you, It looks like this is the current workaround for mee too, but it is not ideal since it disables the feature. Best – Countercheck

I do not think this is really safe as in this way, you will allow all hosts access to your application. You should rather whitelist the hosts you want. – Selfrealization

Answer 2

I posted this question a while back. A safer solution would be reading the IP addresses from environmental variables that can be set from the AWS console.

config.hosts << ENV["INSTANCE_IP"]
config.hosts << ENV["INSTANCE_IP2"]
...
config.hosts << ENV["INSTANCE_IPn"]

At least in this way it does not require a new git commit every time the IP address changes when the instance has a dynamic IP.

Countercheck

Answer 3

remove any config.hosts << "hostname" from application.rb config - then rails won't block hosts

Sheeting

Answer 4

Simple solution is to allow the Health Checker user agent, add this to your production.log

  config.host_authorization = {
    exclude: ->(request) { request.user_agent =~ /ELB-HealthChecker/ }
  }

Prop

Answer 5

Looks like it has been resolved in the latest versions atleast works on 6.1 and above

https://guides.rubyonrails.org/configuring.html#actiondispatch-hostauthorization

You can exclude certain requests from Host Authorization checks by setting config.host_configuration.exclude:

# Exclude requests for the /healthcheck/ path from host checking
Rails.application.config.host_configuration = {
  exclude: ->(request) { request.path =~ /healthcheck/ }
}

Belittle

Note this is incorrect. Rails.application.config.host_configuration does not exist. it should be Rails.application.config.host_authorization – Prop