Add simple liveness endpoint

cmd/pqlogd/main.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/tls"
 	"flag"
+	"io"
 	"log"
 	"net"
 	"net/http"
@@ -47,6 +48,7 @@ func main() {
 
 	mux := http.NewServeMux()
 	mux.Handle("/metrics", promhttp.Handler())
+	mux.HandleFunc("/health", livenessHandler)
 
 	src, err := uri.Source()
 	if err != nil {
@@ -133,6 +135,10 @@ func buildListener() (net.Listener, error) {
 	return l, nil
 }
 
+func livenessHandler(w http.ResponseWriter, _ *http.Request) {
+	io.WriteString(w, "OK") // nolint:errcheck
+}
+
 // Instrumentation.
 func instrumentedHandler(h http.Handler, name string, withRequestSize bool) http.Handler {
 	labels := prometheus.Labels{"handler": name}