fix: ignore known blocks during publishing (#6457)

packages/beacon-node/src/api/impl/beacon/blocks/index.ts

@@ -8,7 +8,7 @@ import {BlockSource, getBlockInput, ImportBlockOpts, BlockInput} from "../../../
 import {promiseAllMaybeAsync} from "../../../../util/promises.js";
 import {isOptimisticBlock} from "../../../../util/forkChoice.js";
 import {computeBlobSidecars} from "../../../../util/blobs.js";
-import {BlockError, BlockErrorCode} from "../../../../chain/errors/index.js";
+import {BlockError, BlockErrorCode, BlockGossipError} from "../../../../chain/errors/index.js";
 import {OpSource} from "../../../../metrics/validatorMonitor.js";
 import {NetworkEvent} from "../../../../network/index.js";
 import {ApiModules} from "../../types.js";
@@ -83,6 +83,13 @@ export function getBeaconBlockApi({
           try {
             await validateGossipBlock(config, chain, signedBlock, fork);
           } catch (error) {
+            if (error instanceof BlockGossipError && error.type.code === BlockErrorCode.ALREADY_KNOWN) {
+              chain.logger.debug("Ignoring known block during publishing", valLogMeta);
+              // Blocks might already be published by another node as part of a fallback setup or DVT cluster
+              // and can reach our node by gossip before the api. The error can be ignored and should not result in a 500 response.
+              return;
+            }
+
             chain.logger.error("Gossip validations failed while publishing the block", valLogMeta, error as Error);
             chain.persistInvalidSszValue(
               chain.config.getForkTypes(slot).SignedBeaconBlock,