Packer: git-hash function for naming of the resulting file

[brettswift]

I currently customize my post_processor like this:

"output": "boxes/rhel-server-6.5-x64-{{.Provider}}-{{.BuildName}}_{{timestamp}}.box"

It would be nice to have {{git_hash}} instead of timestamp. If there's another way of doing this, other than a function call in packer, then I guess I'm not familiar enough on how to do it.

I see where this might be done: packer/config_template.go.

I thought most people would find this useful.

Ex: If we want to know the entire configuration of our puppet stack, we should also know which packer box each node was built on, and timestamp doesn't give us that. It's a good thing to have for auditing or even the nastiest of nasty disaster recovery strategies.

Thoughts? Alternatives?

_edit_:

There's also the use case of running packer against a dirty git tree, where the resulting hash wouldn't be accurate. You'd probably want the git hash to return 'dirty_tree' in that case..

[sethvargo]

Hm. I think adding git-specific functions is tricky, because it opens the door for other SCMs which we may not have the same level of expertise on. Is there a reason you can't use a user-var for this like:

packer -var "git_sha=`git rev-parse HEAD`"

And then declare the variable:

{
  "variables": {
    "git_sha": "none"
  }
}

{{git_hash}} makes a few assumptions, the most important being - you have Git installed. I do not think all our users use Git, so finding the correct UX when git is not installed might be difficult (do we error, replace with an empty string, etc).

[mitchellh]

Agreed with @sethvargo

[joelittlejohn]

Another tiny tip for people that are reading this: you might want to use the --short argument for rev-parse:

packer -var "git_sha=`git rev-parse --short HEAD`"

to get a value like 21feafa instead of 21feafa9a86a45b3008d133f0803d2ac2087c63f.