Cannot export image config with environment variables

[csweichel]

I'm trying to build an image using LLB directly, and fail to make it export the image config as well. Naturally this results in missing environment variables, and other bits of configuration. During the build the config is as expected - the env var is present.
This issue persists if I write the LLB to stdout and pipe it to buildctl build --output .... I reckon I'm misunderstanding how to use LLB.

Is there some bit of documentation that I'm missing?

The following code reproduces the issues:

package main

import (
	"context"
	"flag"
	"log"
	"os"

	"github.com/containerd/console"
	"github.com/moby/buildkit/client"
	"github.com/moby/buildkit/client/llb"
	"github.com/moby/buildkit/client/llb/imagemetaresolver"
	"github.com/moby/buildkit/util/progress/progressui"
	"golang.org/x/sync/errgroup"
)

var dest = flag.String("dest", "", "destination ref to push to")

func main() {
	flag.Parse()
	if *dest == "" {
		log.Fatal("missing --dest")
	}

	ctx := context.Background()
	state := llb.Image("docker.io/library/alpine:latest", llb.WithMetaResolver(imagemetaresolver.Default())).
		AddEnv("this-env-var", "is-not-exported").
		Dir("/some-directory").
		Run(llb.Shlex("env")).
		Root()

	def, err := state.Marshal(ctx, llb.LinuxAmd64)
	if err != nil {
		log.Fatal(err)
	}

	solveOpt := client.SolveOpt{
		Exports: []client.ExportEntry{
			{
				Type: "image",
				Attrs: map[string]string{
					"name": *dest,
					"push": "true",
				},
			},
		},
	}

	cl, err := client.New(ctx, "unix:///run/buildkit/buildkitd.sock", client.WithFailFast())
	if err != nil {
		log.Fatal(err)
	}
	eg, ctx := errgroup.WithContext(ctx)
	ch := make(chan *client.SolveStatus)
	eg.Go(func() error {
		_, err := cl.Solve(ctx, def, solveOpt, ch)
		if err != nil {
			return err
		}
		return nil
	})
	eg.Go(func() error {
		var c console.Console
		return progressui.DisplaySolveStatus(ctx, "", c, os.Stdout, ch)
	})
	err = eg.Wait()
	if err != nil {
		log.Fatal(err)
	}
}

[tonistiigi]

See https://stackoverflow.com/questions/58508711/using-docker-buildkits-go-client-how-do-i-add-an-entrypoint/58547317#58547317

[csweichel]

Thank you very much for the pointer, that was very helpful indeed :)