fix: Allow terraform provisions to be gracefully cancelled (#3526)

* fix: Allow terraform provisions to be gracefully cancelled

This change allows terraform commands to be gracefully cancelled on
Unix-like platforms by signaling interrupt on provision cancellation.

One implementation detail to note is that we do not necessarily kill a
running terraform command immediately even if the stream is closed. The
reason for this is to allow for graceful cancellation even in such an
event. Currently the timeout is set to 5 minutes by default.

Related: #2683

The above issue may be partially or fully fixed by this change.

* fix: Remove incorrect minimumTerraformVersion variable

* Allow init to return provision complete response

provisioner/terraform/executor.go

@@ -41,7 +41,7 @@ func (e executor) basicEnv() []string {
 	return env
 }
 
-func (e executor) execWriteOutput(ctx context.Context, args, env []string, stdOutWriter, stdErrWriter io.WriteCloser) (err error) {
+func (e executor) execWriteOutput(ctx, killCtx context.Context, args, env []string, stdOutWriter, stdErrWriter io.WriteCloser) (err error) {
 	defer func() {
 		closeErr := stdOutWriter.Close()
 		if err == nil && closeErr != nil {
@@ -52,8 +52,12 @@ func (e executor) execWriteOutput(ctx context.Context, args, env []string, stdOu
 			err = closeErr
 		}
 	}()
+	if ctx.Err() != nil {
+		return ctx.Err()
+	}
+
 	// #nosec
-	cmd := exec.CommandContext(ctx, e.binaryPath, args...)
+	cmd := exec.CommandContext(killCtx, e.binaryPath, args...)
 	cmd.Dir = e.workdir
 	cmd.Env = env
 
@@ -63,19 +67,36 @@ func (e executor) execWriteOutput(ctx context.Context, args, env []string, stdOu
 	cmd.Stdout = syncWriter{mut, stdOutWriter}
 	cmd.Stderr = syncWriter{mut, stdErrWriter}
 
-	return cmd.Run()
+	err = cmd.Start()
+	if err != nil {
+		return err
+	}
+	interruptCommandOnCancel(ctx, killCtx, cmd)
+
+	return cmd.Wait()
 }
 
-func (e executor) execParseJSON(ctx context.Context, args, env []string, v interface{}) error {
+func (e executor) execParseJSON(ctx, killCtx context.Context, args, env []string, v interface{}) error {
+	if ctx.Err() != nil {
+		return ctx.Err()
+	}
+
 	// #nosec
-	cmd := exec.CommandContext(ctx, e.binaryPath, args...)
+	cmd := exec.CommandContext(killCtx, e.binaryPath, args...)
 	cmd.Dir = e.workdir
 	cmd.Env = env
 	out := &bytes.Buffer{}
 	stdErr := &bytes.Buffer{}
 	cmd.Stdout = out
 	cmd.Stderr = stdErr
-	err := cmd.Run()
+
+	err := cmd.Start()
+	if err != nil {
+		return err
+	}
+	interruptCommandOnCancel(ctx, killCtx, cmd)
+
+	err = cmd.Wait()
 	if err != nil {
 		errString, _ := io.ReadAll(stdErr)
 		return xerrors.Errorf("%s: %w", errString, err)
@@ -95,11 +116,11 @@ func (e executor) checkMinVersion(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	if !v.GreaterThanOrEqual(minimumTerraformVersion) {
+	if !v.GreaterThanOrEqual(minTerraformVersion) {
 		return xerrors.Errorf(
 			"terraform version %q is too old. required >= %q",
 			v.String(),
-			minimumTerraformVersion.String())
+			minTerraformVersion.String())
 	}
 	return nil
 }
@@ -109,6 +130,10 @@ func (e executor) version(ctx context.Context) (*version.Version, error) {
 }
 
 func versionFromBinaryPath(ctx context.Context, binaryPath string) (*version.Version, error) {
+	if ctx.Err() != nil {
+		return nil, ctx.Err()
+	}
+
 	// #nosec
 	cmd := exec.CommandContext(ctx, binaryPath, "version", "-json")
 	out, err := cmd.Output()
@@ -130,7 +155,7 @@ func versionFromBinaryPath(ctx context.Context, binaryPath string) (*version.Ver
 	return version.NewVersion(vj.Version)
 }
 
-func (e executor) init(ctx context.Context, logr logger) error {
+func (e executor) init(ctx, killCtx context.Context, logr logger) error {
 	outWriter, doneOut := logWriter(logr, proto.LogLevel_DEBUG)
 	errWriter, doneErr := logWriter(logr, proto.LogLevel_ERROR)
 	defer func() {
@@ -156,11 +181,11 @@ func (e executor) init(ctx context.Context, logr logger) error {
 		defer e.initMu.Unlock()
 	}
 
-	return e.execWriteOutput(ctx, args, e.basicEnv(), outWriter, errWriter)
+	return e.execWriteOutput(ctx, killCtx, args, e.basicEnv(), outWriter, errWriter)
 }
 
 // revive:disable-next-line:flag-parameter
-func (e executor) plan(ctx context.Context, env, vars []string, logr logger, destroy bool) (*proto.Provision_Response, error) {
+func (e executor) plan(ctx, killCtx context.Context, env, vars []string, logr logger, destroy bool) (*proto.Provision_Response, error) {
 	planfilePath := filepath.Join(e.workdir, "terraform.tfplan")
 	args := []string{
 		"plan",
@@ -184,11 +209,11 @@ func (e executor) plan(ctx context.Context, env, vars []string, logr logger, des
 		<-doneErr
 	}()
 
-	err := e.execWriteOutput(ctx, args, env, outWriter, errWriter)
+	err := e.execWriteOutput(ctx, killCtx, args, env, outWriter, errWriter)
 	if err != nil {
 		return nil, xerrors.Errorf("terraform plan: %w", err)
 	}
-	resources, err := e.planResources(ctx, planfilePath)
+	resources, err := e.planResources(ctx, killCtx, planfilePath)
 	if err != nil {
 		return nil, err
 	}
@@ -201,40 +226,52 @@ func (e executor) plan(ctx context.Context, env, vars []string, logr logger, des
 	}, nil
 }
 
-func (e executor) planResources(ctx context.Context, planfilePath string) ([]*proto.Resource, error) {
+func (e executor) planResources(ctx, killCtx context.Context, planfilePath string) ([]*proto.Resource, error) {
-	plan, err := e.showPlan(ctx, planfilePath)
+	plan, err := e.showPlan(ctx, killCtx, planfilePath)
 	if err != nil {
 		return nil, xerrors.Errorf("show terraform plan file: %w", err)
 	}
 
-	rawGraph, err := e.graph(ctx)
+	rawGraph, err := e.graph(ctx, killCtx)
 	if err != nil {
 		return nil, xerrors.Errorf("graph: %w", err)
 	}
 	return ConvertResources(plan.PlannedValues.RootModule, rawGraph)
 }
 
-func (e executor) showPlan(ctx context.Context, planfilePath string) (*tfjson.Plan, error) {
+func (e executor) showPlan(ctx, killCtx context.Context, planfilePath string) (*tfjson.Plan, error) {
 	args := []string{"show", "-json", "-no-color", planfilePath}
 	p := new(tfjson.Plan)
-	err := e.execParseJSON(ctx, args, e.basicEnv(), p)
+	err := e.execParseJSON(ctx, killCtx, args, e.basicEnv(), p)
 	return p, err
 }
 
-func (e executor) graph(ctx context.Context) (string, error) {
+func (e executor) graph(ctx, killCtx context.Context) (string, error) {
-	// #nosec
+	if ctx.Err() != nil {
-	cmd := exec.CommandContext(ctx, e.binaryPath, "graph")
+		return "", ctx.Err()
+	}
+
+	var out bytes.Buffer
+	cmd := exec.CommandContext(killCtx, e.binaryPath, "graph") // #nosec
+	cmd.Stdout = &out
 	cmd.Dir = e.workdir
 	cmd.Env = e.basicEnv()
-	out, err := cmd.Output()
+
+	err := cmd.Start()
+	if err != nil {
+		return "", err
+	}
+	interruptCommandOnCancel(ctx, killCtx, cmd)
+
+	err = cmd.Wait()
 	if err != nil {
 		return "", xerrors.Errorf("graph: %w", err)
 	}
-	return string(out), nil
+	return out.String(), nil
 }
 
 // revive:disable-next-line:flag-parameter
-func (e executor) apply(ctx context.Context, env, vars []string, logr logger, destroy bool,
+func (e executor) apply(ctx, killCtx context.Context, env, vars []string, logr logger, destroy bool,
 ) (*proto.Provision_Response, error) {
 	args := []string{
 		"apply",
@@ -258,11 +295,11 @@ func (e executor) apply(ctx context.Context, env, vars []string, logr logger, de
 		<-doneErr
 	}()
 
-	err := e.execWriteOutput(ctx, args, env, outWriter, errWriter)
+	err := e.execWriteOutput(ctx, killCtx, args, env, outWriter, errWriter)
 	if err != nil {
 		return nil, xerrors.Errorf("terraform apply: %w", err)
 	}
-	resources, err := e.stateResources(ctx)
+	resources, err := e.stateResources(ctx, killCtx)
 	if err != nil {
 		return nil, err
 	}
@@ -281,12 +318,12 @@ func (e executor) apply(ctx context.Context, env, vars []string, logr logger, de
 	}, nil
 }
 
-func (e executor) stateResources(ctx context.Context) ([]*proto.Resource, error) {
+func (e executor) stateResources(ctx, killCtx context.Context) ([]*proto.Resource, error) {
-	state, err := e.state(ctx)
+	state, err := e.state(ctx, killCtx)
 	if err != nil {
 		return nil, err
 	}
-	rawGraph, err := e.graph(ctx)
+	rawGraph, err := e.graph(ctx, killCtx)
 	if err != nil {
 		return nil, xerrors.Errorf("get terraform graph: %w", err)
 	}
@@ -300,16 +337,33 @@ func (e executor) stateResources(ctx context.Context) ([]*proto.Resource, error)
 	return resources, nil
 }
 
-func (e executor) state(ctx context.Context) (*tfjson.State, error) {
+func (e executor) state(ctx, killCtx context.Context) (*tfjson.State, error) {
 	args := []string{"show", "-json"}
 	state := &tfjson.State{}
-	err := e.execParseJSON(ctx, args, e.basicEnv(), state)
+	err := e.execParseJSON(ctx, killCtx, args, e.basicEnv(), state)
 	if err != nil {
 		return nil, xerrors.Errorf("terraform show state: %w", err)
 	}
 	return state, nil
 }
 
+func interruptCommandOnCancel(ctx, killCtx context.Context, cmd *exec.Cmd) {
+	go func() {
+		select {
+		case <-ctx.Done():
+			switch runtime.GOOS {
+			case "windows":
+				// Interrupts aren't supported by Windows.
+				_ = cmd.Process.Kill()
+			default:
+				_ = cmd.Process.Signal(os.Interrupt)
+			}
+
+		case <-killCtx.Done():
+		}
+	}()
+}
+
 type logger interface {
 	Log(*proto.Log) error
 }
@@ -381,9 +435,6 @@ func provisionReadAndLog(logr logger, reader io.Reader, done chan<- any) {
 
 		// If the diagnostic is provided, let's provide a bit more info!
 		logLevel = convertTerraformLogLevel(log.Diagnostic.Severity, logr)
-		if err != nil {
-			continue
-		}
 		err = logr.Log(&proto.Log{Level: logLevel, Output: log.Diagnostic.Detail})
 		if err != nil {
 			// Not much we can do.  We can't log because logging is itself breaking!

provisioner/terraform/parse_test.go

@@ -16,7 +16,7 @@ import (
 func TestParse(t *testing.T) {
 	t.Parallel()
 
-	ctx, api := setupProvisioner(t)
+	ctx, api := setupProvisioner(t, nil)
 
 	testCases := []struct {
 		Name     string
@@ -171,7 +171,7 @@ func TestParse(t *testing.T) {
 			// Write all files to the temporary test directory.
 			directory := t.TempDir()
 			for path, content := range testCase.Files {
-				err := os.WriteFile(filepath.Join(directory, path), []byte(content), 0600)
+				err := os.WriteFile(filepath.Join(directory, path), []byte(content), 0o600)
 				require.NoError(t, err)
 			}
 

provisioner/terraform/provision.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 
 	"golang.org/x/xerrors"
 
@@ -14,11 +15,7 @@ import (
 )
 
 // Provision executes `terraform apply` or `terraform plan` for dry runs.
-func (t *server) Provision(stream proto.DRPCProvisioner_ProvisionStream) error {
+func (s *server) Provision(stream proto.DRPCProvisioner_ProvisionStream) error {
-	logr := streamLogger{stream: stream}
-	shutdown, shutdownFunc := context.WithCancel(stream.Context())
-	defer shutdownFunc()
-
 	request, err := stream.Recv()
 	if err != nil {
 		return err
@@ -30,6 +27,33 @@ func (t *server) Provision(stream proto.DRPCProvisioner_ProvisionStream) error {
 	if request.GetStart() == nil {
 		return nil
 	}
+
+	// Create a context for graceful cancellation bound to the stream
+	// context. This ensures that we will perform graceful cancellation
+	// even on connection loss.
+	ctx, cancel := context.WithCancel(stream.Context())
+	defer cancel()
+
+	// Create a separate context for forcefull cancellation not tied to
+	// the stream so that we can control when to terminate the process.
+	killCtx, kill := context.WithCancel(context.Background())
+	defer kill()
+
+	// Ensure processes are eventually cleaned up on graceful
+	// cancellation or disconnect.
+	go func() {
+		<-stream.Context().Done()
+
+		// TODO(mafredri): We should track this provision request as
+		// part of graceful server shutdown procedure. Waiting on a
+		// process here should delay provisioner/coder shutdown.
+		select {
+		case <-time.After(s.exitTimeout):
+			kill()
+		case <-killCtx.Done():
+		}
+	}()
+
 	go func() {
 		for {
 			request, err := stream.Recv()
@@ -37,29 +61,28 @@ func (t *server) Provision(stream proto.DRPCProvisioner_ProvisionStream) error {
 				return
 			}
 			if request.GetCancel() == nil {
-				// This is only to process cancels!
+				// We only process cancellation requests here.
 				continue
 			}
-			shutdownFunc()
+			cancel()
 			return
 		}
 	}()
+
+	logr := streamLogger{stream: stream}
 	start := request.GetStart()
 
-	if err != nil {
+	e := s.executor(start.Directory)
-		return xerrors.Errorf("create new terraform executor: %w", err)
+	if err = e.checkMinVersion(ctx); err != nil {
-	}
-	e := t.executor(start.Directory)
-	if err := e.checkMinVersion(stream.Context()); err != nil {
 		return err
 	}
-	if err := logTerraformEnvVars(logr); err != nil {
+	if err = logTerraformEnvVars(logr); err != nil {
 		return err
 	}
 
 	statefilePath := filepath.Join(start.Directory, "terraform.tfstate")
 	if len(start.State) > 0 {
-		err := os.WriteFile(statefilePath, start.State, 0600)
+		err = os.WriteFile(statefilePath, start.State, 0o600)
 		if err != nil {
 			return xerrors.Errorf("write statefile %q: %w", statefilePath, err)
 		}
@@ -87,12 +110,21 @@ func (t *server) Provision(stream proto.DRPCProvisioner_ProvisionStream) error {
 		})
 	}
 
-	t.logger.Debug(shutdown, "running initialization")
+	s.logger.Debug(ctx, "running initialization")
-	err = e.init(stream.Context(), logr)
+	err = e.init(ctx, killCtx, logr)
 	if err != nil {
+		if ctx.Err() != nil {
+			return stream.Send(&proto.Provision_Response{
+				Type: &proto.Provision_Response_Complete{
+					Complete: &proto.Provision_Complete{
+						Error: err.Error(),
+					},
+				},
+			})
+		}
 		return xerrors.Errorf("initialize terraform: %w", err)
 	}
-	t.logger.Debug(shutdown, "ran initialization")
+	s.logger.Debug(ctx, "ran initialization")
 
 	env, err := provisionEnv(start)
 	if err != nil {
@@ -104,15 +136,15 @@ func (t *server) Provision(stream proto.DRPCProvisioner_ProvisionStream) error {
 	}
 	var resp *proto.Provision_Response
 	if start.DryRun {
-		resp, err = e.plan(shutdown, env, vars, logr,
+		resp, err = e.plan(ctx, killCtx, env, vars, logr,
 			start.Metadata.WorkspaceTransition == proto.WorkspaceTransition_DESTROY)
 	} else {
-		resp, err = e.apply(shutdown, env, vars, logr,
+		resp, err = e.apply(ctx, killCtx, env, vars, logr,
 			start.Metadata.WorkspaceTransition == proto.WorkspaceTransition_DESTROY)
 	}
 	if err != nil {
 		if start.DryRun {
-			if shutdown.Err() != nil {
+			if ctx.Err() != nil {
 				return stream.Send(&proto.Provision_Response{
 					Type: &proto.Provision_Response_Complete{
 						Complete: &proto.Provision_Complete{

provisioner/terraform/provision_test.go

@@ -5,11 +5,14 @@ package terraform_test
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"os"
 	"path/filepath"
+	"runtime"
 	"sort"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -22,7 +25,15 @@ import (
 	"github.com/coder/coder/provisionersdk/proto"
 )
 
-func setupProvisioner(t *testing.T) (context.Context, proto.DRPCProvisionerClient) {
+type provisionerServeOptions struct {
+	binaryPath  string
+	exitTimeout time.Duration
+}
+
+func setupProvisioner(t *testing.T, opts *provisionerServeOptions) (context.Context, proto.DRPCProvisionerClient) {
+	if opts == nil {
+		opts = &provisionerServeOptions{}
+	}
 	cachePath := t.TempDir()
 	client, server := provisionersdk.TransportPipe()
 	ctx, cancelFunc := context.WithCancel(context.Background())
@@ -39,18 +50,125 @@ func setupProvisioner(t *testing.T) (context.Context, proto.DRPCProvisionerClien
 			ServeOptions: &provisionersdk.ServeOptions{
 				Listener: server,
 			},
-			CachePath: cachePath,
+			BinaryPath:  opts.binaryPath,
-			Logger:    slogtest.Make(t, nil).Leveled(slog.LevelDebug),
+			CachePath:   cachePath,
+			Logger:      slogtest.Make(t, nil).Leveled(slog.LevelDebug),
+			ExitTimeout: opts.exitTimeout,
 		})
 	}()
 	api := proto.NewDRPCProvisionerClient(provisionersdk.Conn(client))
 	return ctx, api
 }
 
+func TestProvision_Cancel(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("This test uses interrupts and is not supported on Windows")
+	}
+
+	t.Parallel()
+
+	cwd, err := os.Getwd()
+	require.NoError(t, err)
+	fakeBin := filepath.Join(cwd, "testdata", "bin", "terraform_fake_cancel.sh")
+
+	tests := []struct {
+		name          string
+		mode          string
+		startSequence []string
+		wantLog       []string
+	}{
+		{
+			name:          "Cancel init",
+			mode:          "init",
+			startSequence: []string{"init_start"},
+			wantLog:       []string{"interrupt", "exit"},
+		},
+		{
+			name:          "Cancel apply",
+			mode:          "apply",
+			startSequence: []string{"init", "apply_start"},
+			wantLog:       []string{"interrupt", "exit"},
+		},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			dir := t.TempDir()
+			binPath := filepath.Join(dir, "terraform")
+
+			// Example: exec /path/to/terrafork_fake_cancel.sh 1.2.1 apply "$@"
+			content := fmt.Sprintf("#!/bin/sh\nexec %q %s %s \"$@\"\n", fakeBin, terraform.TerraformVersion.String(), tt.mode)
+			err = os.WriteFile(binPath, []byte(content), 0o755) //#nosec
+			require.NoError(t, err)
+
+			ctx, api := setupProvisioner(t, &provisionerServeOptions{
+				binaryPath:  binPath,
+				exitTimeout: time.Nanosecond,
+			})
+
+			response, err := api.Provision(ctx)
+			require.NoError(t, err)
+			err = response.Send(&proto.Provision_Request{
+				Type: &proto.Provision_Request_Start{
+					Start: &proto.Provision_Start{
+						Directory: dir,
+						DryRun:    false,
+						ParameterValues: []*proto.ParameterValue{{
+							DestinationScheme: proto.ParameterDestination_PROVISIONER_VARIABLE,
+							Name:              "A",
+							Value:             "example",
+						}},
+						Metadata: &proto.Provision_Metadata{},
+					},
+				},
+			})
+			require.NoError(t, err)
+
+			for _, line := range tt.startSequence {
+			LoopStart:
+				msg, err := response.Recv()
+				require.NoError(t, err)
+
+				t.Log(msg.Type)
+
+				log := msg.GetLog()
+				if log == nil {
+					goto LoopStart
+				}
+				require.Equal(t, line, log.Output)
+			}
+
+			err = response.Send(&proto.Provision_Request{
+				Type: &proto.Provision_Request_Cancel{
+					Cancel: &proto.Provision_Cancel{},
+				},
+			})
+			require.NoError(t, err)
+
+			var gotLog []string
+			for {
+				msg, err := response.Recv()
+				require.NoError(t, err)
+
+				if log := msg.GetLog(); log != nil {
+					gotLog = append(gotLog, log.Output)
+				}
+				if c := msg.GetComplete(); c != nil {
+					require.Contains(t, c.Error, "exit status 1")
+					break
+				}
+			}
+			require.Equal(t, tt.wantLog, gotLog)
+		})
+	}
+}
+
 func TestProvision(t *testing.T) {
 	t.Parallel()
 
-	ctx, api := setupProvisioner(t)
+	ctx, api := setupProvisioner(t, nil)
 
 	testCases := []struct {
 		Name    string
@@ -209,7 +327,7 @@ func TestProvision(t *testing.T) {
 
 			directory := t.TempDir()
 			for path, content := range testCase.Files {
-				err := os.WriteFile(filepath.Join(directory, path), []byte(content), 0600)
+				err := os.WriteFile(filepath.Join(directory, path), []byte(content), 0o600)
 				require.NoError(t, err)
 			}
 
@@ -302,11 +420,11 @@ func TestProvision_ExtraEnv(t *testing.T) {
 	t.Setenv("TF_LOG", "INFO")
 	t.Setenv("TF_SUPERSECRET", secretValue)
 
-	ctx, api := setupProvisioner(t)
+	ctx, api := setupProvisioner(t, nil)
 
 	directory := t.TempDir()
 	path := filepath.Join(directory, "main.tf")
-	err := os.WriteFile(path, []byte(`resource "null_resource" "A" {}`), 0600)
+	err := os.WriteFile(path, []byte(`resource "null_resource" "A" {}`), 0o600)
 	require.NoError(t, err)
 
 	request := &proto.Provision_Request{

provisioner/terraform/serve.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"path/filepath"
 	"sync"
+	"time"
 
 	"github.com/cli/safeexec"
 	"github.com/hashicorp/go-version"
@@ -15,26 +16,20 @@ import (
 	"github.com/coder/coder/provisionersdk"
 )
 
-// This is the exact version of Terraform used internally
-// when Terraform is missing on the system.
-var terraformVersion = version.Must(version.NewVersion("1.2.1"))
-var minTerraformVersion = version.Must(version.NewVersion("1.1.0"))
-var maxTerraformVersion = version.Must(version.NewVersion("1.2.1"))
-
 var (
-	// The minimum version of Terraform supported by the provisioner.
+	// TerraformVersion is the version of Terraform used internally
-	// Validation came out in 0.13.0, which was released August 10th, 2020.
+	// when Terraform is not available on the system.
-	// https://www.hashicorp.com/blog/announcing-hashicorp-terraform-0-13
+	TerraformVersion = version.Must(version.NewVersion("1.2.1"))
-	minimumTerraformVersion = func() *version.Version {
+
-		v, err := version.NewSemver("0.13.0")
+	minTerraformVersion = version.Must(version.NewVersion("1.1.0"))
-		if err != nil {
+	maxTerraformVersion = version.Must(version.NewVersion("1.2.1"))
-			panic(err)
+
-		}
+	terraformMinorVersionMismatch = xerrors.New("Terraform binary minor version mismatch.")
-		return v
-	}()
 )
 
-var terraformMinorVersionMismatch = xerrors.New("Terraform binary minor version mismatch.")
+const (
+	defaultExitTimeout = 5 * time.Minute
+)
 
 type ServeOptions struct {
 	*provisionersdk.ServeOptions
@@ -44,6 +39,17 @@ type ServeOptions struct {
 	BinaryPath string
 	CachePath  string
 	Logger     slog.Logger
+
+	// ExitTimeout defines how long we will wait for a running Terraform
+	// command to exit (cleanly) if the provision was stopped. This only
+	// happens when the command is still running after the provision
+	// stream is closed. If the provision is canceled via RPC, this
+	// timeout will not be used.
+	//
+	// This is a no-op on Windows where the process can't be interrupted.
+	//
+	// Default value: 5 minutes.
+	ExitTimeout time.Duration
 }
 
 func absoluteBinaryPath(ctx context.Context) (string, error) {
@@ -90,7 +96,7 @@ func Serve(ctx context.Context, options *ServeOptions) error {
 			installer := &releases.ExactVersion{
 				InstallDir: options.CachePath,
 				Product:    product.Terraform,
-				Version:    terraformVersion,
+				Version:    TerraformVersion,
 			}
 
 			execPath, err := installer.Install(ctx)
@@ -102,10 +108,14 @@ func Serve(ctx context.Context, options *ServeOptions) error {
 			options.BinaryPath = absoluteBinary
 		}
 	}
+	if options.ExitTimeout == 0 {
+		options.ExitTimeout = defaultExitTimeout
+	}
 	return provisionersdk.Serve(ctx, &server{
-		binaryPath: options.BinaryPath,
+		binaryPath:  options.BinaryPath,
-		cachePath:  options.CachePath,
+		cachePath:   options.CachePath,
-		logger:     options.Logger,
+		logger:      options.Logger,
+		exitTimeout: options.ExitTimeout,
 	}, options.ServeOptions)
 }
 
@@ -117,6 +127,8 @@ type server struct {
 	binaryPath string
 	cachePath  string
 	logger     slog.Logger
+
+	exitTimeout time.Duration
 }
 
 func (s *server) executor(workdir string) executor {

provisioner/terraform/testdata/bin/terraform_fake_cancel.sh

@@ -0,0 +1,60 @@
+#!/bin/sh
+
+VERSION=$1
+MODE=$2
+shift 2
+
+json_print() {
+	echo "{\"@level\":\"error\",\"@message\":\"$*\"}"
+}
+
+case "$1" in
+version)
+	cat <<-EOF
+		{
+			"terraform_version": "${VERSION}",
+			"platform": "linux_amd64",
+			"provider_selections": {},
+			"terraform_outdated": false
+		}
+	EOF
+	exit 0
+	;;
+init)
+	case "$MODE" in
+	apply)
+		echo "init"
+		;;
+	init)
+		sleep 10 &
+		sleep_pid=$!
+
+		trap 'echo exit; kill -9 $sleep_pid 2>/dev/null' EXIT
+		trap 'echo interrupt; exit 1' INT
+		trap 'echo terminate"; exit 2' TERM
+
+		echo init_start
+		wait
+		echo init_end
+		;;
+	esac
+	;;
+apply)
+	sleep 10 &
+	sleep_pid=$!
+
+	trap 'json_print exit; kill -9 $sleep_pid 2>/dev/null' EXIT
+	trap 'json_print interrupt; exit 1' INT
+	trap 'json_print terminate"; exit 2' TERM
+
+	json_print apply_start
+	wait
+	json_print apply_end
+	;;
+plan)
+	echo "plan not supported"
+	exit 1
+	;;
+esac
+
+exit 0