mesh-controller/cmd/mesh-control/main.go

// Command mesh-control is the control plane: everything that needs to know about more than one
// node (novox/hq ADR 0006).
//
// It runs as one process holding several contexts, each owning its own store. Today it holds one,
// `inventory`, and does one thing with it — brings its schema up to date, which is step 3 of the
// bootstrap in novox/hq 07-the-substrate and the step the first node cannot get past without.
package main

import (
	"context"
	"fmt"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/novox/mesh-control/internal/inventory"
	"github.com/novox/mesh-control/internal/store"
)

// version is stamped at link time. Unset in a development build, and it says so rather than
// claiming a number.
var version = "development build"

// held is a context this process was granted, and the schema it carries.
//
// novox/hq ADR 0006 names seven. One is built. The list is short because the others do not exist
// yet, not because they are optional.
var held = []struct {
	name       string
	migrations func() ([]store.Migration, error)
}{
	{inventory.Name, inventory.Migrations},
}

func main() {
	if err := run(); err != nil {
		fmt.Fprintf(os.Stderr, "mesh-control: %v\n", err)
		os.Exit(1)
	}
}

func run() error {
	args := os.Args[1:]
	if len(args) == 0 {
		usage()
		return fmt.Errorf("no command given")
	}

	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()

	switch args[0] {
	case "migrate":
		return migrate(ctx)
	case "version":
		fmt.Println(version)
		return nil
	case "help", "-h", "--help":
		usage()
		return nil
	default:
		usage()
		return fmt.Errorf("%q is not a command", args[0])
	}
}

func usage() {
	fmt.Fprint(os.Stderr, `mesh-control — the control plane

  migrate    bring each context's schema up to date
  version    what this binary is

Each context reaches its own store through its own credential (novox/hq ADR 0008), named
`+store.Variable("<context>")+`. This process holds:

`)
	for _, c := range held {
		fmt.Fprintf(os.Stderr, "  %-12s database %-12s from %s\n",
			c.name, store.Database(c.name), store.Variable(c.name))
	}
	fmt.Fprintln(os.Stderr)
}

// migrate brings every held context's schema up to date.
//
// Reported per context and per migration, because this runs during a bootstrap on a machine with
// nothing else on it — the output is the only account of what happened, and "migrated" is not one.
func migrate(ctx context.Context) error {
	for _, c := range held {
		migrations, err := c.migrations()
		if err != nil {
			return err
		}

		s, err := store.Open(ctx, c.name)
		if err != nil {
			return err
		}
		defer s.Close()

		// The bootstrap raises PostgreSQL moments before this runs, and a container that is
		// running is not a database that will answer — a distinction this project has already
		// paid for once, when a crash-looping database reported itself as up between restarts.
		if err := s.Ready(ctx, 60*time.Second); err != nil {
			return err
		}

		done, err := s.Migrate(ctx, migrations)
		for _, m := range done {
			fmt.Printf("%s: applied %04d-%s\n", c.name, m.Number, m.Name)
		}
		if err != nil {
			return err
		}
		if len(done) == 0 {
			applied, err := s.AppliedMigrations(ctx)
			if err != nil {
				return err
			}
			fmt.Printf("%s: already up to date — %d migration(s)\n", c.name, len(applied))
		}
	}
	return nil
}