This follows #8232 which added the code to generate the code required to parse
HCL files for each packer component.
All old config files of packer will keep on working the same. Packer takes one
argument. When a directory is passed, all files in the folder with a name
ending with “.pkr.hcl” or “.pkr.json” will be parsed using the HCL2 format.
When a file ending with “.pkr.hcl” or “.pkr.json” is passed it will be parsed
using the HCL2 format. For every other case; the old packer style will be used.
## 1. the hcl2template pkg can create a packer.Build from a set of HCL (v2) files
I had to make the packer.coreBuild (which is our one and only packer.Build ) a public struct with public fields
## 2. Components interfaces get a new ConfigSpec Method to read a file from an HCL file.
This is a breaking change for packer plugins.
a packer component can be a: builder/provisioner/post-processor
each component interface now gets a `ConfigSpec() hcldec.ObjectSpec`
which allows packer to tell what is the layout of the hcl2 config meant
to configure that specific component.
This ObjectSpec is sent through the wire (RPC) and a cty.Value is now
sent through the already existing configuration entrypoints:
Provisioner.Prepare(raws ...interface{}) error
Builder.Prepare(raws ...interface{}) ([]string, error)
PostProcessor.Configure(raws ...interface{}) error
close#1768
Example hcl files:
```hcl
// file amazon-ebs-kms-key/run.pkr.hcl
build {
sources = [
"source.amazon-ebs.first",
]
provisioner "shell" {
inline = [
"sleep 5"
]
}
post-processor "shell-local" {
inline = [
"sleep 5"
]
}
}
// amazon-ebs-kms-key/source.pkr.hcl
source "amazon-ebs" "first" {
ami_name = "hcl2-test"
region = "us-east-1"
instance_type = "t2.micro"
kms_key_id = "c729958f-c6ba-44cd-ab39-35ab68ce0a6c"
encrypt_boot = true
source_ami_filter {
filters {
virtualization-type = "hvm"
name = "amzn-ami-hvm-????.??.?.????????-x86_64-gp2"
root-device-type = "ebs"
}
most_recent = true
owners = ["amazon"]
}
launch_block_device_mappings {
device_name = "/dev/xvda"
volume_size = 20
volume_type = "gp2"
delete_on_termination = "true"
}
launch_block_device_mappings {
device_name = "/dev/xvdf"
volume_size = 500
volume_type = "gp2"
delete_on_termination = true
encrypted = true
}
ami_regions = ["eu-central-1"]
run_tags {
Name = "packer-solr-something"
stack-name = "DevOps Tools"
}
communicator = "ssh"
ssh_pty = true
ssh_username = "ec2-user"
associate_public_ip_address = true
}
```
It is simply the best/simplest solution and trying to prevent users from passing and integer here would be like opening a can of worms. Because:
* we cannot make mapstructure validate our duration string ( with an UnmarshalJSON func etc.)
* we cannot make mapstructure spit a string instead of a duration and packer will decode-encode-decode config.
* the hcl2 generated code asks for a string, so this will be enforced by default.
Before this commit it was possible to set a duration using an integer or a float. Go's time.Duration is an int64 internally an mapstructure will take advantage of this and load the number as a int64 but `1` means one ns which is unexpected/confusing. To avoid confusion and enforce readability this forces users to pass a string with a unit for a duration; ex "56s".
mapstructure-to-hcl2 fills the gaps between hcl2 and mapstructure for Packer
By generating a struct that the HCL2 ecosystem understands making use of
mapstructure tags.
Packer heavily uses the mapstructure decoding library to load/parse user
config files. Packer now needs to move to HCL2.
Here are a few differences/gaps betweens hcl2 and mapstructure:
* in HCL2 all basic struct fields (string/int/struct) that are not pointers
are required ( must be set ). In mapstructure everything is optional.
* mapstructure allows to 'squash' fields
(ex: Field CommonStructType `mapstructure:",squash"`) this allows to
decorate structs and reuse configuration code. HCL2 parsing libs don't have
anything similar.
mapstructure-to-hcl2 will parse Packer's config files and generate the HCL2
compliant code that will allow to not change any of the current builders in
order to move to HCL2 to softly move to HCL2.
Adrien Delorme
Adrien Delorme
Megan Marsh