feat(proxyd): impl proxyd_healthz method (#8658)

proxyd/proxyd/backend.go

@@ -17,6 +17,7 @@ import (
 	"sync"
 	"time"
 
+	sw "github.com/ethereum-optimism/optimism/proxyd/pkg/avg-sliding-window"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -24,8 +25,6 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/xaionaro-go/weightedshuffle"
 	"golang.org/x/sync/semaphore"
-
-	sw "github.com/ethereum-optimism/optimism/proxyd/pkg/avg-sliding-window"
 )
 
 const (
@@ -285,6 +284,8 @@ type indexedReqRes struct {
 	res   *RPCRes
 }
 
+const proxydHealthzMethod = "proxyd_healthz"
+
 const ConsensusGetReceiptsMethod = "consensus_getReceipts"
 
 const ReceiptsTargetDebugGetRawReceipts = "debug_getRawReceipts"

proxyd/proxyd/server.go

@@ -435,6 +435,16 @@ func (s *Server) handleBatchRPC(ctx context.Context, reqs []json.RawMessage, isL
 			continue
 		}
 
+		// Simple health check
+		if len(reqs) == 1 && parsedReq.Method == proxydHealthzMethod {
+			res := &RPCRes{
+				ID:      parsedReq.ID,
+				JSONRPC: JSONRPCVersion,
+				Result:  "OK",
+			}
+			return []*RPCRes{res}, false, "", nil
+		}
+
 		if err := ValidateRPCReq(parsedReq); err != nil {
 			RecordRPCError(ctx, BackendProxyd, MethodUnknown, err)
 			responses[i] = NewRPCErrorRes(nil, err)