Add -ignore-no-changes to change no changes on plan exit code.

Previously if no changes were detected on a deployment Levant
would exit with status 1 which caused some CI/CD pipeline issues.

This change allows users to change this behaviouer using the flag
whereby if no changes are detected, Levant will exit with a status
code 0.

Closes #186

command/deploy.go

@@ -24,11 +24,11 @@ func (c *DeployCommand) Help() string {
 	helpText := `
 Usage: levant deploy [options] [TEMPLATE]
 
-	Deploy a Nomad job based on input templates and variable files. The deploy 
-	command supports passing variables individually on the command line. Multiple
-	commands can be passed in the format of -var 'key=value'. Variables passed 
-	via the command line take precedence over the same variable declared within 
-	a passed variable file.
+  Deploy a Nomad job based on input templates and variable files. The deploy
+  command supports passing variables individually on the command line. Multiple
+  commands can be passed in the format of -var 'key=value'. Variables passed
+  via the command line take precedence over the same variable declared within
+  a passed variable file.
 
 Arguments:
 
@@ -57,6 +57,12 @@ General Options:
     Use the taskgroup count from the Nomad jobfile instead of the count that
     is currently set in a running job.
 
+  -ignore-no-changes
+    By default if no changes are detected when running a deployment Levant will
+    exit with a status 1 to indicate a deployment didn't happen. This behaviour
+    can be changed using this flag so that Levant will exit cleanly ensuring CD
+    pipelines don't fail when no changes are detected.
+
   -log-level=<level>
     Specify the verbosity level of Levant's logs. Valid values include DEBUG,
     INFO, and WARN, in decreasing order of verbosity. The default is INFO.
@@ -68,7 +74,7 @@ General Options:
   -var-file=<file>
     Used in conjunction with the -job-file will deploy a templated job to your
     Nomad cluster. You can repeat this flag multiple times to supply multiple var-files.
-	[default: levant.(yaml|yml|tf)]
+    [default: levant.(yaml|yml|tf)]
 `
 	return strings.TrimSpace(helpText)
 }
@@ -93,6 +99,7 @@ func (c *DeployCommand) Run(args []string) int {
 	flags.StringVar(&addr, "consul-address", "", "")
 	flags.BoolVar(&config.ForceBatch, "force-batch", false, "")
 	flags.BoolVar(&config.ForceCount, "force-count", false, "")
+	flags.BoolVar(&config.IgnoreNoChanges, "ignore-no-changes", false, "")
 	flags.StringVar(&config.LogLevel, "log-level", "INFO", "")
 	flags.StringVar(&config.LogFormat, "log-format", "HUMAN", "")
 	flags.Var((*helper.FlagStringSlice)(&config.VariableFiles), "var-file", "")

levant/deploy.go

@@ -54,9 +54,27 @@ func TriggerDeployment(config *structs.Config, nomadClient *nomad.Client) bool {
 		return false
 	}
 
-	preDep := levantDep.preDeploy()
-	if !preDep {
-		log.Error().Msg("levant/deploy: pre-deployment process failed")
+	// Run the job validation steps and count updater.
+	preDepVal := levantDep.preDeployValidate()
+	if !preDepVal {
+		log.Error().Msg("levant/deploy: pre-deployment validation process failed")
+		return false
+	}
+
+	// Run the plan functionality and return if an error occurred during the run.
+	// This would have already been logged, so its just used to control the flow
+	// and pass the correct signal up the stack.
+	c, err := levantDep.plan()
+	if err != nil {
+		return false
+	}
+
+	// If no changes were detected, see whether the user wants to exit cleanly
+	// or wants to exit 1 if no changes were detected. GH-186.
+	if !c {
+		if levantDep.config.IgnoreNoChanges {
+			return true
+		}
 		return false
 	}
 
@@ -71,7 +89,7 @@ func TriggerDeployment(config *structs.Config, nomadClient *nomad.Client) bool {
 	return true
 }
 
-func (l *levantDeployment) preDeploy() (success bool) {
+func (l *levantDeployment) preDeployValidate() (success bool) {
 
 	// Validate the job to check it is syntactically correct.
 	if _, _, err := l.nomad.Jobs().Validate(l.config.Job, nil); err != nil {
@@ -92,12 +110,6 @@ func (l *levantDeployment) preDeploy() (success bool) {
 		}
 	}
 
-	// Trigger a Nomad plan and Levants functionality to log all planned changes
-	// upon job registration.
-	if !l.plan() {
-		return
-	}
-
 	return true
 }
 

levant/plan.go

@@ -17,15 +17,15 @@ var (
 // plan is the entry point into running the Levant plan function which logs all
 // changes anticipated by Nomad of the upcoming job registration. If there are
 // no planned changes here, return false to indicate we should stop the process.
-func (l *levantDeployment) plan() bool {
+func (l *levantDeployment) plan() (bool, error) {
 
 	log.Debug().Msg("levant/plan: triggering Nomad plan")
 
 	// Run a plan using the rendered job.
 	resp, _, err := l.nomad.Jobs().Plan(l.config.Job, true, nil)
 	if err != nil {
 		log.Error().Err(err).Msg("levant/plan: unable to run a job plan")
-		return false
+		return false, err
 	}
 
 	switch resp.Diff.Type {
@@ -34,21 +34,21 @@ func (l *levantDeployment) plan() bool {
 	// is a new registration.
 	case diffTypeAdded:
 		log.Info().Msg("levant/plan: job is a new addition to the cluster")
-		return true
+		return true, nil
 
 	// If there are no changes, then log an error so the user can see this and
 	// exit the deployment.
 	case diffTypeNone:
 		log.Error().Msg("levant/plan: no changes detected for job")
-		return false
+		return false, nil
 
 	// If there are changes, run the planDiff function which is responsible for
 	// iterating through the plan and logging all the planned changes.
 	case diffTypeEdited:
 		planDiff(resp.Diff)
 	}
 
-	return true
+	return true, nil
 }
 
 func planDiff(plan *nomad.JobDiff) {

levant/structs/config.go

@@ -27,6 +27,10 @@ type Config struct {
 	// and force the count based on the rendered job file.
 	ForceCount bool
 
+	// IgnoreNoChanges is used to allow operators to force Levant to exit cleanly
+	// even if there are no changes found during the plan.
+	IgnoreNoChanges bool
+
 	// Job represents the Nomad Job definition that will be deployed.
 	Job *nomad.Job