Merge pull request #528 from milosgajdos83/router

Adds router package

router/default_router.go

@@ -0,0 +1,316 @@
+package router
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/micro/go-micro/registry"
+	"github.com/olekukonko/tablewriter"
+)
+
+var (
+	// AdvertiseTick defines how often in seconds do we scal the local registry
+	// to advertise the local services to the network registry
+	AdvertiseTick = 5 * time.Second
+	// AdvertiseTTL defines network registry TTL in seconds
+	// NOTE: this is a rather arbitrary picked value subject to change
+	AdvertiseTTL = 120 * time.Second
+)
+
+type router struct {
+	opts Options
+	exit chan struct{}
+	wg   *sync.WaitGroup
+}
+
+// newRouter creates new router and returns it
+func newRouter(opts ...Option) Router {
+	// get default options
+	options := DefaultOptions()
+
+	// apply requested options
+	for _, o := range opts {
+		o(&options)
+	}
+
+	return &router{
+		opts: options,
+		exit: make(chan struct{}),
+		wg:   &sync.WaitGroup{},
+	}
+}
+
+// Init initializes router with given options
+func (r *router) Init(opts ...Option) error {
+	for _, o := range opts {
+		o(&r.opts)
+	}
+	return nil
+}
+
+// Options returns router options
+func (r *router) Options() Options {
+	return r.opts
+}
+
+// ID returns router ID
+func (r *router) ID() string {
+	return r.opts.ID
+}
+
+// Table returns routing table
+func (r *router) Table() Table {
+	return r.opts.Table
+}
+
+// Address returns router's bind address
+func (r *router) Address() string {
+	return r.opts.Address
+}
+
+// Network returns the address router advertises to the network
+func (r *router) Network() string {
+	return r.opts.Advertise
+}
+
+// Start starts the router
+func (r *router) Start() error {
+	// add local service routes into the routing table
+	if err := r.addServiceRoutes(r.opts.Registry, DefaultLocalMetric); err != nil {
+		return fmt.Errorf("failed adding routes for local services: %v", err)
+	}
+
+	// add network service routes into the routing table
+	if err := r.addServiceRoutes(r.opts.Network, DefaultNetworkMetric); err != nil {
+		return fmt.Errorf("failed adding routes for network services: %v", err)
+	}
+
+	node, err := r.parseToNode()
+	if err != nil {
+		return fmt.Errorf("failed to parse router into service node: %v", err)
+	}
+
+	localWatcher, err := r.opts.Registry.Watch()
+	if err != nil {
+		return fmt.Errorf("failed to create local registry watcher: %v", err)
+	}
+
+	networkWatcher, err := r.opts.Network.Watch()
+	if err != nil {
+		return fmt.Errorf("failed to create network registry watcher: %v", err)
+	}
+
+	// error channel collecting goroutine errors
+	errChan := make(chan error, 3)
+
+	r.wg.Add(1)
+	go func() {
+		defer r.wg.Done()
+		// watch local registry and register routes in routine table
+		errChan <- r.manageServiceRoutes(localWatcher, DefaultLocalMetric)
+	}()
+
+	r.wg.Add(1)
+	go func() {
+		defer r.wg.Done()
+		// watch network registry and register routes in routine table
+		errChan <- r.manageServiceRoutes(networkWatcher, DefaultNetworkMetric)
+	}()
+
+	r.wg.Add(1)
+	go func() {
+		defer r.wg.Done()
+		// watch local registry and advertise local service to the network
+		errChan <- r.advertiseToNetwork(node)
+	}()
+
+	return <-errChan
+}
+
+// addServiceRouteslists all available services in given registry and adds them to the routing table.
+// NOTE: this is a one-off operation done when bootstrapping the routing table of the new router.
+// It returns error if either the services could not be listed or if the routes could not be added to the routing table.
+func (r *router) addServiceRoutes(reg registry.Registry, metric int) error {
+	services, err := reg.ListServices()
+	if err != nil {
+		return fmt.Errorf("failed to list services: %v", err)
+	}
+
+	for _, service := range services {
+		route := Route{
+			Destination: service.Name,
+			Router:      r,
+			Network:     r.opts.Advertise,
+			Metric:      metric,
+		}
+		if err := r.opts.Table.Add(route); err != nil && err != ErrDuplicateRoute {
+			return fmt.Errorf("error adding route for service: %s", service.Name)
+		}
+	}
+
+	return nil
+}
+
+// parseToNode parses router into registry.Node and returns the result.
+// It returns error if the router network address could not be parsed into host and port.
+// NOTE: We use ":" as the delimiter when we splitting the router network address.
+func (r *router) parseToNode() (*registry.Node, error) {
+	// split on ":" as a standard host/port delimiter
+	addr := strings.Split(r.opts.Advertise, ":")
+	// try to parse network port into integer
+	port, err := strconv.Atoi(addr[1])
+	if err != nil {
+		return nil, fmt.Errorf("could not parse router network address: %v", err)
+	}
+
+	node := &registry.Node{
+		Id:      r.opts.ID,
+		Address: addr[0],
+		Port:    port,
+	}
+
+	return node, nil
+}
+
+// advertiseToNetwork periodically scans local registry and registers (i.e. advertises) all the local services in the network registry.
+// It returns error if either the local services failed to be listed or if it fails to register local service in network registry.
+func (r *router) advertiseToNetwork(node *registry.Node) error {
+	// ticker to periodically scan the local registry
+	ticker := time.NewTicker(AdvertiseTick)
+
+	for {
+		select {
+		case <-r.exit:
+			return nil
+		case <-ticker.C:
+			// list all local services
+			services, err := r.opts.Registry.ListServices()
+			if err != nil {
+				return fmt.Errorf("failed to list local services: %v", err)
+			}
+			// loop through all registered local services and register them in the network registry
+			for _, service := range services {
+				svc := &registry.Service{
+					Name:  service.Name,
+					Nodes: []*registry.Node{node},
+				}
+				// register the local service in the network registry
+				if err := r.opts.Network.Register(svc, registry.RegisterTTL(AdvertiseTTL)); err != nil {
+					return fmt.Errorf("failed to register service %s in network registry: %v", svc.Name, err)
+				}
+			}
+		}
+	}
+}
+
+// manageServiceRoutes watches services in given registry and updates the routing table accordingly.
+// It returns error if the service registry watcher has stopped or if the routing table failed to be updated.
+func (r *router) manageServiceRoutes(w registry.Watcher, metric int) error {
+	// wait in the background for the router to stop
+	// when the router stops, stop the watcher and exit
+	r.wg.Add(1)
+	go func() {
+		defer r.wg.Done()
+		<-r.exit
+		w.Stop()
+	}()
+
+	var watchErr error
+
+	for {
+		res, err := w.Next()
+		if err == registry.ErrWatcherStopped {
+			break
+		}
+
+		if err != nil {
+			watchErr = err
+			break
+		}
+
+		route := Route{
+			Destination: res.Service.Name,
+			Router:      r,
+			Network:     r.opts.Advertise,
+			Metric:      metric,
+		}
+
+		switch res.Action {
+		case "create":
+			if len(res.Service.Nodes) > 0 {
+				// only return error if the route is not duplicate, but something else has failed
+				if err := r.opts.Table.Add(route); err != nil && err != ErrDuplicateRoute {
+					return fmt.Errorf("failed to add route for service: %v", res.Service.Name)
+				}
+			}
+		case "delete":
+			if len(res.Service.Nodes) < 1 {
+				// only return error if the route is present in the table, but something else has failed
+				if err := r.opts.Table.Delete(route); err != nil && err != ErrRouteNotFound {
+					return fmt.Errorf("failed to delete route for service: %v", res.Service.Name)
+				}
+			}
+		}
+	}
+
+	return watchErr
+}
+
+// Stop stops the router
+func (r *router) Stop() error {
+	// notify all goroutines to finish
+	close(r.exit)
+
+	// wait for all goroutines to finish
+	r.wg.Wait()
+
+	// NOTE: we need a more efficient way of doing this e.g. network routes
+	// should ideally be autodeleted when the router stops gossiping
+	query := NewQuery(QueryRouter(r), QueryNetwork(r.opts.Advertise))
+	routes, err := r.opts.Table.Lookup(query)
+	if err != nil && err != ErrRouteNotFound {
+		return fmt.Errorf("failed to lookup routes for router %s: %v", r.opts.ID, err)
+	}
+
+	// parse router to registry.Node
+	node, err := r.parseToNode()
+	if err != nil {
+		return fmt.Errorf("failed to parse router into service node: %v", err)
+	}
+
+	for _, route := range routes {
+		service := &registry.Service{
+			Name:  route.Destination,
+			Nodes: []*registry.Node{node},
+		}
+		if err := r.opts.Network.Deregister(service); err != nil {
+			return fmt.Errorf("failed to deregister service %s from network registry: %v", service.Name, err)
+		}
+	}
+
+	return nil
+}
+
+// String prints debugging information about router
+func (r *router) String() string {
+	sb := &strings.Builder{}
+
+	table := tablewriter.NewWriter(sb)
+	table.SetHeader([]string{"ID", "Address", "Network", "Table"})
+
+	data := []string{
+		r.opts.ID,
+		r.opts.Address,
+		r.opts.Advertise,
+		fmt.Sprintf("%d", r.opts.Table.Size()),
+	}
+	table.Append(data)
+
+	// render table into sb
+	table.Render()
+
+	return sb.String()
+}

router/default_table.go

@@ -0,0 +1,289 @@
+package router
+
+import (
+	"fmt"
+	"hash"
+	"hash/fnv"
+	"strings"
+	"sync"
+
+	"github.com/google/uuid"
+	"github.com/olekukonko/tablewriter"
+)
+
+// TableOptions are routing table options
+// TODO: table options TBD in the future
+type TableOptions struct{}
+
+// table is in memory routing table
+type table struct {
+	// opts are table options
+	opts TableOptions
+	// m stores routing table map
+	m map[string]map[uint64]Route
+	// h hashes route entries
+	h hash.Hash64
+	// w is a list of table watchers
+	w map[string]*tableWatcher
+	sync.RWMutex
+}
+
+// newTable creates in memory routing table and returns it
+func newTable(opts ...TableOption) Table {
+	// default options
+	var options TableOptions
+
+	// apply requested options
+	for _, o := range opts {
+		o(&options)
+	}
+
+	h := fnv.New64()
+	h.Reset()
+
+	return &table{
+		opts: options,
+		m:    make(map[string]map[uint64]Route),
+		w:    make(map[string]*tableWatcher),
+		h:    h,
+	}
+}
+
+// Init initializes routing table with options
+func (t *table) Init(opts ...TableOption) error {
+	for _, o := range opts {
+		o(&t.opts)
+	}
+	return nil
+}
+
+// Options returns routing table options
+func (t *table) Options() TableOptions {
+	return t.opts
+}
+
+// Add adds a route to the routing table
+func (t *table) Add(r Route) error {
+	destAddr := r.Destination
+	sum := t.hash(r)
+
+	t.Lock()
+	defer t.Unlock()
+
+	// check if the destination has any routes in the table
+	if _, ok := t.m[destAddr]; !ok {
+		t.m[destAddr] = make(map[uint64]Route)
+		t.m[destAddr][sum] = r
+		go t.sendEvent(&Event{Type: CreateEvent, Route: r})
+		return nil
+	}
+
+	// add new route to the table for the given destination
+	if _, ok := t.m[destAddr][sum]; !ok {
+		t.m[destAddr][sum] = r
+		go t.sendEvent(&Event{Type: CreateEvent, Route: r})
+		return nil
+	}
+
+	// only add the route if the route override is explicitly requested
+	if _, ok := t.m[destAddr][sum]; ok && r.Policy == OverrideIfExists {
+		t.m[destAddr][sum] = r
+		go t.sendEvent(&Event{Type: UpdateEvent, Route: r})
+		return nil
+	}
+
+	// if we reached this point without already returning the route already exists
+	// we return nil only if explicitly requested by the client
+	if r.Policy == IgnoreIfExists {
+		return nil
+	}
+
+	return ErrDuplicateRoute
+}
+
+// Delete deletes the route from the routing table
+func (t *table) Delete(r Route) error {
+	t.Lock()
+	defer t.Unlock()
+
+	destAddr := r.Destination
+	sum := t.hash(r)
+
+	if _, ok := t.m[destAddr]; !ok {
+		return ErrRouteNotFound
+	}
+
+	delete(t.m[destAddr], sum)
+	go t.sendEvent(&Event{Type: DeleteEvent, Route: r})
+
+	return nil
+}
+
+// Update updates routing table with new route
+func (t *table) Update(r Route) error {
+	destAddr := r.Destination
+	sum := t.hash(r)
+
+	t.Lock()
+	defer t.Unlock()
+
+	// check if the destAddr has ANY routes in the table
+	if _, ok := t.m[destAddr]; !ok {
+		return ErrRouteNotFound
+	}
+
+	// if the route has been found update it
+	if _, ok := t.m[destAddr][sum]; ok {
+		t.m[destAddr][sum] = r
+		go t.sendEvent(&Event{Type: UpdateEvent, Route: r})
+		return nil
+	}
+
+	return ErrRouteNotFound
+}
+
+// List returns a list of all routes in the table
+func (t *table) List() ([]Route, error) {
+	t.RLock()
+	defer t.RUnlock()
+
+	var routes []Route
+	for _, rmap := range t.m {
+		for _, route := range rmap {
+			routes = append(routes, route)
+		}
+	}
+
+	return routes, nil
+}
+
+// Lookup queries routing table and returns all routes that match it
+func (t *table) Lookup(q Query) ([]Route, error) {
+	t.RLock()
+	defer t.RUnlock()
+
+	var results []Route
+
+	for destAddr, routes := range t.m {
+		if q.Options().Destination != "*" {
+			if q.Options().Destination != destAddr {
+				continue
+			}
+			for _, route := range routes {
+				if q.Options().Network == "*" || q.Options().Network == route.Network {
+					if q.Options().Router.ID() == "*" || q.Options().Router.ID() == route.Router.ID() {
+						if route.Metric <= q.Options().Metric {
+							results = append(results, route)
+						}
+					}
+				}
+			}
+		}
+
+		if q.Options().Destination == "*" {
+			for _, route := range routes {
+				if q.Options().Network == "*" || q.Options().Network == route.Router.Network() {
+					if q.Options().Router.ID() == "*" || q.Options().Router.ID() == route.Router.ID() {
+						if route.Metric <= q.Options().Metric {
+							results = append(results, route)
+						}
+					}
+				}
+			}
+		}
+	}
+
+	if len(results) == 0 && q.Options().Policy != DiscardNoRoute {
+		return nil, ErrRouteNotFound
+	}
+
+	return results, nil
+}
+
+// Watch returns routing table entry watcher
+func (t *table) Watch(opts ...WatchOption) (Watcher, error) {
+	// by default watch everything
+	wopts := WatchOptions{
+		Destination: "*",
+		Network:     "*",
+	}
+
+	for _, o := range opts {
+		o(&wopts)
+	}
+
+	watcher := &tableWatcher{
+		opts:    wopts,
+		resChan: make(chan *Event, 10),
+		done:    make(chan struct{}),
+	}
+
+	t.Lock()
+	t.w[uuid.New().String()] = watcher
+	t.Unlock()
+
+	return watcher, nil
+}
+
+// sendEvent sends rules to all subscribe watchers
+func (t *table) sendEvent(r *Event) {
+	t.RLock()
+	defer t.RUnlock()
+
+	for _, w := range t.w {
+		select {
+		case w.resChan <- r:
+		case <-w.done:
+		}
+	}
+}
+
+// Size returns the size of the routing table
+func (t *table) Size() int {
+	t.RLock()
+	defer t.RUnlock()
+
+	return len(t.m)
+}
+
+// String returns debug information
+func (t *table) String() string {
+	t.RLock()
+	defer t.RUnlock()
+
+	// this will help us build routing table string
+	sb := &strings.Builder{}
+
+	// create nice table printing structure
+	table := tablewriter.NewWriter(sb)
+	table.SetHeader([]string{"Destination", "Router", "Network", "Metric"})
+
+	for _, destRoute := range t.m {
+		for _, route := range destRoute {
+			strRoute := []string{
+				route.Destination,
+				route.Router.Address(),
+				route.Network,
+				fmt.Sprintf("%d", route.Metric),
+			}
+			table.Append(strRoute)
+		}
+	}
+
+	// render table into sb
+	table.Render()
+
+	return sb.String()
+}
+
+// hash hashes the route using router gateway and network address
+func (t *table) hash(r Route) uint64 {
+	destAddr := r.Destination
+	routerAddr := r.Router.Address()
+	netAddr := r.Network
+
+	t.h.Reset()
+	t.h.Write([]byte(destAddr + routerAddr + netAddr))
+
+	return t.h.Sum64()
+}

router/options.go

@@ -0,0 +1,84 @@
+package router
+
+import (
+	"github.com/google/uuid"
+	"github.com/micro/go-micro/registry"
+)
+
+var (
+	// DefaultAddress is default router address
+	DefaultAddress = ":9093"
+	// DefaultAdvertise is default address advertised to the network
+	DefaultAdvertise = ":9094"
+)
+
+// Options are router options
+type Options struct {
+	// ID is router id
+	ID string
+	// Address is router address
+	Address string
+	// Advertise is the address advertised to the network
+	Advertise string
+	// Registry is the local registry
+	Registry registry.Registry
+	// Networkis the network registry
+	Network registry.Registry
+	// Table is routing table
+	Table Table
+}
+
+// ID sets Router ID
+func ID(id string) Option {
+	return func(o *Options) {
+		o.ID = id
+	}
+}
+
+// Address sets router service address
+func Address(a string) Option {
+	return func(o *Options) {
+		o.Address = a
+	}
+}
+
+// Advertise sets the address that is advertise to the network
+func Advertise(n string) Option {
+	return func(o *Options) {
+		o.Advertise = n
+	}
+}
+
+// RoutingTable sets the routing table
+func RoutingTable(t Table) Option {
+	return func(o *Options) {
+		o.Table = t
+	}
+}
+
+// Registry sets the local registry
+func Registry(r registry.Registry) Option {
+	return func(o *Options) {
+		o.Registry = r
+	}
+}
+
+// Network sets the network registry
+func Network(r registry.Registry) Option {
+	return func(o *Options) {
+		o.Network = r
+	}
+}
+
+// DefaultOptions returns router default options
+func DefaultOptions() Options {
+	// NOTE: by default both local and network registies use default registry i.e. mdns
+	return Options{
+		ID:        uuid.New().String(),
+		Address:   DefaultAddress,
+		Advertise: DefaultAdvertise,
+		Registry:  registry.DefaultRegistry,
+		Network:   registry.DefaultRegistry,
+		Table:     NewTable(),
+	}
+}

router/query.go

@@ -0,0 +1,116 @@
+package router
+
+// LookupPolicy defines query policy
+type LookupPolicy int
+
+const (
+	// DiscardNoRoute discards query when no route is found
+	DiscardNoRoute LookupPolicy = iota
+	// ClosestMatch returns closest match to supplied query
+	ClosestMatch
+)
+
+// String returns human representation of LookupPolicy
+func (lp LookupPolicy) String() string {
+	switch lp {
+	case DiscardNoRoute:
+		return "DISCARD"
+	case ClosestMatch:
+		return "CLOSEST"
+	default:
+		return "UNKNOWN"
+	}
+}
+
+// QueryOption sets routing table query options
+type QueryOption func(*QueryOptions)
+
+// QueryOptions are routing table query options
+type QueryOptions struct {
+	// Destination is destination address
+	Destination string
+	// Network is network address
+	Network string
+	// Router is gateway address
+	Router Router
+	// Metric is route metric
+	Metric int
+	// Policy is query lookup policy
+	Policy LookupPolicy
+}
+
+// QueryDestination sets query destination address
+func QueryDestination(a string) QueryOption {
+	return func(o *QueryOptions) {
+		o.Destination = a
+	}
+}
+
+// QueryNetwork sets query network address
+func QueryNetwork(a string) QueryOption {
+	return func(o *QueryOptions) {
+		o.Network = a
+	}
+}
+
+// QueryRouter sets query gateway address
+func QueryRouter(r Router) QueryOption {
+	return func(o *QueryOptions) {
+		o.Router = r
+	}
+}
+
+// QueryMetric sets query metric
+func QueryMetric(m int) QueryOption {
+	return func(o *QueryOptions) {
+		o.Metric = m
+	}
+}
+
+// QueryPolicy sets query policy
+// NOTE: this might be renamed to filter or some such
+func QueryPolicy(p LookupPolicy) QueryOption {
+	return func(o *QueryOptions) {
+		o.Policy = p
+	}
+}
+
+// Query is routing table query
+type Query interface {
+	// Options returns query options
+	Options() QueryOptions
+}
+
+// query is a basic implementation of Query
+type query struct {
+	opts QueryOptions
+}
+
+// NewQuery creates new query and returns it
+func NewQuery(opts ...QueryOption) Query {
+	// default gateway for wildcard router
+	r := newRouter(ID("*"))
+
+	// default options
+	// NOTE: by default we use DefaultNetworkMetric
+	qopts := QueryOptions{
+		Destination: "*",
+		Network:     "*",
+		Router:      r,
+		Metric:      DefaultNetworkMetric,
+		Policy:      DiscardNoRoute,
+	}
+
+	for _, o := range opts {
+		o(&qopts)
+	}
+
+	return &query{
+		opts: qopts,
+	}
+}
+
+// Options returns query options
+func (q *query) Options() QueryOptions {
+	return q.opts
+}

router/route.go

@@ -0,0 +1,74 @@
+package router
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/olekukonko/tablewriter"
+)
+
+var (
+	// DefaultLocalMetric is default route cost for local network
+	DefaultLocalMetric = 1
+	// DefaultNetworkMetric is default route cost for micro network
+	DefaultNetworkMetric = 10
+)
+
+// RoutePolicy defines routing table addition policy
+type RoutePolicy int
+
+const (
+	// OverrideIfExists overrides route if it already exists
+	OverrideIfExists RoutePolicy = iota
+	// IgnoreIfExists does not modify existing route
+	IgnoreIfExists
+)
+
+// String returns human reprensentation of policy
+func (p RoutePolicy) String() string {
+	switch p {
+	case OverrideIfExists:
+		return "OVERRIDE"
+	case IgnoreIfExists:
+		return "IGNORE"
+	default:
+		return "UNKNOWN"
+	}
+}
+
+// Route is network route
+type Route struct {
+	// Destination is destination address
+	Destination string
+	// Router is the network router
+	Router Router
+	// Network is micro network address
+	Network string
+	// Metric is the route cost metric
+	Metric int
+	// Policy defines route policy
+	Policy RoutePolicy
+}
+
+// String allows to print the route
+func (r *Route) String() string {
+	// this will help us build routing table string
+	sb := &strings.Builder{}
+
+	// create nice table printing structure
+	table := tablewriter.NewWriter(sb)
+	table.SetHeader([]string{"Destination", "Router", "Network", "Metric"})
+
+	strRoute := []string{
+		r.Destination,
+		r.Router.Address(),
+		r.Network,
+		fmt.Sprintf("%d", r.Metric),
+	}
+	table.Append(strRoute)
+
+	// render table into sb
+	table.Render()
+
+	return sb.String()
+}

router/router.go

@@ -0,0 +1,32 @@
+// Package router provides an interface for micro network router
+package router
+
+// Router is micro network router
+type Router interface {
+	// Init initializes the router with options
+	Init(...Option) error
+	// Options returns the router options
+	Options() Options
+	// ID returns id of the router
+	ID() string
+	// Table returns the router routing table
+	Table() Table
+	// Address returns the router adddress
+	Address() string
+	// Network returns the router network address
+	Network() string
+	// Start starts the router
+	Start() error
+	// Stop stops the router
+	Stop() error
+	// String returns debug info
+	String() string
+}
+
+// Option used by the router
+type Option func(*Options)
+
+// NewRouter creates new Router and returns it
+func NewRouter(opts ...Option) Router {
+	return newRouter(opts...)
+}

router/table.go

@@ -0,0 +1,44 @@
+package router
+
+import (
+	"errors"
+)
+
+var (
+	// ErrRouteNotFound is returned when no route was found in the routing table
+	ErrRouteNotFound = errors.New("route not found")
+	// ErrDuplicateRoute is returned when the route already exists
+	ErrDuplicateRoute = errors.New("duplicate route")
+)
+
+// Table defines routing table interface
+type Table interface {
+	// Init initializes the router with options
+	Init(...TableOption) error
+	// Options returns the router options
+	Options() TableOptions
+	// Add adds new route to the routing table
+	Add(Route) error
+	// Delete deletes existing route from the routing table
+	Delete(Route) error
+	// Update updates route in the routing table
+	Update(Route) error
+	// List returns the list of all routes in the table
+	List() ([]Route, error)
+	// Lookup looks up routes in the routing table and returns them
+	Lookup(Query) ([]Route, error)
+	// Watch returns a watcher which allows to track updates to the routing table
+	Watch(opts ...WatchOption) (Watcher, error)
+	// Size returns the size of the routing table
+	Size() int
+	// String prints the routing table
+	String() string
+}
+
+// TableOption used by the routing table
+type TableOption func(*TableOptions)
+
+// NewTable creates new routing table and returns it
+func NewTable(opts ...TableOption) Table {
+	return newTable(opts...)
+}

router/table_watcher.go

@@ -0,0 +1,147 @@
+package router
+
+import (
+	"errors"
+	"strings"
+
+	"github.com/olekukonko/tablewriter"
+)
+
+var (
+	// ErrWatcherStopped is returned when routing table watcher has been stopped
+	ErrWatcherStopped = errors.New("routing table watcher stopped")
+)
+
+// EventType defines routing table event
+type EventType int
+
+const (
+	// CreateEvent is emitted when new route has been created
+	CreateEvent EventType = iota
+	// DeleteEvent is emitted when an existing route has been deleted
+	DeleteEvent
+	// UpdateEvent is emitted when a routing table has been updated
+	UpdateEvent
+)
+
+// String returns string representation of the event
+func (et EventType) String() string {
+	switch et {
+	case CreateEvent:
+		return "CREATE"
+	case DeleteEvent:
+		return "DELETE"
+	case UpdateEvent:
+		return "UPDATE"
+	default:
+		return "UNKNOWN"
+	}
+}
+
+// Event is returned by a call to Next on the watcher.
+type Event struct {
+	// Type defines type of event
+	Type EventType
+	// Route is table rout
+	Route Route
+}
+
+// WatchOption is used to define what routes to watch in the table
+type WatchOption func(*WatchOptions)
+
+// Watcher defines routing table watcher interface
+// Watcher returns updates to the routing table
+type Watcher interface {
+	// Next is a blocking call that returns watch result
+	Next() (*Event, error)
+	// Chan returns event channel
+	Chan() (<-chan *Event, error)
+	// Stop stops watcher
+	Stop()
+}
+
+// WatchOptions are table watcher options
+type WatchOptions struct {
+	// Specify destination address to watch
+	Destination string
+	// Specify network to watch
+	Network string
+}
+
+// WatchDestination sets what destination to watch
+// Destination is usually microservice name
+func WatchDestination(a string) WatchOption {
+	return func(o *WatchOptions) {
+		o.Destination = a
+	}
+}
+
+// WatchNetwork sets what network to watch
+func WatchNetwork(n string) WatchOption {
+	return func(o *WatchOptions) {
+		o.Network = n
+	}
+}
+
+type tableWatcher struct {
+	opts    WatchOptions
+	resChan chan *Event
+	done    chan struct{}
+}
+
+// Next returns the next noticed action taken on table
+// TODO: this needs to be thought through properly
+// we are aiming to provide the same options Query provides
+func (w *tableWatcher) Next() (*Event, error) {
+	for {
+		select {
+		case res := <-w.resChan:
+			switch w.opts.Destination {
+			case "*", "":
+				if w.opts.Network == "*" || w.opts.Network == res.Route.Network {
+					return res, nil
+				}
+			case res.Route.Destination:
+				if w.opts.Network == "*" || w.opts.Network == res.Route.Network {
+					return res, nil
+				}
+			}
+		case <-w.done:
+			return nil, ErrWatcherStopped
+		}
+	}
+}
+
+// Chan returns watcher events channel
+func (w *tableWatcher) Chan() (<-chan *Event, error) {
+	return w.resChan, nil
+}
+
+// Stop stops routing table watcher
+func (w *tableWatcher) Stop() {
+	select {
+	case <-w.done:
+		return
+	default:
+		close(w.done)
+	}
+}
+
+// String prints debug information
+func (w *tableWatcher) String() string {
+	sb := &strings.Builder{}
+
+	table := tablewriter.NewWriter(sb)
+	table.SetHeader([]string{"Destination", "Network"})
+
+	data := []string{
+		w.opts.Destination,
+		w.opts.Network,
+	}
+	table.Append(data)
+
+	// render table into sb
+	table.Render()
+
+	return sb.String()
+}