The configuration of the instance to launch is defined via a series of HTTP requests. These commands need to run within the second terminal window.
Set the guest kernel
The first configuration is to define the boot source and the kernel to use. It will look in the same directory as the Firecracker binary. A series of boot arguments can be passed to the Kernel to configure how it launches.
curl --unix-socket /tmp/firecracker.sock -i \
-X PUT 'http://localhost/boot-source' \
-H 'Accept: application/json' \
-H 'Content-Type: application/json' \
-d '{
"kernel_image_path": "./hello-vmlinux.bin",
"boot_args": "console=ttyS0 reboot=k panic=1 pci=off"
}'
The response of 204 No Content indicates that the request was successful.
Set the guest rootfs
Next, define the rootfs and the guest operating system that will be booted.
curl --unix-socket /tmp/firecracker.sock -i \
-X PUT 'http://localhost/drives/rootfs' \
-H 'Accept: application/json' \
-H 'Content-Type: application/json' \
-d '{
"drive_id": "rootfs",
"path_on_host": "./hello-rootfs.ext4",
"is_root_device": true,
"is_read_only": false
}'
Firecracker outputs various logs and metrics about how the system is performing to external systems. For now, disable to metrics using the following command:
curl -fsS --unix-socket /tmp/firecracker.sock -i \
-X PUT "http://localhost/logger" \
-H "accept: application/json" \
-H "Content-Type: application/json" \
-d '{
"log_fifo": "/dev/null",
"metrics_fifo": "/dev/null",
"level": "Error",
"show_level": true,
"show_log_origin": false
}'
Start the guest machine
The instance is now configured and can be started. This is done by issuing a InstanceStart action.
curl --unix-socket /tmp/firecracker.sock -i \
-X PUT 'http://localhost/actions' \
-H 'Accept: application/json' \
-H 'Content-Type: application/json' \
-d '{
"action_type": "InstanceStart"
}'
Within the first terminal window, you should see the VM start booting and after a few seconds, a login prompt will appear. If you see the error KVM_EXIT_FAIL_ENTRY then a problem has occurred.
The Firecracker is the parent process ID that will manage the instance. This can be viewed within the process tree.
ps aux | grep firecracker
The VM is running as a KVM instance that is also listed as a process.
ps aux | grep kvm
