add option to register service alias for fabio

This patch adds an "alias" option which tells Fabio to register a new
frontend service in Consul on behalf of the requesting backend service.
The new service provides Consul-hosted A records to Fabio with the
desired service name.

main.go

@@ -106,7 +106,7 @@ func main() {
 		if registry.Default == nil {
 			return
 		}
-		registry.Default.Deregister()
+		registry.Default.Deregister("")
 	})
 
 	// init metrics early since that create the global metric registries
@@ -284,6 +284,7 @@ func startServers(cfg *config.Config) {
 					ConnFail:    metrics.DefaultRegistry.GetCounter("tcp_sni.connfail"),
 					Noroute:     metrics.DefaultRegistry.GetCounter("tcp_sni.noroute"),
 				}
+
 				if err := proxy.ListenAndServeTCP(l, h, tlscfg); err != nil {
 					exit.Fatal("[FATAL] ", err)
 				}
@@ -354,7 +355,7 @@ func initBackend(cfg *config.Config) {
 		}
 
 		if err == nil {
-			if err = registry.Default.Register(); err == nil {
+			if err = registry.Default.Register(""); err == nil {
 				return
 			}
 		}
@@ -396,6 +397,8 @@ func watchBackend(cfg *config.Config, first chan bool) {
 			continue
 		}
 
+		registry.Default.UpdateAliases(next)
+
 		t, err := route.NewTable(next)
 		if err != nil {
 			log.Printf("[WARN] %s", err)

registry/backend.go

@@ -2,10 +2,13 @@ package registry
 
 type Backend interface {
 	// Register registers fabio as a service in the registry.
-	Register() error
+	Register(serviceName string) error
 
 	// Deregister removes the service registration for fabio.
-	Deregister() error
+	Deregister(serviceName string) error
+
+	// UpdateAliases() is used to add new aliases and remove obsolete aliases
+	UpdateAliases(config string) error
 
 	// ReadManual returns the current manual overrides and
 	// their version as seen by the registry.

registry/consul/backend.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/fabiolb/fabio/config"
 	"github.com/fabiolb/fabio/registry"
+	"github.com/fabiolb/fabio/route"
 
 	"github.com/hashicorp/consul/api"
 )
@@ -15,7 +16,7 @@ type be struct {
 	c     *api.Client
 	dc    string
 	cfg   *config.Consul
-	dereg chan bool
+	dereg map[string](chan bool)
 }
 
 func NewBackend(cfg *config.Consul) (registry.Backend, error) {
@@ -36,26 +37,47 @@ func NewBackend(cfg *config.Consul) (registry.Backend, error) {
 	return &be{c: c, dc: dc, cfg: cfg}, nil
 }
 
-func (b *be) Register() error {
-	if !b.cfg.Register {
+func (b *be) Register(serviceName string) error {
+	if len(serviceName) == 0 {
+		serviceName = b.cfg.ServiceName
+	}
+
+	if serviceName == b.cfg.ServiceName && !b.cfg.Register {
 		log.Printf("[INFO] consul: Not registering fabio in consul")
 		return nil
 	}
 
-	service, err := serviceRegistration(b.cfg)
+	service, err := serviceRegistration(b.cfg, serviceName)
 	if err != nil {
 		return err
 	}
 
-	b.dereg = register(b.c, service)
+	if b.dereg == nil {
+		b.dereg = make(map[string](chan bool))
+	}
+
+	b.dereg[serviceName] = register(b.c, service)
+
 	return nil
 }
 
-func (b *be) Deregister() error {
-	if b.dereg != nil {
-		b.dereg <- true // trigger deregistration
-		<-b.dereg       // wait for completion
+func (b *be) Deregister(serviceName string) error {
+	if len(serviceName) == 0 {
+		for name, dereg := range b.dereg {
+			if dereg != nil {
+				log.Printf("[INFO]: consul: Deregistering %q", name)
+				dereg <- true // trigger deregistration
+				<-dereg       // wait for completion
+			}
+		}
+	} else {
+		if dereg := b.dereg[serviceName]; dereg != nil {
+			dereg <- true
+			<-dereg
+			delete(b.dereg, serviceName)
+		}
 	}
+
 	return nil
 }
 
@@ -100,6 +122,54 @@ func (b *be) WatchNoRouteHTML() chan string {
 	return html
 }
 
+func (b *be) UpdateAliases(config string) error {
+	defs, err := route.Parse(config)
+	if err != nil {
+		return err
+	}
+
+	var aliases []string
+
+	if b.cfg.Register {
+		aliases = append(aliases, b.cfg.ServiceName)
+	}
+
+	for _, d := range defs {
+		if d.Opts["alias"] != "" {
+			log.Printf("[DEBUG]: consul: Service %q wants alias %q", d.Service, d.Opts["alias"])
+			aliases = append(aliases, d.Opts["alias"])
+		}
+	}
+
+	// register new aliases
+	for _, alias := range aliases {
+		if _, hasAlias := b.dereg[alias]; hasAlias {
+			log.Printf("[DEBUG]: consul: Skipping registration for existing alias %q", alias)
+			continue
+		}
+		log.Printf("[DEBUG]: consul: Registering new alias %q", alias)
+		err := registry.Default.Register(alias)
+		if err != nil {
+			log.Printf("[WARN] %q", err)
+		}
+	}
+
+	// deregister old aliases
+	for alias := range b.dereg {
+		if stringInSlice(alias, aliases) {
+			log.Printf("[DEBUG]: consul: Keeping alias %q", alias)
+			continue
+		}
+		log.Printf("[DEBUG]: consul: Deregister alias %q", alias)
+		err := registry.Default.Deregister(alias)
+		if err != nil {
+			log.Printf("[WARN] %s", err)
+		}
+	}
+
+	return nil
+}
+
 // datacenter returns the datacenter of the local agent
 func datacenter(c *api.Client) (string, error) {
 	self, err := c.Agent().Self()
@@ -117,3 +187,12 @@ func datacenter(c *api.Client) (string, error) {
 	}
 	return dc, nil
 }
+
+func stringInSlice(str string, strSlice []string) bool {
+	for _, s := range strSlice {
+		if s == str {
+			return true
+		}
+	}
+	return false
+}

registry/consul/register.go

@@ -38,10 +38,11 @@ func register(c *api.Client, service *api.AgentServiceRegistration) chan bool {
 
 	register := func() string {
 		if err := c.Agent().ServiceRegister(service); err != nil {
-			log.Printf("[ERROR] consul: Cannot register fabio in consul. %s", err)
+			log.Printf("[ERROR] consul: Cannot register fabio [name:%q] in Consul. %s", service.Name, err)
 			return ""
 		}
 
+		log.Printf("[INFO] consul: Registered fabio with name %q", service.Name)
 		log.Printf("[INFO] consul: Registered fabio with id %q", service.ID)
 		log.Printf("[INFO] consul: Registered fabio with address %q", service.Address)
 		log.Printf("[INFO] consul: Registered fabio with tags %q", strings.Join(service.Tags, ","))
@@ -51,7 +52,7 @@ func register(c *api.Client, service *api.AgentServiceRegistration) chan bool {
 	}
 
 	deregister := func(serviceID string) {
-		log.Printf("[INFO] consul: Deregistering fabio")
+		log.Printf("[INFO] consul: Deregistering %s", service.Name)
 		c.Agent().ServiceDeregister(serviceID)
 	}
 
@@ -76,7 +77,7 @@ func register(c *api.Client, service *api.AgentServiceRegistration) chan bool {
 	return dereg
 }
 
-func serviceRegistration(cfg *config.Consul) (*api.AgentServiceRegistration, error) {
+func serviceRegistration(cfg *config.Consul, serviceName string) (*api.AgentServiceRegistration, error) {
 	hostname, err := os.Hostname()
 	if err != nil {
 		return nil, err
@@ -101,7 +102,7 @@ func serviceRegistration(cfg *config.Consul) (*api.AgentServiceRegistration, err
 		}
 	}
 
-	serviceID := fmt.Sprintf("%s-%s-%d", cfg.ServiceName, hostname, port)
+	serviceID := fmt.Sprintf("%s-%s-%d", serviceName, hostname, port)
 
 	checkURL := fmt.Sprintf("%s://%s:%d/health", cfg.CheckScheme, ip, port)
 	if ip.To16() != nil {
@@ -110,7 +111,7 @@ func serviceRegistration(cfg *config.Consul) (*api.AgentServiceRegistration, err
 
 	service := &api.AgentServiceRegistration{
 		ID:      serviceID,
-		Name:    cfg.ServiceName,
+		Name:    serviceName,
 		Address: ip.String(),
 		Port:    port,
 		Tags:    cfg.ServiceTags,

registry/static/backend.go

@@ -15,11 +15,15 @@ func NewBackend(cfg *config.Static) (registry.Backend, error) {
 	return &be{cfg}, nil
 }
 
-func (b *be) Register() error {
+func (b *be) Register(serviceName string) error {
 	return nil
 }
 
-func (b *be) Deregister() error {
+func (b *be) Deregister(serviceName string) error {
+	return nil
+}
+
+func (b *be) UpdateAliases(config string) error {
 	return nil
 }