feat: implement control plane loadbalancer

A simple wrapper around generic TCP loadbalancer which implements
control plane loadbalancer.

Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>

controlplane/controlplane.go

@@ -0,0 +1,113 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// Package controlplane wraps generic TCP loadbalancer for Kubernetes controlplane endpoint LB.
+package controlplane
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"strconv"
+	"time"
+
+	"github.com/talos-systems/go-loadbalancer/loadbalancer"
+)
+
+// LoadBalancer provides Kubernetes control plane TCP loadbalancer with a way to update endpoints (list of control plane nodes).
+type LoadBalancer struct {
+	lb loadbalancer.TCP
+
+	done chan struct{}
+
+	endpoint string
+}
+
+// NewLoadBalancer initializes the load balancer.
+//
+// If bindPort is zero, load balancer will bind to a random available port.
+func NewLoadBalancer(bindAddress string, bindPort int, logWriter io.Writer) (*LoadBalancer, error) {
+	if bindPort == 0 {
+		var err error
+
+		bindPort, err = findListenPort(bindAddress)
+		if err != nil {
+			return nil, fmt.Errorf("unable to find available port: %w", err)
+		}
+	}
+
+	lb := &LoadBalancer{
+		endpoint: net.JoinHostPort(bindAddress, strconv.Itoa(bindPort)),
+	}
+
+	// set aggressive timeouts to prevent proxying to unhealthy upstreams
+	lb.lb.DialTimeout = 5 * time.Second
+	lb.lb.KeepAlivePeriod = time.Second
+	lb.lb.TCPUserTimeout = 5 * time.Second
+
+	lb.lb.Logger = log.New(logWriter, lb.endpoint+" ", log.Default().Flags())
+
+	// create a route without any upstreams yet
+	if err := lb.lb.AddRoute(lb.endpoint, nil); err != nil {
+		return nil, err
+	}
+
+	return lb, nil
+}
+
+// Endpoint returns loadbalancer endpoint as "host:port".
+func (lb *LoadBalancer) Endpoint() string {
+	return lb.endpoint
+}
+
+// Start the loadbalancer providing a channel which provides endpoint list update.
+//
+// Load balancer starts with an empty list of endpoints, so initial list should be provided on the channel.
+func (lb *LoadBalancer) Start(upstreamCh <-chan []string) error {
+	if err := lb.lb.Start(); err != nil {
+		return err
+	}
+
+	lb.done = make(chan struct{})
+
+	go func() {
+		for {
+			select {
+			case upstreams := <-upstreamCh:
+				if err := lb.lb.ReconcileRoute(lb.endpoint, upstreams); err != nil {
+					lb.lb.Logger.Printf("failed reconciling list of upstreams: %s", err)
+				}
+			case <-lb.done:
+				return
+			}
+		}
+	}()
+
+	return nil
+}
+
+// Shutdown the loadbalancer listener and wait for the connections to be closed.
+func (lb *LoadBalancer) Shutdown() error {
+	if err := lb.lb.Close(); err != nil {
+		return err
+	}
+
+	close(lb.done)
+
+	lb.lb.Wait() //nolint:errcheck
+
+	return nil
+}
+
+func findListenPort(address string) (int, error) {
+	l, err := net.Listen("tcp", net.JoinHostPort(address, "0"))
+	if err != nil {
+		return 0, err
+	}
+
+	port := l.Addr().(*net.TCPAddr).Port //nolint:forcetypeassert
+
+	return port, l.Close()
+}

controlplane/controlplane_test.go

@@ -0,0 +1,141 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package controlplane_test
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net"
+	"os"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/talos-systems/go-retry/retry"
+	"go.uber.org/goleak"
+
+	"github.com/talos-systems/go-loadbalancer/controlplane"
+)
+
+type mockUpstream struct {
+	addr string
+	l    net.Listener
+
+	identity string
+}
+
+func (u *mockUpstream) Start() error {
+	var err error
+
+	u.l, err = net.Listen("tcp", "localhost:0")
+	if err != nil {
+		return err
+	}
+
+	u.addr = u.l.Addr().String()
+
+	go u.serve()
+
+	return nil
+}
+
+func (u *mockUpstream) serve() {
+	for {
+		c, err := u.l.Accept()
+		if err != nil {
+			return
+		}
+
+		c.Write([]byte(u.identity)) //nolint: errcheck
+		c.Close()                   //nolint: errcheck
+	}
+}
+
+func (u *mockUpstream) Close() {
+	u.l.Close() //nolint: errcheck
+}
+
+func TestLoadBalancer(t *testing.T) {
+	defer goleak.VerifyNone(t, goleak.IgnoreCurrent())
+
+	const (
+		upstreamCount = 5
+		pivot         = 2
+	)
+
+	upstreams := make([]mockUpstream, upstreamCount)
+	for i := range upstreams {
+		upstreams[i].identity = strconv.Itoa(i)
+		require.NoError(t, upstreams[i].Start())
+	}
+
+	upstreamAddrs := make([]string, len(upstreams))
+	for i := range upstreamAddrs {
+		upstreamAddrs[i] = upstreams[i].addr
+	}
+
+	lb, err := controlplane.NewLoadBalancer("localhost", 0, os.Stderr)
+	require.NoError(t, err)
+
+	upstreamCh := make(chan []string)
+
+	require.NoError(t, lb.Start(upstreamCh))
+
+	upstreamCh <- upstreamAddrs[:pivot]
+
+	readIdentity := func() (int, error) {
+		c, err := net.Dial("tcp", lb.Endpoint())
+		if err != nil {
+			return 0, retry.ExpectedError(err)
+		}
+
+		defer c.Close() //nolint:errcheck
+
+		id, err := ioutil.ReadAll(c)
+		if err != nil {
+			return 0, retry.ExpectedError(err)
+		}
+
+		return strconv.Atoi(string(id))
+	}
+
+	assert.NoError(t, retry.Constant(10*time.Second, retry.WithUnits(time.Second)).Retry(func() error {
+		identity, err := readIdentity()
+		if err != nil {
+			return err
+		}
+
+		if identity < 0 || identity > pivot-1 {
+			return fmt.Errorf("unexpected response: %d", identity)
+		}
+
+		return nil
+	}))
+
+	// change the upstreams
+	upstreamCh <- upstreamAddrs[pivot:]
+
+	assert.NoError(t, retry.Constant(10*time.Second, retry.WithUnits(time.Second)).Retry(func() error {
+		identity, err := readIdentity()
+		if err != nil {
+			return err
+		}
+
+		// upstreams are not changed immediately, there might be some stale responses
+		if identity < pivot {
+			return retry.ExpectedErrorf("unexpected response: %d", identity)
+		}
+
+		return nil
+	}))
+
+	assert.NoError(t, lb.Shutdown())
+
+	for i := range upstreams {
+		upstreams[i].Close()
+	}
+}