i am trying my hands on packer.

i was able to create an image for ubuntu 16.04 by 

```
"source_ami_filter": {
          "filters": {
            "virtualization-type": "hvm",
            "name": "ubuntu/images/*ubuntu-xenial-16.04-amd64-server-*",
            "root-device-type": "ebs"
          },

```

but when it try the same filer by modifying 16.04 to 18.04 

```
"source_ami_filter": {
          "filters": {
            "virtualization-type": "hvm",
            "name": "ubuntu/images/*ubuntu-xenial-18.04-amd64-server-*",
            "root-device-type": "ebs"
          },

```

i get the below error .

```
==> amazon-ebs: Prevalidating any provided VPC information
==> amazon-ebs: Prevalidating AMI Name: packer-example 1592389575
==> amazon-ebs: No AMI was found matching filters: {
==> amazon-ebs:   Filters: [{
==> amazon-ebs:       Name: "virtualization-type",
==> amazon-ebs:       Values: ["hvm"]
==> amazon-ebs:     },{
==> amazon-ebs:       Name: "name",
==> amazon-ebs:       Values: ["ubuntu/images/*ubuntu-xenial-18.04-amd64-server-*"]
==> amazon-ebs:     },{
==> amazon-ebs:       Name: "root-device-type",
==> amazon-ebs:       Values: ["ebs"]
==> amazon-ebs:     }],
==> amazon-ebs:   Owners: ["099720109477"]
==> amazon-ebs: }
Build 'amazon-ebs' errored: No AMI was found matching filters: {
  Filters: [{
      Name: "virtualization-type",
      Values: ["hvm"]
    },{
      Name: "name",
      Values: ["ubuntu/images/*ubuntu-xenial-18.04-amd64-server-*"]
    },{
      Name: "root-device-type",
      Values: ["ebs"]
    }],
  Owners: ["099720109477"]
}

==> Some builds didn't complete successfully and had errors:
--> amazon-ebs: No AMI was found matching filters: {
  Filters: [{
      Name: "virtualization-type",
      Values: ["hvm"]
    },{
      Name: "name",
      Values: ["ubuntu/images/*ubuntu-xenial-18.04-amd64-server-*"]
    },{
      Name: "root-device-type",
      Values: ["ebs"]
    }],
  Owners: ["099720109477"]
}

```

Wanted to how filter values work :

1. for 18.04 ?
2. for another other image(linux/redhat) ?

Could some one please clear the doubt i have with regards to this ?