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⛈️ fix: MCP Reconnection Storm Prevention with Circuit Breaker, Backoff, and Tool Stubs (#12162)

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* fix: MCP reconnection stability - circuit breaker, throttling, and cooldown retry

* Comment and logging cleanup

* fix broken tests
This commit is contained in:
matt burnett 2026-03-10 11:21:36 -07:00 • committed by GitHub
parent cfbe812d63
commit ad5c51f62b
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GPG key ID: B5690EEEBB952194
9 changed files with 736 additions and 38 deletions
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66
api/server/services/MCP.js
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@ -34,6 +34,39 @@ const { reinitMCPServer } = require('./Tools/mcp');
const { getAppConfig } = require('./Config');
const { getLogStores } = require('~/cache');
const lastReconnectAttempts = new Map();
const RECONNECT_THROTTLE_MS = 10_000;
const missingToolCache = new Map();
const MISSING_TOOL_TTL_MS = 10_000;
const unavailableMsg =
"This tool's MCP server is temporarily unavailable. Please try again shortly.";
/**
* @param {string} toolName
* @param {string} serverName
*/
function createUnavailableToolStub(toolName, serverName) {
const normalizedToolKey = `${toolName}${Constants.mcp_delimiter}${normalizeServerName(serverName)}`;
const _call = async () => unavailableMsg;
const toolInstance = tool(_call, {
schema: {
type: 'object',
properties: {
input: { type: 'string', description: 'Input for the tool' },
},
required: [],
},
name: normalizedToolKey,
description: unavailableMsg,
responseFormat: AgentConstants.CONTENT_AND_ARTIFACT,
});
toolInstance.mcp = true;
toolInstance.mcpRawServerName = serverName;
return toolInstance;
}
function isEmptyObjectSchema(jsonSchema) {
return (
jsonSchema != null &&
@ -211,6 +244,16 @@ async function reconnectServer({
logger.debug(
`[MCP][reconnectServer] serverName: ${serverName}, user: ${user?.id}, hasUserMCPAuthMap: ${!!userMCPAuthMap}`,
);
const throttleKey = `${user.id}:${serverName}`;
const now = Date.now();
const lastAttempt = lastReconnectAttempts.get(throttleKey) ?? 0;
if (now - lastAttempt < RECONNECT_THROTTLE_MS) {
logger.debug(`[MCP][reconnectServer] Throttled reconnect for ${serverName}`);
return null;
}
lastReconnectAttempts.set(throttleKey, now);
const runId = Constants.USE_PRELIM_RESPONSE_MESSAGE_ID;
const flowId = `${user.id}:${serverName}:${Date.now()}`;
const flowManager = getFlowStateManager(getLogStores(CacheKeys.FLOWS));
@ -267,7 +310,7 @@ async function reconnectServer({
userMCPAuthMap,
forceNew: true,
returnOnOAuth: false,
connectionTimeout: Time.TWO_MINUTES,
connectionTimeout: Time.THIRTY_SECONDS,
});
} finally {
// Clean up abort handler to prevent memory leaks
@ -332,7 +375,7 @@ async function createMCPTools({
});
if (!result || !result.tools) {
logger.warn(`[MCP][${serverName}] Failed to reinitialize MCP server.`);
return;
return [];
}
const serverTools = [];
@ -402,6 +445,14 @@ async function createMCPTool({
/** @type {LCTool | undefined} */
let toolDefinition = availableTools?.[toolKey]?.function;
if (!toolDefinition) {
const cachedAt = missingToolCache.get(toolKey);
if (cachedAt && Date.now() - cachedAt < MISSING_TOOL_TTL_MS) {
logger.debug(
`[MCP][${serverName}][${toolName}] Tool in negative cache, returning unavailable stub.`,
);
return createUnavailableToolStub(toolName, serverName);
}
logger.warn(
`[MCP][${serverName}][${toolName}] Requested tool not found in available tools, re-initializing MCP server.`,
);
@ -415,11 +466,17 @@ async function createMCPTool({
streamId,
});
toolDefinition = result?.availableTools?.[toolKey]?.function;
if (!toolDefinition) {
missingToolCache.set(toolKey, Date.now());
}
}
if (!toolDefinition) {
logger.warn(`[MCP][${serverName}][${toolName}] Tool definition not found, cannot create tool.`);
return;
logger.warn(
`[MCP][${serverName}][${toolName}] Tool definition not found, returning unavailable stub.`,
);
return createUnavailableToolStub(toolName, serverName);
}
return createToolInstance({
@ -720,4 +777,5 @@ module.exports = {
getMCPSetupData,
checkOAuthFlowStatus,
getServerConnectionStatus,
createUnavailableToolStub,
};