Add support for preflight check configuration (#900)

This adds configuration file support (`preflightRules`) for preflight
checks. Each preflight check must add a `SetConfig()` method to
accept configuration from the Preflight registry.

Signed-off-by: Todd Short <todd.short@me.com>

pkg/kapp/cmd/app/deploy.go

@@ -200,6 +200,10 @@ func (o *DeployOptions) Run() error {
 	}
 
 	if o.PreflightChecks != nil {
+		err = o.PreflightChecks.SetConfig(conf.PreflightRules())
+		if err != nil {
+			return fmt.Errorf("preflight configuration settings failed: %w", err)
+		}
 		err = o.PreflightChecks.Run(context.Background(), clusterChangesGraph)
 		if err != nil {
 			return fmt.Errorf("preflight checks failed: %w", err)

pkg/kapp/config/conf.go

@@ -155,6 +155,14 @@ func (c Conf) TemplateRules() []TemplateRule {
 	return result
 }
 
+func (c Conf) PreflightRules() []PreflightRule {
+	var result []PreflightRule
+	for _, config := range c.configs {
+		result = append(result, config.PreflightRules...)
+	}
+	return result
+}
+
 func (c Conf) DiffMaskRules() []DiffMaskRule {
 	var result []DiffMaskRule
 	for _, config := range c.configs {

pkg/kapp/config/config.go

@@ -30,6 +30,7 @@ type Config struct {
 	LabelScopingRules   []LabelScopingRule
 	TemplateRules       []TemplateRule
 	DiffMaskRules       []DiffMaskRule
+	PreflightRules      []PreflightRule
 
 	AdditionalLabels                          map[string]string
 	DiffAgainstLastAppliedFieldExclusionRules []DiffAgainstLastAppliedFieldExclusionRule
@@ -145,6 +146,11 @@ type ChangeRuleBinding struct {
 	ResourceMatchers []ResourceMatcher
 }
 
+type PreflightRule struct {
+	Name   string
+	Config map[string]any
+}
+
 func NewConfigFromResource(res ctlres.Resource) (Config, error) {
 	if res.APIVersion() != configAPIVersion {
 		return Config{}, fmt.Errorf(

pkg/kapp/permissions/preflight.go

@@ -37,6 +37,10 @@ func (p *Preflight) SetEnabled(enabled bool) {
 	p.enabled = enabled
 }
 
+func (p *Preflight) SetConfig(_ preflight.CheckConfig) error {
+	return nil
+}
+
 func (p *Preflight) Run(ctx context.Context, changeGraph *ctldgraph.ChangeGraph) error {
 	client, err := p.depsFactory.CoreClient()
 	if err != nil {

pkg/kapp/preflight/check.go

@@ -9,23 +9,30 @@ import (
 	ctldgraph "github.com/vmware-tanzu/carvel-kapp/pkg/kapp/diffgraph"
 )
 
-type CheckFunc func(context.Context, *ctldgraph.ChangeGraph) error
+type CheckFunc func(context.Context, *ctldgraph.ChangeGraph, CheckConfig) error
+type CheckConfig map[string]any
+type ConfigFunc func(CheckConfig) error
 
 type Check interface {
 	Enabled() bool
 	SetEnabled(bool)
+	SetConfig(CheckConfig) error
 	Run(context.Context, *ctldgraph.ChangeGraph) error
 }
 
 type checkImpl struct {
 	enabled   bool
 	checkFunc CheckFunc
+
+	config     CheckConfig
+	configFunc ConfigFunc
 }
 
-func NewCheck(cf CheckFunc, enabled bool) Check {
+func NewCheck(cf CheckFunc, sf ConfigFunc, enabled bool) Check {
 	return &checkImpl{
-		enabled:   enabled,
-		checkFunc: cf,
+		enabled:    enabled,
+		checkFunc:  cf,
+		configFunc: sf,
 	}
 }
 
@@ -37,6 +44,14 @@ func (cf *checkImpl) SetEnabled(enabled bool) {
 	cf.enabled = enabled
 }
 
+func (cf *checkImpl) SetConfig(config CheckConfig) error {
+	cf.config = config
+	if cf.configFunc != nil {
+		return cf.configFunc(config)
+	}
+	return nil
+}
+
 func (cf *checkImpl) Run(ctx context.Context, changeGraph *ctldgraph.ChangeGraph) error {
-	return cf.checkFunc(ctx, changeGraph)
+	return cf.checkFunc(ctx, changeGraph, cf.config)
 }

pkg/kapp/preflight/registry.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/spf13/pflag"
+	"github.com/vmware-tanzu/carvel-kapp/pkg/kapp/config"
 	ctldgraph "github.com/vmware-tanzu/carvel-kapp/pkg/kapp/diffgraph"
 )
 
@@ -17,6 +18,8 @@ const preflightFlag = "preflight"
 // Registry is a collection of preflight checks
 type Registry struct {
 	known map[string]Check
+	// Stores the enabled values from the command line
+	enabledFlag map[string]bool
 }
 
 // NewRegistry will return a new *Registry with the
@@ -59,25 +62,23 @@ func (c *Registry) Type() string {
 // Returns an error if there is a problem
 // parsing the preflight checks
 func (c *Registry) Set(s string) error {
-	if c.known == nil {
+	if c.known == nil || c.enabledFlag == nil {
 		return nil
 	}
 
-	enabled := map[string]struct{}{}
-	// enable those specified
+	// Using enabledFlag allows multiple --preflight check flags to be specified
 	mappings := strings.Split(s, ",")
 	for _, key := range mappings {
 		if _, ok := c.known[key]; !ok {
 			return fmt.Errorf("unknown preflight check %q specified", key)
 		}
-		c.known[key].SetEnabled(true)
-		enabled[key] = struct{}{}
+		c.enabledFlag[key] = true
 	}
-	// disable unspecified validators
+
+	// enable/disabled based on validators specified
 	for key := range c.known {
-		if _, ok := enabled[key]; !ok {
-			c.known[key].SetEnabled(false)
-		}
+		enabled, ok := c.enabledFlag[key]
+		c.known[key].SetEnabled(ok && enabled)
 	}
 	return nil
 }
@@ -101,9 +102,56 @@ func (c *Registry) AddCheck(name string, check Check) {
 	if c.known == nil {
 		c.known = make(map[string]Check)
 	}
+	if c.enabledFlag == nil {
+		c.enabledFlag = make(map[string]bool)
+	}
 	c.known[name] = check
 }
 
+// Validate the configuration provided; the rules are:
+// 1. Unknown validator = error
+// 2. Duplicate validator = error
+func (c *Registry) validateConfig(conf []config.PreflightRule) error {
+	haveConfig := map[string]bool{}
+	for _, rule := range conf {
+		if _, ok := c.known[rule.Name]; !ok {
+			return fmt.Errorf("unknown preflight check in configuration: %q", rule.Name)
+		}
+		if _, ok := haveConfig[rule.Name]; ok {
+			return fmt.Errorf("duplicate preflight check in configuration: %q", rule.Name)
+		}
+		haveConfig[rule.Name] = true
+	}
+	return nil
+}
+
+func (c *Registry) SetConfig(conf []config.PreflightRule) error {
+	// We get the --preflight cmdline flag _before_ the configuration from the file.
+	// So, we need to evaluate the config that we've gotten in light of the enabledFlag
+	if err := c.validateConfig(conf); err != nil {
+		return err
+	}
+	// map the configuration by name
+	config := map[string]map[string]any{}
+	for _, rule := range conf {
+		config[rule.Name] = rule.Config
+	}
+	if len(c.enabledFlag) == 0 {
+		// no --preflight flag, so enable validators according to their presence in the config
+		for name, check := range c.known {
+			_, ok := config[name]
+			check.SetEnabled(ok)
+		}
+	}
+	for name, check := range c.known {
+		err := check.SetConfig(config[name])
+		if err != nil {
+			return fmt.Errorf("setting preflight config %q: %w", name, err)
+		}
+	}
+	return nil
+}
+
 // Run will execute any enabled preflight checks. The provided
 // Context and ChangeGraph will be passed to the preflight checks
 // that are being executed.