docker buildx bake and variables

[elangelo]

I have a Dockerfile that defines multiple targets that i can build.

so I created a docker-bake.hcl:

variable "IMAGES" { 
  default = [ "foo", "bar" ]
}
variable "TAG" {
  default = "dev"
}
target "dev-env" {
  name = ${tgt}
  tags = "${tgt}:${TAG}"
  context = "."
  dockerfile = "Dockerfile"
  matrix = {
    tgt = IMAGES
  }
}

imagine the Dockerfile looks something like this:

FROM python:3.11-slim-bookworm AS base

FROM base AS foo
FROM base AS bar
FROM base AS dev

This works like a charm.

Though I'm struggling to override the IMAGES from the commandline
Imagine I also want to build the dev target

IMAGES="[foo,bar,dev]" docker buildx bake dev-env

results in:

docker-bake.hcl:1
--------------------
   1 | >>> variable "IMAGES" { 
   2 |       default = [ "foo", "bar" ]
   3 |     }
--------------------
ERROR: docker-bake.hcl:1,19-19: Invalid value; unsupported type tuple for variable IMAGES

[elangelo]

I've actually noticed that the whole handling of the IMAGES variable is going wrong. If you add a another target that uses that IMAGES as a matrix e.g.:

target "prod-env" {
  name = ${tgt}
  tags = "${tgt}:prod"
  context = "."
  dockerfile = "Dockerfile"
  matrix = {
    tgt = IMAGES
  }
}

when you now try to build the dev-env it always build the prod-env.
so docker buildx bake dev-env --print actually clearly shows that it's going to build the prod environment (you can see in the tags which i hardcoded to prod in prod-env

[elangelo]

Did some further fiddling and I found a solution.
First of all the second was not really a problem, you need to make sure the 'name' is unique (not only in your target but in your whole hcl file) so i just appended an identifier:
name = "{tgt}-prod-env"
and that worked like a charm.

Passing in the IMAGES as an array did not work. Somehow coercing an environment variable to an array never worked, so I took another approach where i pass in the IMAGES as a string and then parse them in the hcl itself:

variable "IMAGES" {
  default = "foo bar"
}
variable "TAG" {
  default = "dev"
}
target "dev-env" {
  name = "${tgt}-dev-env"
  tags = [ "${tgt}:${TAG}" ]
  context = "."
  dockerfile = "Dockerfile"
  matrix = {
    tgt = split(" ", IMAGES)
  }
}
target "prod-env" {
  name = "${tgt}-prod-env"
  tags = [ "${tgt}:prod" ]
  context = "."
  dockerfile = "Dockerfile"
  matrix = {
    tgt = split(" ", IMAGES)
  }
}

results in:

❯ IMAGES="foo bar show" docker buildx bake dev-env --print
[+] Building 0.0s (1/1) FINISHED                                                                                                                                                      
 => [internal] load local bake definitions                                                                                                                                       0.0s
 => => reading docker-bake.hcl 978B / 978B                                                                                                                                       0.0s
{
  "group": {
    "default": {
      "targets": [
        "dev-env"
      ]
    },
    "dev-env": {
      "targets": [
        "foo-dev-env",
        "bar-dev-env",
        "show-dev-env"
      ]
    }
  },
  "target": {
    "bar-dev-env": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "tags": [
        "bar:dev"
      ]
    },
    "foo-dev-env": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "tags": [
        "foo:dev"
      ]
    },
    "show-dev-env": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "tags": [
        "show:dev"
      ]
    }
  }
}