add health check endpoint

Author: ezekg

README.md

@@ -166,6 +166,16 @@ relay serve --port 8080 --ttl 30s --strategy fifo
 The API can be consumed by the vendor's application to claim and release a
 license on behalf of a node.
 
+#### Health Check
+
+The Relay server's health can be tested with the following endpoint:
+
+```bash
+curl -v -X GET "http://localhost:6349/v1/health"
+```
+
+Returns a `200 OK` status code.
+
 #### Claim license
 
 Nodes can claim a license by sending a `PUT` request to the

internal/server/handler.go

@@ -2,10 +2,11 @@ package server
 
 import (
 	"encoding/json"
-	"github.com/gorilla/mux"
-	"github.com/keygen-sh/keygen-relay/internal/licenses"
 	"log/slog"
 	"net/http"
+
+	"github.com/gorilla/mux"
+	"github.com/keygen-sh/keygen-relay/internal/licenses"
 )
 
 type RequestBodyPayload struct {
@@ -33,10 +34,15 @@ func NewHandler(m licenses.Manager) Handler {
 }
 
 func (h *handler) RegisterRoutes(r *mux.Router) {
+	r.HandleFunc("/v1/health", h.HealthCheck).Methods("GET")
 	r.HandleFunc("/v1/nodes/{fingerprint}", h.ClaimLicense).Methods("PUT")
 	r.HandleFunc("/v1/nodes/{fingerprint}", h.ReleaseLicense).Methods("DELETE")
 }
 
+func (h *handler) HealthCheck(w http.ResponseWriter, r *http.Request) {
+	w.WriteHeader(http.StatusOK)
+}
+
 func (h *handler) ClaimLicense(w http.ResponseWriter, r *http.Request) {
 	fingerprint := mux.Vars(r)["fingerprint"]