Experimental feature to help with terraform state migrations (#175)

cmd/exp/exp.go

@@ -0,0 +1,11 @@
+package exp
+
+import "github.com/spf13/cobra"
+
+// ExpCmd is a subcommand for experimental commands
+var ExpCmd = &cobra.Command{
+	Use:          "exp",
+	Short:        "Experimental commands",
+	Long:         "Grouping of experimental commands. These are experimental and prone to change",
+	SilenceUsage: true,
+}

cmd/exp/migrate.go

@@ -0,0 +1,20 @@
+package exp
+
+import (
+	"github.com/chanzuckerberg/fogg/exp/migrate"
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	ExpCmd.AddCommand(migrateCmd)
+}
+
+var migrateCmd = &cobra.Command{
+	Use:   "migrate",
+	Short: "Assists with terraform state migrations",
+	Long: `This command aims to assist with terraform state migrations.
+	Particularly when there are module renames and such.`,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		return migrate.Migrate("plan.tfplan")
+	},
+}

cmd/root.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 
+	"github.com/chanzuckerberg/fogg/cmd/exp"
 	"github.com/chanzuckerberg/fogg/errs"
 	"github.com/fatih/color"
 	"github.com/spf13/cobra"
@@ -17,6 +18,8 @@ var (
 func init() {
 	rootCmd.PersistentFlags().BoolVar(&debug, "debug", false, "enable verbose output")
 	rootCmd.PersistentFlags().BoolVarP(&quiet, "quiet", "q", false, "do not output to console; use return code to determine success/failure")
+
+	rootCmd.AddCommand(exp.ExpCmd)
 }
 
 var rootCmd = &cobra.Command{

exp/migrate/migrate.go

@@ -0,0 +1,114 @@
+package migrate
+
+import (
+	"fmt"
+	"math"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/antzucaro/matchr"
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/hashicorp/terraform/terraform"
+	"github.com/pkg/errors"
+	"github.com/segmentio/go-prompt"
+	log "github.com/sirupsen/logrus"
+)
+
+func generatePlan(planPath string) error {
+	cmd := exec.Command("make", "init")
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	err := cmd.Run()
+	if err != nil {
+		errors.Wrap(err, "Could not run make init")
+	}
+
+	cmd = exec.Command("make", "run")
+	cmd.Env = append(cmd.Env, fmt.Sprintf("plan -out %s", planPath))
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+
+	err = cmd.Run()
+	return errors.Wrap(err, "Could not run terraform plan")
+}
+
+// parsePlan
+func parsePlan(planPath string) error {
+	f, err := os.Open(planPath)
+	if err != nil {
+		return errors.Wrapf(err, "Could not read plan at %s", planPath)
+	}
+	defer f.Close()
+	// TODO: also remove the plan?
+
+	plan, err := terraform.ReadPlan(f)
+	if err != nil {
+		return errors.Wrapf(err, "Terraform could not parse plan at %s", planPath)
+	}
+	if plan.Diff == nil {
+		log.Debug("nil diff")
+		return nil
+	}
+
+	deletions := map[string]bool{}
+	additions := map[string]bool{}
+
+	for _, module := range plan.Diff.Modules {
+		moduleName := strings.TrimPrefix(strings.Join(module.Path, "."), "root.")
+		for name, instance := range module.Resources {
+			fullName := fmt.Sprintf("%s.%s", moduleName, name)
+			if instance.Destroy {
+				deletions[fullName] = true
+			} else {
+				additions[fullName] = true
+			}
+		}
+	}
+
+	for addition := range additions {
+		currScore := math.MaxInt64
+		var replace *string
+
+		for deletion, ok := range deletions {
+			if !ok {
+				continue
+			}
+			score := matchr.DamerauLevenshtein(addition, deletion)
+			if score < currScore {
+				currScore = score
+				replace = aws.String(deletion)
+			}
+		}
+
+		if replace == nil {
+			continue
+		}
+
+		if !prompt.Confirm("Would you like us to move %s to %s", *replace, addition) {
+			continue
+		}
+
+		deletions[*replace] = false
+		cmd := exec.Command("make", "run")
+		cmd.Stdin = os.Stdin
+		cmd.Stdout = os.Stdout
+		cmd.Env = append(cmd.Env, fmt.Sprintf("CMD=state mv %s %s", *replace, addition))
+
+		err = cmd.Run()
+		if err != nil {
+			return errors.Wrapf(err, "Could not move %s to %s", *replace, addition)
+		}
+	}
+	return nil
+}
+
+// Migrate migrates
+func Migrate(planPath string) error {
+	defer os.Remove(planPath)
+	err := generatePlan(planPath)
+	if err != nil {
+		return err
+	}
+	return parsePlan(planPath)
+}