├── .gitignore ├── main.go ├── .travis.yml ├── strategy ├── first │ ├── first_config.go │ ├── first_config_test.go │ ├── first_test.go │ └── first.go └── random │ ├── random_test.go │ └── random.go ├── dns ├── api.go ├── dns_test.go └── lib.go ├── lb ├── config.go ├── generic_lb.go ├── roundrobin_test.go ├── lb.go ├── lb_test.go └── roundrobin.go ├── strategy_test.go ├── README.md └── LICENSE /.gitignore: -------------------------------------------------------------------------------- 1 | demo 2 | dns-clb 3 | -------------------------------------------------------------------------------- /main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | func main() { 4 | } 5 | -------------------------------------------------------------------------------- /.travis.yml: -------------------------------------------------------------------------------- 1 | language: go 2 | 3 | go: 4 | - 1.7 5 | - 1.8 6 | - 1.9 7 | - tip 8 | 9 | 10 | install: 11 | - go get -t ./... 12 | 13 | script: 14 | - go test ./... 15 | -------------------------------------------------------------------------------- /strategy/first/first_config.go: -------------------------------------------------------------------------------- 1 | package first 2 | 3 | import "github.com/benschw/srv-lb/lb" 4 | 5 | func Config() (*lb.Config, error) { 6 | config, err := lb.DefaultConfig() 7 | 8 | if err == nil { 9 | config.Strategy = FirstStrategy 10 | } 11 | 12 | return config, err 13 | } 14 | -------------------------------------------------------------------------------- /strategy/first/first_config_test.go: -------------------------------------------------------------------------------- 1 | package first 2 | 3 | import ( 4 | "testing" 5 | 6 | "github.com/stretchr/testify/assert" 7 | ) 8 | 9 | func TestFirstConfig(t *testing.T) { 10 | cfg, err := Config() 11 | 12 | assert.NoError(t, err) 13 | assert.Equal(t, FirstStrategy, cfg.Strategy, "should be equal") 14 | } 15 | -------------------------------------------------------------------------------- /dns/api.go: -------------------------------------------------------------------------------- 1 | package dns 2 | 3 | import ( 4 | "fmt" 5 | "net" 6 | ) 7 | 8 | type ByTarget []net.SRV 9 | 10 | func (a ByTarget) Len() int { return len(a) } 11 | func (a ByTarget) Swap(i, j int) { a[i], a[j] = a[j], a[i] } 12 | func (a ByTarget) Less(i, j int) bool { return a[i].Target < a[j].Target } 13 | 14 | type Address struct { 15 | Address string 16 | Port uint16 17 | } 18 | 19 | func (a Address) String() string { 20 | return fmt.Sprintf("%s:%d", a.Address, a.Port) 21 | } 22 | -------------------------------------------------------------------------------- /lb/config.go: -------------------------------------------------------------------------------- 1 | package lb 2 | 3 | import ( 4 | "os" 5 | 6 | "github.com/benschw/srv-lb/dns" 7 | ) 8 | 9 | type Config struct { 10 | Dns dns.Lookup 11 | Strategy StrategyType 12 | } 13 | 14 | func DefaultConfig() (*Config, error) { 15 | var dnsLib dns.Lookup 16 | 17 | if dnsHost := os.Getenv("SRVLB_HOST"); dnsHost != "" { 18 | dnsLib = dns.NewLookupLib(dnsHost) 19 | } else { 20 | lib, err := dns.NewDefaultLookupLib() 21 | if err != nil { 22 | return nil, err 23 | } 24 | dnsLib = lib 25 | } 26 | 27 | return &Config{ 28 | Dns: dnsLib, 29 | Strategy: RoundRobinStrategy, 30 | }, nil 31 | } 32 | -------------------------------------------------------------------------------- /strategy/first/first_test.go: -------------------------------------------------------------------------------- 1 | package first 2 | 3 | import ( 4 | "testing" 5 | 6 | "github.com/benschw/srv-lb/dns" 7 | "github.com/stretchr/testify/assert" 8 | ) 9 | 10 | func TestFirstLookup(t *testing.T) { 11 | lib, err := dns.NewDefaultLookupLib() 12 | assert.Nil(t, err) 13 | 14 | // given 15 | srvName := "foo.service.fligl.io" 16 | c := New(lib) 17 | 18 | // when 19 | address, err := c.Next(srvName) 20 | 21 | // then 22 | assert.Nil(t, err) 23 | 24 | if address.Port == 8001 && address.Address == "0.1.2.3" { 25 | return 26 | } else if address.Port == 8002 && address.Address == "4.5.6.7" { 27 | return 28 | } else { 29 | t.Errorf("port '%d' not expected with address: '%s'", address.Port, address.Address) 30 | } 31 | 32 | } 33 | -------------------------------------------------------------------------------- /strategy/first/first.go: -------------------------------------------------------------------------------- 1 | package first 2 | 3 | import ( 4 | "github.com/benschw/srv-lb/dns" 5 | "github.com/benschw/srv-lb/lb" 6 | ) 7 | 8 | const FirstStrategy lb.StrategyType = "first" 9 | 10 | func New(lib dns.Lookup) lb.GenericLoadBalancer { 11 | return &FirstClb{lib} 12 | } 13 | 14 | type FirstClb struct { 15 | dnsLib dns.Lookup 16 | } 17 | 18 | func (lb *FirstClb) Next(name string) (dns.Address, error) { 19 | var add dns.Address 20 | 21 | srvs, err := lb.dnsLib.LookupSRV(name) 22 | if err != nil { 23 | return add, err 24 | } 25 | 26 | ip, err := lb.dnsLib.LookupA(srvs[0].Target) 27 | if err != nil { 28 | return add, err 29 | } 30 | 31 | return dns.Address{Address: ip, Port: srvs[0].Port}, nil 32 | } 33 | 34 | func init() { 35 | lb.RegisterStrategy(FirstStrategy, New) 36 | } 37 | -------------------------------------------------------------------------------- /lb/generic_lb.go: -------------------------------------------------------------------------------- 1 | package lb 2 | 3 | import "github.com/benschw/srv-lb/dns" 4 | 5 | type StrategyType string 6 | type StrategyFactory func(dns.Lookup) GenericLoadBalancer 7 | 8 | var strategyReg map[StrategyType]StrategyFactory 9 | 10 | func RegisterStrategy(strategy StrategyType, factory StrategyFactory) { 11 | strategyReg[strategy] = factory 12 | } 13 | 14 | // Load balancer that can service request for any SRV record address 15 | type GenericLoadBalancer interface { 16 | Next(name string) (dns.Address, error) 17 | } 18 | 19 | func NewGeneric(cfg *Config) GenericLoadBalancer { 20 | if _, ok := strategyReg[cfg.Strategy]; !ok { 21 | panic("Unknown load balancer strategy") 22 | } 23 | return strategyReg[cfg.Strategy](cfg.Dns) 24 | } 25 | 26 | func init() { 27 | strategyReg = make(map[StrategyType]StrategyFactory) 28 | RegisterStrategy(RoundRobinStrategy, NewRoundRobinStrategy) 29 | } 30 | -------------------------------------------------------------------------------- /lb/roundrobin_test.go: -------------------------------------------------------------------------------- 1 | package lb 2 | 3 | import ( 4 | "fmt" 5 | "log" 6 | "testing" 7 | 8 | "github.com/benschw/srv-lb/dns" 9 | "github.com/stretchr/testify/assert" 10 | ) 11 | 12 | var _ = fmt.Print // For debugging; delete when done. 13 | var _ = log.Print // For debugging; delete when done. 14 | 15 | func TestRoundRobinLookup(t *testing.T) { 16 | lib, err := dns.NewDefaultLookupLib() 17 | assert.Nil(t, err) 18 | 19 | // given 20 | srvName := "foo.service.fligl.io" 21 | c := NewRoundRobinStrategy(lib) 22 | 23 | // when 24 | address, err := c.Next(srvName) 25 | 26 | // then 27 | assert.Nil(t, err) 28 | 29 | if address.Port == 8001 && address.Address == "0.1.2.3" { 30 | return 31 | } else if address.Port == 8002 && address.Address == "4.5.6.7" { 32 | return 33 | } else { 34 | t.Errorf("port '%d' not expected with address: '%s'", address.Port, address.Address) 35 | } 36 | 37 | } 38 | -------------------------------------------------------------------------------- /lb/lb.go: -------------------------------------------------------------------------------- 1 | package lb 2 | 3 | import "github.com/benschw/srv-lb/dns" 4 | 5 | // Load balancer that can service request for a configured SRV record address 6 | type LoadBalancer interface { 7 | Next() (dns.Address, error) 8 | } 9 | 10 | func New(cfg *Config, address string) LoadBalancer { 11 | return &SRVLoadBalancer{ 12 | Lb: NewGeneric(cfg), 13 | Address: address, 14 | } 15 | } 16 | 17 | // Default implementation for load balancing on a SRV record 18 | type SRVLoadBalancer struct { 19 | Lb GenericLoadBalancer 20 | Address string 21 | } 22 | 23 | func (s *SRVLoadBalancer) Next() (dns.Address, error) { 24 | return s.Lb.Next(s.Address) 25 | } 26 | 27 | // Specify an address to always return (good for compatibility and in test) 28 | type StaticLoadBalancer struct { 29 | Address dns.Address 30 | } 31 | 32 | func (s *StaticLoadBalancer) Next() (dns.Address, error) { 33 | return s.Address, nil 34 | } 35 | -------------------------------------------------------------------------------- /strategy/random/random_test.go: -------------------------------------------------------------------------------- 1 | package random 2 | 3 | import ( 4 | "fmt" 5 | "log" 6 | "testing" 7 | 8 | "github.com/benschw/srv-lb/dns" 9 | "github.com/stretchr/testify/assert" 10 | ) 11 | 12 | var _ = fmt.Print // For debugging; delete when done. 13 | var _ = log.Print // For debugging; delete when done. 14 | 15 | //strconv.FormatInt(int64(srv.Port), 10) 16 | func TestRandomLookup(t *testing.T) { 17 | lib, err := dns.NewDefaultLookupLib() 18 | assert.Nil(t, err) 19 | 20 | // given 21 | srvName := "foo.service.fligl.io" 22 | c := New(lib) 23 | 24 | // when 25 | address, err := c.Next(srvName) 26 | 27 | // then 28 | assert.Nil(t, err) 29 | 30 | if address.Port == 8001 && address.Address == "0.1.2.3" { 31 | return 32 | } else if address.Port == 8002 && address.Address == "4.5.6.7" { 33 | return 34 | } else { 35 | t.Errorf("port '%d' not expected with address: '%s'", address.Port, address.Address) 36 | } 37 | } 38 | -------------------------------------------------------------------------------- /strategy/random/random.go: -------------------------------------------------------------------------------- 1 | package random 2 | 3 | import ( 4 | "fmt" 5 | "math/rand" 6 | 7 | "github.com/benschw/srv-lb/dns" 8 | "github.com/benschw/srv-lb/lb" 9 | ) 10 | 11 | const RandomStrategy lb.StrategyType = "random" 12 | 13 | func New(lib dns.Lookup) lb.GenericLoadBalancer { 14 | lb := new(RandomClb) 15 | lb.dnsLib = lib 16 | return lb 17 | } 18 | 19 | type RandomClb struct { 20 | dnsLib dns.Lookup 21 | } 22 | 23 | func (lb *RandomClb) Next(name string) (dns.Address, error) { 24 | add := dns.Address{} 25 | 26 | srvs, err := lb.dnsLib.LookupSRV(name) 27 | if err != nil { 28 | return add, err 29 | } 30 | if len(srvs) == 0 { 31 | return add, fmt.Errorf("no SRV records found") 32 | } 33 | 34 | // log.Printf("%+v", srvs) 35 | srv := srvs[rand.Intn(len(srvs))] 36 | 37 | ip, err := lb.dnsLib.LookupA(srv.Target) 38 | if err != nil { 39 | return add, err 40 | } 41 | 42 | return dns.Address{Address: ip, Port: srv.Port}, nil 43 | } 44 | 45 | func init() { 46 | lb.RegisterStrategy(RandomStrategy, New) 47 | } 48 | -------------------------------------------------------------------------------- /lb/lb_test.go: -------------------------------------------------------------------------------- 1 | package lb 2 | 3 | import ( 4 | "fmt" 5 | "sort" 6 | 7 | "github.com/benschw/srv-lb/dns" 8 | ) 9 | 10 | type ByConnectionString []dns.Address 11 | 12 | func (a ByConnectionString) Len() int { return len(a) } 13 | func (a ByConnectionString) Swap(i, j int) { a[i], a[j] = a[j], a[i] } 14 | func (a ByConnectionString) Less(i, j int) bool { 15 | if a[i].Address == a[j].Address { 16 | return a[i].Port < a[j].Port 17 | } 18 | return a[i].Address < a[j].Address 19 | } 20 | 21 | // Example load balancer with defaults 22 | func ExampleNew() { 23 | cfg, err := DefaultConfig() 24 | if err != nil { 25 | panic(err) 26 | } 27 | lb := New(cfg, "foo.service.fligl.io") 28 | 29 | add1, err := lb.Next() 30 | if err != nil { 31 | panic(err) 32 | } 33 | add2, err := lb.Next() 34 | if err != nil { 35 | panic(err) 36 | } 37 | 38 | adds := []dns.Address{add1, add2} 39 | sort.Sort(ByConnectionString(adds)) 40 | 41 | fmt.Printf("%s\n%s", adds[0], adds[1]) 42 | // Output: 43 | // 0.1.2.3:8001 44 | // 4.5.6.7:8002 45 | } 46 | 47 | // Example of using a generic load balancer 48 | func ExampleNewGeneric() { 49 | srvName := "foo.service.fligl.io" 50 | cfg, err := DefaultConfig() 51 | if err != nil { 52 | panic(err) 53 | } 54 | lb := NewGeneric(cfg) 55 | 56 | add1, err := lb.Next(srvName) 57 | if err != nil { 58 | panic(err) 59 | } 60 | add2, err := lb.Next(srvName) 61 | if err != nil { 62 | panic(err) 63 | } 64 | 65 | adds := []dns.Address{add1, add2} 66 | sort.Sort(ByConnectionString(adds)) 67 | 68 | fmt.Printf("%s\n%s", adds[0], adds[1]) 69 | // Output: 70 | // 0.1.2.3:8001 71 | // 4.5.6.7:8002 72 | } 73 | -------------------------------------------------------------------------------- /strategy_test.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "sort" 5 | "testing" 6 | 7 | "github.com/benschw/srv-lb/dns" 8 | "github.com/benschw/srv-lb/lb" 9 | "github.com/benschw/srv-lb/strategy/first" 10 | "github.com/benschw/srv-lb/strategy/random" 11 | "github.com/stretchr/testify/assert" 12 | ) 13 | 14 | type ByConnectionString []dns.Address 15 | 16 | func (a ByConnectionString) Len() int { return len(a) } 17 | func (a ByConnectionString) Swap(i, j int) { a[i], a[j] = a[j], a[i] } 18 | func (a ByConnectionString) Less(i, j int) bool { 19 | if a[i].Address == a[j].Address { 20 | return a[i].Port < a[j].Port 21 | } 22 | return a[i].Address < a[j].Address 23 | } 24 | 25 | func TestRoundRobinStrategy(t *testing.T) { 26 | lib, err := dns.NewDefaultLookupLib() 27 | assert.Nil(t, err) 28 | 29 | //given 30 | c := lb.NewGeneric(&lb.Config{ 31 | Dns: lib, 32 | Strategy: lb.RoundRobinStrategy, 33 | }) 34 | 35 | // when 36 | srvName := "foo.service.fligl.io" 37 | add1, err1 := c.Next(srvName) 38 | add2, err2 := c.Next(srvName) 39 | 40 | // then 41 | assert.Nil(t, err1) 42 | assert.Nil(t, err2) 43 | 44 | adds := []dns.Address{add1, add2} 45 | sort.Sort(ByConnectionString(adds)) 46 | 47 | expected := []dns.Address{dns.Address{Address: "0.1.2.3", Port: 8001}, dns.Address{Address: "4.5.6.7", Port: 8002}} 48 | assert.Equal(t, expected, adds, "unexpected results") 49 | } 50 | 51 | func TestRandomStrategy(t *testing.T) { 52 | lib, err := dns.NewDefaultLookupLib() 53 | assert.Nil(t, err) 54 | 55 | //given 56 | c := lb.NewGeneric(&lb.Config{ 57 | Dns: lib, 58 | Strategy: random.RandomStrategy, 59 | }) 60 | 61 | // when 62 | srvName := "foo.service.fligl.io" 63 | _, err = c.Next(srvName) 64 | 65 | // then 66 | assert.Nil(t, err) 67 | } 68 | 69 | func TestFirstStrategy(t *testing.T) { 70 | lib, err := dns.NewDefaultLookupLib() 71 | assert.Nil(t, err) 72 | 73 | //given 74 | c := lb.NewGeneric(&lb.Config{ 75 | Dns: lib, 76 | Strategy: first.FirstStrategy, 77 | }) 78 | 79 | // when 80 | srvName := "foo.service.fligl.io" 81 | add1, err1 := c.Next(srvName) 82 | add2, err2 := c.Next(srvName) 83 | 84 | // then 85 | assert.Nil(t, err1) 86 | assert.Nil(t, err2) 87 | 88 | assert.NotEqual(t, add1, add2) 89 | } 90 | -------------------------------------------------------------------------------- /dns/dns_test.go: -------------------------------------------------------------------------------- 1 | package dns 2 | 3 | import ( 4 | "net" 5 | "sort" 6 | "testing" 7 | 8 | "github.com/miekg/dns" 9 | "github.com/stretchr/testify/assert" 10 | ) 11 | 12 | func TestLookupShouldFailWithBadNS(t *testing.T) { 13 | lib := NewLookupLib("foo:9999") 14 | 15 | _, err := lib.LookupA("foo") 16 | 17 | assert.NotNil(t, err) 18 | } 19 | 20 | func TestLookupShouldFailWithBadHost(t *testing.T) { 21 | lib := NewLookupLib("8.8.8.8:53") 22 | 23 | _, err := lib.LookupA("foo") 24 | 25 | assert.NotNil(t, err) 26 | } 27 | 28 | func TestLookupShouldResolveARecord(t *testing.T) { 29 | lib := NewLookupLib("8.8.8.8:53") 30 | 31 | address, err := lib.LookupA("github.com") 32 | 33 | assert.Nil(t, err) 34 | 35 | ip := net.ParseIP(address) 36 | assert.NotNil(t, ip.To4()) 37 | } 38 | 39 | func TestClientConfigLookupA(t *testing.T) { 40 | lib, err := NewClientConfigLookupLib(&predictableClientConfig{}) 41 | assert.Nil(t, err) 42 | 43 | address, err := lib.LookupA("github.com") 44 | 45 | assert.Nil(t, err) 46 | 47 | ip := net.ParseIP(address) 48 | assert.NotNil(t, ip.To4()) 49 | } 50 | 51 | func TestDefaultLookupSRV(t *testing.T) { 52 | lib, err := NewClientConfigLookupLib(&predictableClientConfig{}) 53 | assert.Nil(t, err) 54 | 55 | addresses, err := lib.LookupSRV("foo.service.fligl.io") 56 | 57 | assert.Nil(t, err) 58 | 59 | sort.Sort(ByTarget(addresses)) 60 | 61 | assert.Equal(t, 2, len(addresses), "should be two results") 62 | assert.Equal(t, "foo1.fligl.io.", addresses[0].Target, "Unexpected Result") 63 | assert.Equal(t, "foo2.fligl.io.", addresses[1].Target, "Unexpected Result") 64 | } 65 | 66 | func TestLookUpShouldSkipBadNS(t *testing.T) { 67 | lib, err := NewClientConfigLookupLib(&firstNSBadClientConfig{}) 68 | 69 | assert.Nil(t, err) 70 | 71 | address, err := lib.LookupA("github.com") 72 | 73 | assert.Nil(t, err) 74 | 75 | ip := net.ParseIP(address) 76 | assert.NotNil(t, ip.To4()) 77 | } 78 | 79 | type predictableClientConfig struct{} 80 | 81 | func (c *predictableClientConfig) Get() (*dns.ClientConfig, error) { 82 | return &dns.ClientConfig{ 83 | Servers: []string{"8.8.8.8", "8.8.4.4"}, 84 | Port: "53", 85 | }, nil 86 | } 87 | 88 | type firstNSBadClientConfig struct{} 89 | 90 | func (c *firstNSBadClientConfig) Get() (*dns.ClientConfig, error) { 91 | return &dns.ClientConfig{ 92 | Servers: []string{"foo", "8.8.8.8"}, 93 | Port: "53", 94 | }, nil 95 | } 96 | -------------------------------------------------------------------------------- /lb/roundrobin.go: -------------------------------------------------------------------------------- 1 | package lb 2 | 3 | import ( 4 | "fmt" 5 | "net" 6 | "sort" 7 | "sync" 8 | 9 | "github.com/benschw/srv-lb/dns" 10 | ) 11 | 12 | const RoundRobinStrategy StrategyType = "round-robin" 13 | 14 | func NewRoundRobinStrategy(lib dns.Lookup) GenericLoadBalancer { 15 | return &RoundRobinClb{ 16 | dnsLib: lib, 17 | cache: NewCache(), 18 | } 19 | } 20 | 21 | type RoundRobinClb struct { 22 | dnsLib dns.Lookup 23 | cache *ResultCache 24 | } 25 | 26 | func (lb *RoundRobinClb) Next(name string) (dns.Address, error) { 27 | var add dns.Address 28 | 29 | srvs, err := lb.dnsLib.LookupSRV(name) 30 | if err != nil { 31 | return add, err 32 | } 33 | 34 | srv, err := lb.cache.Next(name, srvs) 35 | if err != nil { 36 | return add, err 37 | } 38 | 39 | ip, err := lb.dnsLib.LookupA(srv.Target) 40 | if err != nil { 41 | return add, err 42 | } 43 | 44 | return dns.Address{Address: ip, Port: srv.Port}, nil 45 | } 46 | 47 | type AddressResult struct { 48 | srvs []net.SRV 49 | i int 50 | } 51 | 52 | type ResultCache struct { 53 | m map[string]*AddressResult 54 | sync.RWMutex 55 | } 56 | 57 | func NewCache() *ResultCache { 58 | return &ResultCache{ 59 | m: make(map[string]*AddressResult), 60 | } 61 | } 62 | 63 | func (s *ResultCache) Next(key string, srvs []net.SRV) (net.SRV, error) { 64 | s.Lock() 65 | defer s.Unlock() 66 | 67 | s.applyResults(key, srvs) 68 | 69 | return s.getNextResult(key) 70 | } 71 | 72 | func (s *ResultCache) applyResults(key string, srvs []net.SRV) { 73 | old, ok := s.m[key] 74 | if !ok { 75 | old = &AddressResult{ 76 | srvs: make([]net.SRV, 0), 77 | i: 0, 78 | } 79 | s.m[key] = old 80 | } 81 | ordered, changed := s.mergeResults(old.srvs, srvs) 82 | if changed { 83 | s.m[key].srvs = ordered 84 | s.m[key].i = 0 85 | } 86 | } 87 | 88 | func (s *ResultCache) mergeResults(oldResults []net.SRV, newResults []net.SRV) ([]net.SRV, bool) { 89 | sort.Sort(dns.ByTarget(newResults)) 90 | 91 | if len(oldResults) != len(newResults) { 92 | return newResults, true 93 | } 94 | 95 | for i, val := range oldResults { 96 | if newResults[i] != val { 97 | return newResults, true 98 | } 99 | } 100 | 101 | return newResults, false 102 | } 103 | 104 | func (s *ResultCache) getNextResult(key string) (net.SRV, error) { 105 | var srv net.SRV 106 | 107 | srvs := s.m[key].srvs 108 | i := s.m[key].i 109 | 110 | if len(srvs) == 0 { 111 | return srv, fmt.Errorf("no results found for '%s'", key) 112 | } 113 | 114 | if len(srvs) <= i { 115 | i = i % len(srvs) 116 | } 117 | 118 | srv = srvs[i] 119 | s.m[key].i = i + 1 120 | 121 | return srv, nil 122 | } 123 | -------------------------------------------------------------------------------- /dns/lib.go: -------------------------------------------------------------------------------- 1 | package dns 2 | 3 | import ( 4 | "errors" 5 | "fmt" 6 | "net" 7 | 8 | "github.com/miekg/dns" 9 | ) 10 | 11 | type Lookup interface { 12 | LookupSRV(name string) ([]net.SRV, error) 13 | LookupA(name string) (string, error) 14 | } 15 | 16 | type ClientConfig interface { 17 | Get() (*dns.ClientConfig, error) 18 | } 19 | 20 | type ResolvConfClientConfig struct { 21 | File string 22 | } 23 | 24 | func (f *ResolvConfClientConfig) Get() (*dns.ClientConfig, error) { 25 | return dns.ClientConfigFromFile(f.File) 26 | } 27 | 28 | func NewDefaultLookupLib() (Lookup, error) { 29 | return NewClientConfigLookupLib(&ResolvConfClientConfig{"/etc/resolv.conf"}) 30 | } 31 | 32 | func NewClientConfigLookupLib(cfg ClientConfig) (Lookup, error) { 33 | config, err := cfg.Get() 34 | if err != nil { 35 | return nil, err 36 | } 37 | l := new(lookupLib) 38 | l.servers = make([]string, len(config.Servers)) 39 | for i, s := range config.Servers { 40 | l.servers[i] = s + ":" + config.Port 41 | } 42 | return l, nil 43 | } 44 | 45 | func NewLookupLib(serverString string) Lookup { 46 | l := new(lookupLib) 47 | l.servers = []string{serverString} 48 | return l 49 | } 50 | 51 | type lookupLib struct { 52 | servers []string 53 | } 54 | 55 | func (l *lookupLib) LookupSRV(name string) ([]net.SRV, error) { 56 | var srvs = make([]net.SRV, 0) 57 | answer, err := l.lookupType(name, "SRV") 58 | if err != nil { 59 | return srvs, err 60 | } 61 | return l.parseSRVAnswer(answer) 62 | } 63 | 64 | func (l *lookupLib) LookupA(name string) (string, error) { 65 | answer, err := l.lookupType(name, "A") 66 | if err != nil { 67 | return "", err 68 | } 69 | return l.parseAAnswer(answer) 70 | } 71 | 72 | func (l *lookupLib) parseSRVAnswer(answer *dns.Msg) ([]net.SRV, error) { 73 | var srvs = make([]net.SRV, 0) 74 | for _, v := range answer.Answer { 75 | if srv, ok := v.(*dns.SRV); ok { 76 | srvs = append(srvs, net.SRV{ 77 | Priority: srv.Priority, 78 | Weight: srv.Weight, 79 | Port: srv.Port, 80 | Target: srv.Target, 81 | }) 82 | } 83 | } 84 | return srvs, nil 85 | } 86 | 87 | func (l *lookupLib) parseAAnswer(answer *dns.Msg) (string, error) { 88 | if len(answer.Answer) == 0 { 89 | return "", fmt.Errorf("Answer Empty") 90 | } 91 | if a, ok := answer.Answer[0].(*dns.A); ok { 92 | 93 | return a.A.String(), nil 94 | 95 | // return string(a.A[:n]), nil 96 | } 97 | return "", fmt.Errorf("Could not parse A record") 98 | } 99 | 100 | func (l *lookupLib) lookupType(name string, recordType string) (*dns.Msg, error) { 101 | if len(l.servers) < 1 { 102 | return nil, errors.New("No DNS servers configured") 103 | } 104 | 105 | var err error 106 | for _, s := range l.servers { 107 | // try a connection with a udp connection first 108 | var msg *dns.Msg 109 | msg, err = lookup(s, name, recordType, "") 110 | if err == nil { 111 | return msg, nil 112 | } 113 | } 114 | // Returns the last error we encountered. 115 | return nil, err 116 | } 117 | 118 | func lookup(server, name string, recordType string, connType string) (*dns.Msg, error) { 119 | qType, ok := dns.StringToType[recordType] 120 | if !ok { 121 | return nil, fmt.Errorf("Invalid type '%s'", recordType) 122 | } 123 | name = dns.Fqdn(name) 124 | 125 | client := &dns.Client{Net: connType} 126 | 127 | msg := &dns.Msg{} 128 | msg.SetQuestion(name, qType) 129 | 130 | response, _, err := client.Exchange(msg, server) 131 | 132 | if err != nil { 133 | if connType == "" { 134 | // retry lookup with a tcp connection 135 | return lookup(server, name, recordType, "tcp") 136 | } else { 137 | return nil, fmt.Errorf("Couldn't resolve name '%s'", name) 138 | } 139 | } 140 | 141 | if msg.Id != response.Id { 142 | return nil, fmt.Errorf("DNS ID mismatch, request: %d, response: %d", msg.Id, response.Id) 143 | } 144 | 145 | return response, nil 146 | } 147 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | [![Build Status](https://travis-ci.org/benschw/srv-lb.svg?branch=master)](https://travis-ci.org/benschw/srv-lb) 2 | [![GoDoc](http://godoc.org/github.com/benschw/srv-lb?status.png)](http://godoc.org/github.com/benschw/srv-lb/lb) 3 | 4 | 5 | # SRV Record Load Balancer library for Go 6 | 7 | _SRV-LB_ is a load balancer library designed for use with service discovery solutions 8 | that expose an interface through DNS SRV records 9 | (e.g. [consul](https://consul.io/) or [skyDNS](https://github.com/skynetservices/skydns)) 10 | 11 | 12 | The library selects a `SRV` record answer according to specified load balancer algorithm, 13 | resolves its `A` record to an ip, and returns an `Address` structure: 14 | 15 | type Address struct { 16 | Address string 17 | Port uint16 18 | } 19 | 20 | 21 | To select a DNS server you can use the value from your system's `resolv.conf` (the default), 22 | specify it explicitly when configuring the library, 23 | or set it as an ENV variable (e.g. `SRVLB_HOST=127.0.0.1:8600` to connect to a local consul agent) at run time. 24 | 25 | 26 | The library defaults to use a "Round Robin" algorithm, but you can specify another or build your own (see below). 27 | 28 | 29 | ## Example: 30 | ### Default Load Balancer 31 | 32 | srvName := "foo.service.fligl.io" 33 | cfg, err := lb.DefaultConfig() 34 | if err != nil { 35 | panic(err) 36 | } 37 | 38 | l := lb.New(cfg, srvName) 39 | 40 | address, err := l.Next() 41 | if err != nil { 42 | panic(err) 43 | } 44 | 45 | fmt.Printf("%s", address.String()) 46 | // Output: 0.1.2.3:8001 47 | 48 | - Uses dns server configured in `/etc/resolv.conf` 49 | - Uses round robin strategy 50 | 51 | 52 | ### or build a generic load balancer 53 | 54 | srvName := "foo.service.fligl.io" 55 | cfg, err := lb.DefaultConfig() 56 | if err != nil { 57 | panic(err) 58 | } 59 | 60 | l := lb.NewGeneric(cfg) 61 | 62 | address, err := l.Next(srvName) 63 | if err != nil { 64 | panic(err) 65 | } 66 | 67 | fmt.Printf("%s", address.String()) 68 | // Output: 0.1.2.3:8001 69 | 70 | ### or configure explicitly 71 | 72 | srvName := "foo.service.fligl.io" 73 | cfg := &lb.Config{ 74 | Dns: dns.NewLookupLib("127.0.0.1:8600"), 75 | Strategy: random.RandomStrategy, 76 | } 77 | l := lb.New(cfg, srvName) 78 | 79 | address, err := l.Next() 80 | if err != nil { 81 | panic(err) 82 | } 83 | 84 | fmt.Printf("%s", address.String()) 85 | // Output: 0.1.2.3:8001 86 | 87 | 88 | 89 | ## Development 90 | tests are run against some fixture dns entries I set up on fligl.io (`dig foo.service.fligl.io SRV`). 91 | 92 | go get -u -t ./... 93 | go test ./... 94 | 95 | 96 | ## Build your own load balancing strategy 97 | 98 | `srv-lb` leverages go's `init()` function to allow you to use your own 99 | load balancer strategy without forking the core library. Below is a walkthrough 100 | of how to create your own "FancyLB" strategy. For a complete example, 101 | [see how the "random" strategy is implemented](https://github.com/benschw/srv-lb/blob/master/strategy/random/random.go). 102 | 103 | Of course, if your strategy would be generally usefull I would lolve a pull request! 104 | 105 | _The default strategy, `RoundRobin`, is registered slightly differently to avoid import cycles, so avoid using it as an example_ 106 | 107 | 108 | Give your strategy a unique identifier 109 | 110 | const FancyStrategy lb.StrategyType = "fancy" 111 | 112 | Create a factory (and your implementation of `GenericLoadBalancer`) 113 | 114 | func New(lib dns.Lookup) lb.GenericLoadBalancer { 115 | return &FancyLB{Dns: lib} 116 | } 117 | 118 | Register it with the load balancer 119 | 120 | func init() { 121 | lb.RegisterStrategy(FancyStrategy, New) 122 | } 123 | 124 | 125 | And then specify it when constructing your load balancer 126 | 127 | cfg, _ := lb.DefaultConfig() 128 | cfg.Strategy = fancy.FancyStrategy 129 | 130 | l := lb.New(cfg, srvName) 131 | 132 | 133 | ## Projects Using SRV-LB 134 | 135 | - [chinchilla](https://github.com/benschw/chinchilla) - a rabbitmq to REST bridge 136 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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You may not convey a covered 525 | work if you are a party to an arrangement with a third party that is 526 | in the business of distributing software, under which you make payment 527 | to the third party based on the extent of your activity of conveying 528 | the work, and under which the third party grants, to any of the 529 | parties who would receive the covered work from you, a discriminatory 530 | patent license (a) in connection with copies of the covered work 531 | conveyed by you (or copies made from those copies), or (b) primarily 532 | for and in connection with specific products or compilations that 533 | contain the covered work, unless you entered into that arrangement, 534 | or that patent license was granted, prior to 28 March 2007. 535 | 536 | Nothing in this License shall be construed as excluding or limiting 537 | any implied license or other defenses to infringement that may 538 | otherwise be available to you under applicable patent law. 539 | 540 | 12. No Surrender of Others' Freedom. 541 | 542 | If conditions are imposed on you (whether by court order, agreement or 543 | otherwise) that contradict the conditions of this License, they do not 544 | excuse you from the conditions of this License. If you cannot convey a 545 | covered work so as to satisfy simultaneously your obligations under this 546 | License and any other pertinent obligations, then as a consequence you may 547 | not convey it at all. For example, if you agree to terms that obligate you 548 | to collect a royalty for further conveying from those to whom you convey 549 | the Program, the only way you could satisfy both those terms and this 550 | License would be to refrain entirely from conveying the Program. 551 | 552 | 13. Use with the GNU Affero General Public License. 553 | 554 | Notwithstanding any other provision of this License, you have 555 | permission to link or combine any covered work with a work licensed 556 | under version 3 of the GNU Affero General Public License into a single 557 | combined work, and to convey the resulting work. The terms of this 558 | License will continue to apply to the part which is the covered work, 559 | but the special requirements of the GNU Affero General Public License, 560 | section 13, concerning interaction through a network will apply to the 561 | combination as such. 562 | 563 | 14. Revised Versions of this License. 564 | 565 | The Free Software Foundation may publish revised and/or new versions of 566 | the GNU General Public License from time to time. Such new versions will 567 | be similar in spirit to the present version, but may differ in detail to 568 | address new problems or concerns. 569 | 570 | Each version is given a distinguishing version number. If the 571 | Program specifies that a certain numbered version of the GNU General 572 | Public License "or any later version" applies to it, you have the 573 | option of following the terms and conditions either of that numbered 574 | version or of any later version published by the Free Software 575 | Foundation. If the Program does not specify a version number of the 576 | GNU General Public License, you may choose any version ever published 577 | by the Free Software Foundation. 578 | 579 | If the Program specifies that a proxy can decide which future 580 | versions of the GNU General Public License can be used, that proxy's 581 | public statement of acceptance of a version permanently authorizes you 582 | to choose that version for the Program. 583 | 584 | Later license versions may give you additional or different 585 | permissions. However, no additional obligations are imposed on any 586 | author or copyright holder as a result of your choosing to follow a 587 | later version. 588 | 589 | 15. Disclaimer of Warranty. 590 | 591 | THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY 592 | APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT 593 | HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY 594 | OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, 595 | THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 596 | PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM 597 | IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF 598 | ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 599 | 600 | 16. Limitation of Liability. 601 | 602 | IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 603 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 604 | THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 605 | GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 606 | USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 607 | DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 608 | PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 609 | EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 610 | SUCH DAMAGES. 611 | 612 | 17. Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | --------------------------------------------------------------------------------