healthcheck: monitor access to chain backend

Add a new health check package which will periodically poll health
check functions and shutdown if we do not succeed after our set number
of attempts. The first check that we add is one for our chain backend,
to ensure that we are connected to a bitcoin node.

config.go

@@ -86,6 +86,11 @@ const (
 	// HostAnnouncer will wait between DNS resolutions to check if the
 	// backing IP of a host has changed.
 	defaultHostSampleInterval = time.Minute * 5
+
+	defaultChainInterval = time.Minute
+	defaultChainTimeout  = time.Second * 10
+	defaultChainBackoff  = time.Second * 30
+	defaultChainAttempts = 3
 )
 
 var (
@@ -265,6 +270,8 @@ type Config struct {
 
 	AllowCircularRoute bool `long:"allow-circular-route" description:"If true, our node will allow htlc forwards that arrive and depart on the same channel."`
 
+	HealthChecks *lncfg.HealthCheckConfig `group:"healthcheck" namespace:"healthcheck"`
+
 	DB *lncfg.DB `group:"db" namespace:"db"`
 
 	// LogWriter is the root logger that all of the daemon's subloggers are
@@ -383,6 +390,14 @@ func DefaultConfig() Config {
 		Watchtower: &lncfg.Watchtower{
 			TowerDir: defaultTowerDir,
 		},
+		HealthChecks: &lncfg.HealthCheckConfig{
+			ChainCheck: &lncfg.CheckConfig{
+				Interval: defaultChainInterval,
+				Timeout:  defaultChainTimeout,
+				Attempts: defaultChainAttempts,
+				Backoff:  defaultChainBackoff,
+			},
+		},
 		MaxOutgoingCltvExpiry:   htlcswitch.DefaultMaxOutgoingCltvExpiry,
 		MaxChannelFeeAllocation: htlcswitch.DefaultMaxLinkFeeAllocation,
 		LogWriter:               build.NewRotatingLogWriter(),
@@ -1124,6 +1139,7 @@ func ValidateConfig(cfg Config, usageMessage string) (*Config, error) {
 		cfg.Caches,
 		cfg.WtClient,
 		cfg.DB,
+		cfg.HealthChecks,
 	)
 	if err != nil {
 		return nil, err