langgenius/dify · error · Error

Cannot start the E2E Agent backend because ${agentBackendHos

Error message

Cannot start the E2E Agent backend because ${agentBackendHost}:${agentBackendPort} is already in use.${listenerMessage}

What it means

Error "Cannot start the E2E Agent backend because ${agentBackendHost}:${agentBackendPort} is already in use.${listenerMessage}" thrown in langgenius/dify.

Source

Thrown at e2e/scripts/setup.ts:353

      '--no-sync',
      'flask',
      'run',
      '--host',
      apiBindHost,
      '--port',
      String(apiPort),
    ],
    cwd: apiDir,
    env,
  })
}

export const startAgentBackend = async () => {
  if (await isTcpPortReachable(agentBackendHost, agentBackendPort)) {
    const listenerDescription = await getTcpPortListenerDescription(agentBackendPort)
    const listenerMessage = listenerDescription ? `\n\nPort listener:\n${listenerDescription}` : ''

    throw new Error(
      `Cannot start the E2E Agent backend because ${agentBackendHost}:${agentBackendPort} is already in use.${listenerMessage}`,
    )
  }

  await runForegroundProcess({
    command: 'uv',
    args: [
      'run',
      '--project',
      '.',
      '--extra',
      'server',
      'uvicorn',
      'dify_agent.server.app:app',
      '--host',
      agentBackendBindHost,
      '--port',
      String(agentBackendPort),

View on GitHub (pinned to ef8544b173)

When it happens

Trigger: Thrown at e2e/scripts/setup.ts:353 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langgenius/dify@ef8544b173 (2026-08-12). Data as JSON: /api/errors/2676118d4cdf1120. Report an issue: GitHub.