Merge pull request #4 from Pix4D/reduce-diff-noise

real-life experience: reduce diff noise, do not take state lock

Author: marco-m-pix4d

CHANGELOG.md

@@ -18,6 +18,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changes
 
+- Migration script: do not print any more the count `>>> 1/N`, because each time N changed, this was causing N spurious diffs, hiding the real elements that changed. The `terravalet_output_format` is now 2.
+- Migration script: do not take a lock; it is useless as long as the operations are strictly on a local state file. This speeds up the runtime.
+
 ### New
 
 - Generate also the DOWN migration script.

main.go

@@ -170,13 +170,15 @@ func match(create, destroy []string) (map[string]string, map[string]string, erro
 func script(matches map[string]string, statePath string, out io.Writer) error {
 	fmt.Fprintf(out, "#! /usr/bin/sh\n")
 	fmt.Fprintf(out, "# DO NOT EDIT. Generated by terravalet.\n")
-	fmt.Fprintf(out, "# terravalet_output_format=1\n")
+	fmt.Fprintf(out, "# terravalet_output_format=2\n")
 	fmt.Fprintf(out, "#\n")
 	fmt.Fprintf(out, "# This script will move %d items.\n\n", len(matches))
 	fmt.Fprintf(out, "set -e\n\n")
 
-	cmd := fmt.Sprintf("terraform state mv -state=%s", statePath)
-	total := len(matches)
+	// -lock=false greatly speeds up operations when the state has many elements
+	// and is safe as long as we use -state=FILE, since this keeps operations
+	// strictly local, without considering the configured backend.
+	cmd := fmt.Sprintf("terraform state mv -lock=false -state=%s", statePath)
 
 	// Go maps are unordered. We want instead a stable iteration order, to make it
 	// possible to compare scripts.
@@ -188,7 +190,6 @@ func script(matches map[string]string, statePath string, out io.Writer) error {
 
 	i := 1
 	for _, d := range destroys {
-		fmt.Fprintf(out, "echo \">>> %d/%d\"\n", i, total)
 		fmt.Fprintf(out, "%s \\\n    '%s' \\\n    '%s'\n\n", cmd, d, matches[d])
 		i++
 	}

testdata/001_synthetic.down.sh

@@ -1,23 +1,20 @@
 #! /usr/bin/sh
 # DO NOT EDIT. Generated by terravalet.
-# terravalet_output_format=1
+# terravalet_output_format=2
 #
 # This script will move 3 items.
 
 set -e
 
-echo ">>> 1/3"
-terraform state mv -state=local.tfstate \
+terraform state mv -lock=false -state=local.tfstate \
     'aws_batch_compute_environment.concourse_gpu_batch' \
     'module.ci.aws_batch_compute_environment.concourse_gpu_batch'
 
-echo ">>> 2/3"
-terraform state mv -state=local.tfstate \
+terraform state mv -lock=false -state=local.tfstate \
     'aws_instance.bar' \
     'module.ci.aws_instance.bar'
 
-echo ">>> 3/3"
-terraform state mv -state=local.tfstate \
+terraform state mv -lock=false -state=local.tfstate \
     'aws_instance.foo["cloud"]' \
     'module.ci.aws_instance.foo["cloud"]'
 

testdata/001_synthetic.up.sh

@@ -1,23 +1,20 @@
 #! /usr/bin/sh
 # DO NOT EDIT. Generated by terravalet.
-# terravalet_output_format=1
+# terravalet_output_format=2
 #
 # This script will move 3 items.
 
 set -e
 
-echo ">>> 1/3"
-terraform state mv -state=local.tfstate \
+terraform state mv -lock=false -state=local.tfstate \
     'module.ci.aws_batch_compute_environment.concourse_gpu_batch' \
     'aws_batch_compute_environment.concourse_gpu_batch'
 
-echo ">>> 2/3"
-terraform state mv -state=local.tfstate \
+terraform state mv -lock=false -state=local.tfstate \
     'module.ci.aws_instance.bar' \
     'aws_instance.bar'
 
-echo ">>> 3/3"
-terraform state mv -state=local.tfstate \
+terraform state mv -lock=false -state=local.tfstate \
     'module.ci.aws_instance.foo["cloud"]' \
     'aws_instance.foo["cloud"]'