Terraform: Define AWS Security Group for All ICMP Traffic

Define AWS Security Group for All ICMP Traffic in Terraform

It is not quite well documented in Terraform what "from" and "to" port number that need to define to allow All ICMP traffic. If you're having hard time trying to figure out here is the solution to All ICMP traffic in Security Group.

...
ingress {
  ...
  from_port   = -1
  to_port     = -1
  protocol    = "icmp"
  ...
}
...

That's it. The special number "-1" did the trick.

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Terraform: Force Destroy Resource when prevent_destroy is true

How to Force Destroy Resource in Terraform

Terraform resource that having lifecycle prevent_destroy = true can not be destroyed. You need to manually edit the file inplace and change the value prevent_destroy to false manually each time you want to destroy the resource. Instead of having to edit manually and make git status dirty we can automate this using simple shell script.

Automate Force Destroy Resource in Terraform

The idea is simple.

1. Search all *.tf files and look the value of prevent_default = true to prevent_default = false
2. Run terraform destroy command
3. Revert the changes back to prevent_default = true

Here is the implementation in Bash.

#!/bin/bash

$ find . -name '*.tf' -type f \
-exec perl -i -pe 's@prevent_destroy = true@prevent_destroy = false@g' {} \;

# Run terraform destroy
[ "$IS_PLAN" = "yes" ] && terraform plan -destroy || terraform destroy $@

# Revert the changes
$ find . -name '*.tf' -type f \
 -exec perl -i -pe 's@prevent_destroy = false@prevent_destroy = true@g' {} \;

Save the file with name e.g: terraform-force-destroy.sh. To issue terraform plan -destroy command use the following.

$ IS_PLAN=yes bash terraform-force-destroy.sh

To force destroy the resource use the following command.

$ bash terraform-force-destroy.sh -auto-approve

You can give normal terraform's arguments just like the original terraform destroy.

References for Terraform Force Destroy

• https://github.com/hashicorp/terraform/issues/3640
• https://stackoverflow.com/questions/38354725/prevent-sed-from-adding-newlines-at-the-end-of-files
• https://spacelift.io/blog/how-to-destroy-terraform-resources

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