external-dns/source/wrappers/post_processor.go

/*
Copyright 2025 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package wrappers

import (
	"context"
	"strings"
	"time"

	log "github.com/sirupsen/logrus"

	"sigs.k8s.io/external-dns/endpoint"
	"sigs.k8s.io/external-dns/source"
	"sigs.k8s.io/external-dns/source/annotations"
)

type postProcessor struct {
	source source.Source
	cfg    PostProcessorConfig
}

type PostProcessorConfig struct {
	ttl          int64
	provider     string
	preferAlias  bool
	isConfigured bool
}

type PostProcessorOption func(*PostProcessorConfig)

func WithTTL(ttl time.Duration) PostProcessorOption {
	return func(cfg *PostProcessorConfig) {
		if int64(ttl.Seconds()) > 0 {
			cfg.isConfigured = true
			cfg.ttl = int64(ttl.Seconds())
		}
	}
}

// WithPostProcessorProvider sets the provider used to retain provider-specific
// properties on endpoints. Empty or whitespace-only values are ignored.
func WithPostProcessorProvider(input string) PostProcessorOption {
	return func(cfg *PostProcessorConfig) {
		if p := strings.TrimSpace(input); p != "" {
			cfg.isConfigured = true
			cfg.provider = p
		}
	}
}

// WithPostProcessorPreferAlias enables setting alias=true on CNAME endpoints.
// This signals to providers that support ALIAS records (like PowerDNS, AWS)
// to create ALIAS records instead of CNAMEs.
func WithPostProcessorPreferAlias(enabled bool) PostProcessorOption {
	return func(cfg *PostProcessorConfig) {
		cfg.preferAlias = enabled
		if enabled {
			cfg.isConfigured = true
		}
	}
}

func NewPostProcessor(source source.Source, opts ...PostProcessorOption) source.Source {
	cfg := PostProcessorConfig{}
	for _, opt := range opts {
		opt(&cfg)
	}
	return &postProcessor{source: source, cfg: cfg}
}

func (pp *postProcessor) Endpoints(ctx context.Context) ([]*endpoint.Endpoint, error) {
	endpoints, err := pp.source.Endpoints(ctx)
	if err != nil {
		return nil, err
	}

	if !pp.cfg.isConfigured {
		return endpoints, nil
	}

	for _, ep := range endpoints {
		if ep == nil {
			continue
		}
		ep.WithMinTTL(pp.cfg.ttl)
		ep.RetainProviderProperties(pp.cfg.provider)
		// Set alias annotation for CNAME records when preferAlias is enabled
		// Only set if not already explicitly configured at the source level
		if pp.cfg.preferAlias && ep.RecordType == endpoint.RecordTypeCNAME {
			if _, exists := ep.GetProviderSpecificProperty(annotations.AliasKey); !exists {
				ep.WithProviderSpecific("alias", "true")
			}
		}
	}

	return endpoints, nil
}

func (pp *postProcessor) AddEventHandler(ctx context.Context, handler func()) {
	log.Debug("postProcessor: adding event handler")
	pp.source.AddEventHandler(ctx, handler)
}