subcmd/apply: Support fail-safe approach (#185)

Up until now, the `apply` command implemented a fail-fast
strategy. This means that an attempt to configure a batch
of topics (by passing a path to a folder contains a list
of topics configurations files) will be terminated upon
the first failure (w/o even trying to apply the configuration
for the next-in-line topics).
This commit introduces the fail-safe support:
It allows the user to run the `apply` command in a fail-safe
manner, which means that instead of failing upon the first
failure, we'll simply continue to the next topic configuration,
while aggregating all the errors along the way.
Eventually, if there were any errors, all of them will be shown.

Signed-off-by: shimon-armis <[email protected]>

cmd/topicctl/subcmd/apply.go

@@ -37,6 +37,7 @@ type applyCmdConfig struct {
 	skipConfirm                  bool
 	ignoreFewerPartitionsError   bool
 	sleepLoopDuration            time.Duration
+	failFast                     bool
 
 	shared sharedOptions
 
@@ -112,6 +113,12 @@ func init() {
 		10*time.Second,
 		"Amount of time to wait between partition checks",
 	)
+	applyCmd.Flags().BoolVar(
+		&applyConfig.failFast,
+		"fail-fast",
+		true,
+		"Fail upon the first error encountered during apply process",
+	)
 
 	addSharedConfigOnlyFlags(applyCmd, &applyConfig.shared)
 	RootCmd.AddCommand(applyCmd)
@@ -132,6 +139,14 @@ func applyPreRun(cmd *cobra.Command, args []string) error {
 	return nil
 }
 
+func appendError(aggregatedErr error, err error) error {
+	if aggregatedErr == nil {
+		return err
+	}
+
+	return fmt.Errorf("%v\n%v", aggregatedErr, err)
+}
+
 func applyRun(cmd *cobra.Command, args []string) error {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -145,6 +160,8 @@ func applyRun(cmd *cobra.Command, args []string) error {
 
 	// Keep a cache of the admin clients with the cluster config path as the key
 	adminClients := map[string]admin.Client{}
+	// Keep track of any errors that occur during the apply process
+	var errs error
 
 	defer func() {
 		for _, adminClient := range adminClients {
@@ -167,7 +184,10 @@ func applyRun(cmd *cobra.Command, args []string) error {
 		for _, match := range matches {
 			matchCount++
 			if err := applyTopic(ctx, match, adminClients); err != nil {
-				return err
+				if applyConfig.failFast {
+					return err
+				}
+				errs = appendError(errs, err)
 			}
 		}
 	}
@@ -176,7 +196,7 @@ func applyRun(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("No topic configs match the provided args (%+v)", args)
 	}
 
-	return nil
+	return errs
 }
 
 func applyTopic(