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Actions API Request

Firecracker microVMs can execute actions that can be triggered via PUT requests on the /actions resource.

Details about the required fields can be found in the swagger definition.

InstanceStart

The InstanceStart action powers on the microVM and starts the guest OS. It does not have a payload. It can only be successfully called once.

InstanceStart Example

curl --unix-socket ${socket} -i \
     -X PUT "http://localhost/actions" \
     -d '{ "action_type": "InstanceStart" }'

FlushMetrics

The FlushMetrics action flushes the metrics on user demand.

FlushMetrics Example

curl --unix-socket /tmp/firecracker.socket -i \
    -X PUT "http://localhost/actions" \
    -d '{ "action_type": "FlushMetrics" }'

SendCtrlAltDel

This action requests an orderly shutdown of the microVM from the host. Since Firecracker exits when the guest powers off (CPU reset), SendCtrlAltDel can be used to trigger a clean shutdown of the microVM. The mechanism differs per architecture, but the API request is the same on both.

On x86_64, this action sends the CTRL+ALT+DEL key sequence to the microVM. By convention, this sequence has been used to trigger a soft reboot and, as such, most Linux distributions perform an orderly shutdown and reset upon receiving this keyboard input. Firecracker emulates a standard AT keyboard, connected via an i8042 controller. Driver support for both these devices needs to be present in the guest OS. For Linux, that means the guest kernel needs CONFIG_SERIO_I8042 and CONFIG_KEYBOARD_ATKBD.

On aarch64, this action injects a virtual power-button press. Firecracker exposes a PL061 GPIO controller and describes a gpio-keys power button (mapped to KEY_POWER) in the device tree. Driver support needs to be present in the guest OS; for Linux that means CONFIG_GPIOLIB, CONFIG_GPIO_PL061, CONFIG_INPUT_KEYBOARD and CONFIG_KEYBOARD_GPIO, plus a userspace consumer of the power-key event (for example systemd-logind with the default HandlePowerKey=poweroff).

Note

At boot time, the Linux driver for i8042 spends a few tens of milliseconds probing the device. This can be disabled by using these kernel command line parameters:

i8042.noaux i8042.nomux i8042.nopnp i8042.dumbkbd

SendCtrlAltDel Example

curl --unix-socket /tmp/firecracker.socket -i \
    -X PUT "http://localhost/actions" \
    -d '{ "action_type": "SendCtrlAltDel" }'