aws.centos7.pkr.hcl

packer {
  required_plugins {
    amazon = {
      version = ">= 0.0.2"
      source  = "github.com/hashicorp/amazon"
    }
  }
}

source "amazon-ebs" "centos7" {
  ami_name      = "packer-centos7-aws"
  instance_type = "t2.micro"
  region        = "ap-southeast-1"

  associate_public_ip_address = true
  source_ami_filter {
    filters = {
      name = "your-company-base-centos7-image*"
      architecture = "x86_64"
      root-device-type = "ebs"
      virtualization-type = "hvm"
    }
    most_recent = true
    owners      = ["XXXXXXXX"]
  }
  ssh_username = "centos"
}

build {
  name = "packer-centos7-aws"
  sources = [
    "source.amazon-ebs.centos7"
  ]

  provisioner "shell" {
    environment_vars = [
      "https_proxy=http://yourproxyserver:port",
    ]
    inline = [
      "echo update yum",
      "sudo yum update -y",
      "echo Installing JDK",
      "sudo yum install -y java-11-openjdk-devel",
    ]
  }
}

aws.centos7.snippet1.pkr.hcl

    inline = [
      "sudo echo proxy='http://yourproxyserver:port' >> /etc/yum.conf",
      # and the rest
    ]

aws.centos7.snippet2.pkr.hcl

    inline = [
      "sudo bash -c \"echo proxy='http://yourproxyserver:port' >> /etc/yum.conf\"",
      # and the rest
    ]