{{timestamp}} doesn't remain constant in post processor manifest

[pkeecom]

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Overview of the Issue

We have a locals to create tags on the AMI which in turn is used to write to manifest.

locals {
  tstamp = "{{timestamp}}"
  tags = {
    Name = "${var.ami_prefix}-${local.tstamp}"
   ....
  }

These tags are applied fine on the AMI.

We also have a post processor section.

post-processors {
  post-processor "manifest" {
   ...
  custom_data = {
    ....
    ami_name = local.tags.Name
  }
  }
}

The ami_name in manifest file should be the same as AMI name of the AMI. But, on certain occasions, it is a few seconds out i.e. it does not match the actual AMI Name. The problem is very random.

Reproduction Steps

The problem is very random. It is not reproducible every time.

Packer version

Any including latest

Operating system and Environment details

Redhat Linux 9.6

Logs

$ packer build -machine-readable packer/images-ebs/ | tee packer.out
1761565722,,ui,say,==> amazon-ebs.base: Prevalidating any provided VPC information
1761565722,,ui,say,==> amazon-ebs.base: Prevalidating AMI Name:MYAMI-v9.6-v26.4.2-1761565720
1761565722,,ui,say,==> amazon-ebs.base: Found Image ID: __hidden__
1761565722,,ui,say,==> amazon-ebs.base: Found VPC ID: __hidden__
1761565722,,ui,say,==> amazon-ebs.base: Found Subnet ID: __hidden__
1761565722,,ui,say,==> amazon-ebs.base: Creating temporary keypair: __hidden__
1761565723,,ui,say,==> amazon-ebs.base: Found Security Group(s): __hidden__
1761565723,,ui,say,==> amazon-ebs.base: Launching a source AWS instance...
1761565723,,ui,say,==> amazon-ebs.base: Adding tag: "Base_AMI_Name": "__hidden__"
1761565723,,ui,say,==> amazon-ebs.base: Adding tag: "Component": "packer"
1761565723,,ui,say,==> amazon-ebs.base: Adding tag: "Name": "MYAMI-v9.6-v26.4.2-1761565720"
...
...
1761565723,,ui,say,==> amazon-ebs.base: Adding tag: "Name": "MYAMI-v9.6-v26.4.2-1761565720"
...
1761565742,,ui,say,==> amazon-ebs.base: Using SSH communicator to connect: 10.195.13.37
1761565742,,ui,say,==> amazon-ebs.base: Waiting for SSH to become available...
1761565775,,ui,say,==> amazon-ebs.base: Connected to SSH!
...
...snip to end..
...
1761566241,,ui,say,==> amazon-ebs.base: Adding tag: "Name": "MYAMI-v9.6-v26.4.2-1761565720"
1761566259,,ui,say,==> amazon-ebs.base: Running post-processor:  (type manifest)
1761566259,,ui,say,Build 'amazon-ebs.base' finished after 8 minutes 58 seconds.
1761566259,amazon-ebs.base,artifact,1,end
1761566259,,ui,say,--> amazon-ebs.base: AMIs were created:\neu-west-2: ami-__hidden_\n

Contents of manifest.json

{
  "builds": [
    {
      "name": "base",
      "builder_type": "amazon-ebs",
      "build_time": 1761566259,
      "files": null,
      "artifact_id": "eu-west-2:ami-__hidden__",
      "packer_run_uuid": "27ef8979-e7eb-088d-31eb-cc3d9cc974e9",
      "custom_data": {
        "ami_name": "MYAMI-v9.6-v26.4.2-1761565721",
        "ami_source_id": "ami-__hidden__",
        "ami_source_name": "__hidden__",
        "ami_version": "v26.4.2",
        "baseline": "__hidden__",
        "instance_id": "__hidden__",
        "os_major_version": "9",
        "os_version": "9.6"
      }
    }
  ],
  "last_run_uuid": "27ef8979-e7eb-088d-31eb-cc3d9cc974e9"
}

In the above logs, you can see that timestamp has shifted by 1.
Actual AMI Name: MYAMI-v9.6-v26.4.2-1761565720
AMI Name recorded in manifest: MYAMI-v9.6-v26.4.2-1761565721

Note: We use {{timestamp}} because there's no built in method to get time since epoch.