How to mount secrets when building an image

[hector-sab]

I am trying to build an image so that I can test it, but it's failing with the error create container: build image: no active sessions. Any suggestion on how to fix this would be appreciated.

I think it has to do with buildkit (which I have enabled, see below) as whenever I remove --mount=type=secret,id=netrc,dst=/root/.netrc I can see logs form the build process when trying to run the snippet below.

RUN --mount=type=secret,id=netrc,dst=/root/.netrc \
    apk add --no-cache git \
    && go mod download -x -json

This is what I have so far.

package integration_test

import (
	"context"
	"testing"
	"time"

	"github.com/docker/docker/api/types/build"
	testcontainers "github.com/testcontainers/testcontainers-go"
)

const buildTimeout = 5 * time.Minute

func TestHelloWorld(t *testing.T) {
	ctx := context.Background()
	buildCtx, cancel := context.WithTimeout(ctx, buildTimeout)
	defer cancel()

	req := testcontainers.ContainerRequest{
		FromDockerfile: testcontainers.FromDockerfile{
			Context:    ".",
			Dockerfile: "Dockerfile",
			BuildOptionsModifier: func(buildOpt *build.ImageBuildOptions) {
				// Requires builtkit for mouting secrets
				// https://github.com/testcontainers/testcontainers-go/discussions/573
				buildOpt.Version = build.BuilderBuildKit
			},
		},
	}

	container, err := testcontainers.GenericContainer(buildCtx, testcontainers.GenericContainerRequest{
		ContainerRequest: req,
		Started:          true,
	})
	if err != nil {
		t.Fatalf("failed to start container: %v", err)
	}
}

This is the log when trying to do go test integration_test.go

=== RUN   TestHelloWorld
2025/12/12 15:07:40 github.com/testcontainers/testcontainers-go - Connected to docker:
  Server Version: 27.5.1
  API Version: 1.47
  Operating System: Ubuntu 24.04.3 LTS
  Total Memory: 15712 MB
  Testcontainers for Go Version: v0.40.0
  Resolved Docker Host: unix:///var/run/docker.sock
  Resolved Docker Socket Path: /var/run/docker.sock
  Test SessionID: 05cd1963cbf8e68c7b542dd906822c6a70a01bd22ef54515a7bd4020501dad3b
  Test ProcessID: e0fb70b9-3b1c-4206-a190-72d2724be9b2
2025/12/12 15:07:40 🐳 Building image 7f8225d0-3a3e-462e-ab0d-f3b736554d7f:b0682cd6-3013-4304-86c5-a16ee0079e71
    integration_test.go:43: failed to start container: create container: build image: no active sessions
--- FAIL: TestHelloWorld (1.04s)

[mdelapenya]

Hi @hector-sab there is no support for buildkit at the moment (#573), as there is no programmatic API for it. There could be something that shells out to bake directly, although I'd avoid that for not delivering a great UX for developers.