firecracker-microvm/firecracker · error

API thread spawn failed.

Error message

API thread spawn failed.

What it means

Error "API thread spawn failed." thrown in firecracker-microvm/firecracker.

Source

Thrown at src/firecracker/src/api_server_adapter.rs:214

        .try_clone()
        .expect("Failed to clone API kill switch");

    server
        .add_kill_switch(api_kill_switch_clone)
        .expect("Cannot add HTTP server kill switch");

    // Start the separate API thread.
    let api_thread = thread::Builder::new()
        .name("fc_api".to_owned())
        .spawn(move || {
            ApiServer::new(to_vmm, from_vmm, to_vmm_event_fd).run(
                server,
                process_time_reporter,
                &api_seccomp_filter,
                api_payload_limit,
            );
        })
        .expect("API thread spawn failed.");

    let mut event_manager = EventManager::new().expect("Unable to create EventManager");

    // Create the firecracker metrics object responsible for periodically printing metrics.
    let firecracker_metrics = Arc::new(Mutex::new(super::metrics::PeriodicMetrics::new()));
    event_manager.add_subscriber(firecracker_metrics.clone());

    // Configure, build and start the microVM.
    let build_result = match config_json {
        Some(json) => super::build_microvm_from_json(
            seccomp_filters,
            &mut event_manager,
            json,
            instance_info,
            boot_timer_enabled,
            pci_enabled,
            mmds_size_limit,
            metadata_json,

View on GitHub (pinned to 0a745def42)

Solutions

1. Check system thread limits (ulimit -u, cgroup pids.max) and available memory; thread spawn fails on resource exhaustion.
2. Inspect the OS error from the failed spawn for the precise cause.

When it happens

Trigger: Thrown at src/firecracker/src/api_server_adapter.rs:214 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of firecracker-microvm/firecracker@0a745def42 (2026-08-19). Data as JSON: /api/errors/d13e6652d233f981. Report an issue: GitHub.