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Packer - What to do when there is no default VPC defined for the region?

#tools #devops

TL;DR

If the region you want to build a new AMI doesn't have a default VPC, you'll probably want a config like this:

# ...
source "amazon-ebs" "any_name" {
  # ...
  vpc_filter {
    filters = {
      "tag:Name"  = "vpc-name"
      "isDefault" = "false"
    }
  }
  subnet_filter {
    filters = {
      "state" = "available"
    }
    # if more than one subnet matches, pick one at random
    random = true
  }
}
# ...

explanation

I was tasked to create a custom Amazon Machine Image (AMI) and I decided to use Hashicorp Packer for that.

I quickly learned how to use Packer by following the official tutorials.

For creating an AMI, what Packer basically does is:

  1. reads the *.pkr.hcl file...
  2. create an AWS EC2 instance, starting from the AMI defined in the source block.
  3. run the instructions present in the build block.
  4. creates a snapshot and an AMI after build is done.
  5. destroys the EC2 instance.

The issue happened when I tried to use it in a real scenario where there was no default VPC defined in the region where I was wanting to create the AMI.

Fortunately you can specify a non-default VPC, like this:

# ...
source "amazon-ebs" "any_name" {
  # ...
  vpc_filter {
    filters = {
      "tag:Name"  = "vpc-name"
      "isDefault" = "false"
    }
  }
}

A new problem appear when your VPC has many available subnets, then Packer doesn't know which one to pick. Here's the solution

# ...
source "amazon-ebs" "any_name" {
  # ...
  subnet_filter {
    filters = {
      "state" = "available"
    }
    # if more than one subnet matches, pick one at random
    random = true
  }
}