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+---
+author: "parsec"
+date: 2023-02-16
+linktitle: Packer Variable Files, and How to Write Them
+type:
+  - post
+  - posts
+title: Packer Variable Files, and How to Write Them
+subtitle: A Missing Docs Mystery
+weight: 10
+series:
+  - "Missing Docs"
+tags:
+  - packer
+  - gitops
+---
+
+---
+
+## Backstory
+
+So, I had to create some AMIs.
+
+"Sure, no big deal", I thought, "I'll use Packer!"
+
+The Packer templates themselves aren't too bad. It kind of sucks to parse through Hashicorp's documentation, but sometimes I just need some really explicit instructions. So I write my templates, they work after some debugging, life is good.
+
+New problem: I need to set passwords for various accounts on these AMIs. Time to use some variables!
+
+Except... [the Hashicorp documentation](https://developer.hashicorp.com/packer/docs/templates/hcl_templates/variables#assigning-values-to-input-variables) on variables is... a little lacking, to be honest. It explains under the **Standard Variable Definitions Files** heading that the format should look like such:
+
+```hcl
+image_id = "ami-abc123"
+availability_zone_names = [
+  "us-east-1a",
+  "us-west-1c",
+]
+```
+
+Easy enough, right? It's just some variables being set in a separate file, then you bring it in with a command like so:
+
+```hcl
+$ packer build -var-file="testing.pkrvars.hcl"
+
+Error: Failed preparing provisioner-block "shell" ""
+
+  on jenkins.pkr.hcl line 44:
+  (source code not available)
+
+jenkins.pkr.hcl:46,27-40: Unsupported attribute; This object does not have an
+attribute named "jenkins_pass"., and 3 other diagnostic(s)
+```
+
+So... that error points us to the **Important do not skip** block in the docs:
+
+> Important: Unlike legacy JSON templates the input variables within a variable definitions file must be declared via a variables block within a standard HCL2 template file *.pkr.hcl before it can be assigned a value. Failure to do so will result in an unknown variable error during Packer's runtime.
+
+Okay, sure... I was a little confused here, to be honest. It sounded like I should be changing the name of the variable file to something like `vars.pkr.hcl`, but that didn't work. Then it just asked me to set up `variables` blocks. And putting everything in the variable definition files in a `variables` block didn't work, so what gives?
+
+## The Solution
+
+Now that I read back on it, it makes sense. It did not when I was looking at it. So, dear reader, I hope this will help!
+
+### Defining Your Variables
+
+So now we have some variable definitions; how do we get those values into our Packer templates?
+
+`vars.pkr.hcl` - it can technically be named anything, but this name means I don't get it confused with other stuff.
+
+```hcl
+variable "web_pass" {
+  type      = string
+  default   = ""
+  sensitive = true
+}
+
+variable "user_pass" {
+  type      = string
+  default   = ""
+  sensitive = true
+}
+```
+
+Notice that we left the `default` value set to `nil`. Also, since my use case was for passwords, I set the `sensitive` flag. This means when the variable is consumed, it won't be printed in the console or log.
+
+### The Variable Definition File
+
+This file should be named something with the extension `.pkrvars.hcl`. If you want it to be really fancy, as long as you're only using one `pkrvars` file you can do `.auto.pkrvars.hcl`, and Packer will automagically pick up the variables file.
+
+Your file should look something like this:
+
+```hcl
+var1        = "hello"
+var2        = 12345
+var3        = ["a","b","c"]
+...
+```
+
+Now, this file's purpose is to assign values to existing variables, hence the warning they gave us. So, to make this work for us, we *also* need to define the variables in some kind of `.pkr.hcl` file. For me, this was just a `vars.pkr.hcl` file, like we discussed above.
+
+So, we have two pieces of the puzzle now. Variable declarations, and variable definitions. These definitions will overwrite the default value of our declared variables. But how do we consume them?
+
+### Consuming Variables in Packer Templates
+
+To call a variable in packer, you encapsulate it in `${var.x}`. Not too bad, right?
+
+Example:
+
+```hcl
+... ${var.var1}
+... ${var.var2}
+... ${var.var3}
+```
+
+This part is actually way easier than it sounds, especially if you used [Auto-loaded Variable Definitions Files](https://developer.hashicorp.com/packer/docs/templates/hcl_templates/variables#auto-loaded-variable-definitions-files). If you did, when you run `packer build .` it should Just Work.
+
+If not, you'll want to specific your variables file like so:
+
+```shell
+$ packer build -var-file=./vars.pkrvars.hcl
+
+[build_output_here]
+```
+
+## In Closing
+
+And now, assuming nothing weird happened, you should have a Packer template consuming custom variables at runtime! The beautiful thing about doing vairables this way instead of `locals` is that they can be overwritten at runtime. So, for example:
+
+```hcl
+packer build -var="key":"value" .
+```
+
+This would overwrite whatever variable name you give it (or create a new one if it doesn't exist, at runtime).
+
+Pretty nifty, right? I think so. But I'll probably be writing a few more of these in the future... These docs could use some help, and if I'm using the tools anyway, I might as well help other people use them :)