feat: add 'ftl serve' command for local dev (#497)

Fixes #470 

```bash
ftl serve --help
Usage: ftl serve

Start the FTL server.

Flags:
  -h, --help           Show context-sensitive help.
      --version        Show version.
      --config=FILE    Load configuration from TOML file.
      --endpoint=http://127.0.0.1:8892
                       FTL endpoint to bind/connect to ($FTL_ENDPOINT).
      --authenticators=HOST=EXE,…
                       Authenticators to use for FTL endpoints
                       ($FTL_AUTHENTICATORS).

Logging:
  --log-level=info    Log level ($LOG_LEVEL).
  --log-json          Log in JSON format ($LOG_JSON).

Command flags:
      --bind=http://localhost:8892
                             Starting endpoint to bind to and advertise to. Each
                             controller and runner will increment the port by 1
  -c, --num-controllers=1    Number of controllers to start.
  -r, --num-runners=10       Number of runners to start.
```

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

backend/runner/runner.go

@@ -41,7 +41,7 @@ type Config struct {
 	ControllerEndpoint *url.URL        `name:"ftl-endpoint" help:"Controller endpoint." env:"FTL_ENDPOINT" default:"http://localhost:8892"`
 	TemplateDir        string          `help:"Template directory to copy into each deployment, if any." type:"existingdir"`
 	DeploymentDir      string          `help:"Directory to store deployments in." default:"${deploymentdir}"`
-	Language           []string        `short:"l" help:"Languages the runner supports." env:"FTL_LANGUAGE" required:""`
+	Language           []string        `short:"l" help:"Languages the runner supports." env:"FTL_LANGUAGE" default:"go,kotlin"`
 	HeartbeatPeriod    time.Duration   `help:"Minimum period between heartbeats." default:"3s"`
 	HeartbeatJitter    time.Duration   `help:"Jitter to add to heartbeat period." default:"2s"`
 }

cmd/ftl/cmd_serve.go

@@ -2,14 +2,112 @@ package main
 
 import (
 	"context"
+	"encoding/binary"
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
 
+	"github.com/alecthomas/errors"
+	"github.com/alecthomas/kong"
+	"golang.org/x/sync/errgroup"
+
+	"github.com/TBD54566975/ftl/backend/common/log"
 	"github.com/TBD54566975/ftl/backend/controller"
+	"github.com/TBD54566975/ftl/backend/runner"
 )
 
 type serveCmd struct {
-	controller.Config
+	Bind        *url.URL `help:"Starting endpoint to bind to and advertise to. Each controller and runner will increment the port by 1" default:"http://localhost:8892"`
+	Controllers int      `short:"c" help:"Number of controllers to start." default:"1"`
+	Runners     int      `short:"r" help:"Number of runners to start." default:"10"`
 }
 
 func (s *serveCmd) Run(ctx context.Context) error {
-	return controller.Start(ctx, s.Config)
+	logger := log.FromContext(ctx)
+	logger.Infof("Starting %d controller(s) and %d runner(s)", s.Controllers, s.Runners)
+
+	wg, ctx := errgroup.WithContext(ctx)
+
+	controllerAddresses := make([]*url.URL, 0, s.Controllers)
+	nextBind := s.Bind
+
+	for i := 0; i < s.Controllers; i++ {
+		controllerAddresses = append(controllerAddresses, nextBind)
+		config := controller.Config{
+			Bind: nextBind,
+		}
+		if err := kong.ApplyDefaults(&config); err != nil {
+			return errors.WithStack(err)
+		}
+
+		scope := fmt.Sprintf("controller-%d", i)
+		controllerCtx := log.ContextWithLogger(ctx, logger.Scope(scope))
+
+		wg.Go(func() error { return controller.Start(controllerCtx, config) })
+
+		var err error
+		nextBind, err = incrementPort(nextBind)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+	}
+
+	cacheDir, err := os.UserCacheDir()
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	for i := 0; i < s.Runners; i++ {
+		controllerEndpoint := controllerAddresses[i%len(controllerAddresses)]
+		fmt.Printf("controllerEndpoint: %s runner: %s\n", controllerEndpoint, nextBind)
+		config := runner.Config{
+			Bind:               nextBind,
+			ControllerEndpoint: controllerEndpoint,
+		}
+
+		name := fmt.Sprintf("runner%d", i)
+		if err := kong.ApplyDefaults(&config, kong.Vars{
+			"deploymentdir": filepath.Join(cacheDir, "ftl-runner", name, "deployments"),
+			"language":      "go,kotlin",
+		}); err != nil {
+			return errors.WithStack(err)
+		}
+
+		// Create a readable ULID for the runner.
+		var ulid [16]byte
+		binary.BigEndian.PutUint32(ulid[10:], uint32(i))
+		ulidStr := fmt.Sprintf("%025X", ulid)
+		err := config.Key.Scan(ulidStr)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+
+		runnerCtx := log.ContextWithLogger(ctx, logger.Scope(name))
+
+		wg.Go(func() error { return runner.Start(runnerCtx, config) })
+
+		nextBind, err = incrementPort(nextBind)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+	}
+
+	if err := wg.Wait(); err != nil {
+		return errors.WithStack(err)
+	}
+	return nil
+}
+
+func incrementPort(baseURL *url.URL) (*url.URL, error) {
+	newURL := *baseURL
+
+	newPort, err := strconv.Atoi(newURL.Port())
+	if err != nil {
+		return nil, errors.WithStack(err)
+	}
+
+	newURL.Host = fmt.Sprintf("%s:%d", baseURL.Hostname(), newPort+1)
+	return &newURL, nil
 }