Simplify the runtime configuration

[samuelkarp]

The runtime configuration is fairly complicated and has a number of fields that need reasonable defaults.

• firecracker_binary_path - the relative path default is unreasonable, since the working directory changes every time containerd executes a new container (working directory is inside the container bundle)
• socket_path - needs a reasonable default, probably relative inside the working directory/bundle
• kernel_image_path - could use a default lookup path
• kernel_args - needs a reasonable default
• root_drive - could use a default lookup path
• cpu_count - might want to pick this dynamically from the OCI spec, with perhaps a reasonable default
• console - should it default to "stdio"?

Related to #57

[IRCody]

socket_path - needs a reasonable default, probably relative inside the working directory/bundle

Not sure about all the others but I think ./firecracker.sock makes sense as a default for socket_path.

[samuelkarp]

Not sure about all the others but I think ./firecracker.sock makes sense as a default for socket_path.

Yep, I think so too.

[xibz]

I believe the jailer socket path (not settable) is api.socket and in firecracker's docs they use firecracker.socket in their getting started guide. Should we try to be consistent? If the jailer is on by default, may be best to go with api.socket?

[samuelkarp]

cpu_count - might want to pick this dynamically from the OCI spec, with perhaps a reasonable default

Opened #76 to track the use-case for separate VM sizing parameters for different VMs

[samuelkarp]

firecracker_binary_path - the relative path default is unreasonable, since the working directory changes every time containerd executes a new container (working directory is inside the container bundle)

This has been changed in firecracker-go-sdk and we've now inherited that change such that it defaults to firecracker on $PATH. This is a much more reasonable default. I'll remove this item from the overview list.

[samuelkarp]

I believe the jailer socket path (not settable) is api.socket and in firecracker's docs they use firecracker.socket in their getting started guide. Should we try to be consistent? If the jailer is on by default, may be best to go with api.socket?

That looks accurate. I think for now I'm going to hard-code the socket (instead of making it configurable) as ./firecracker.sock, but when we take a look at jailer integration (#122) we'll need to revisit this.

[samuelkarp]

kernel_args - needs a reasonable default

Per discussion with @nmeyerhans, my plan is to use "console=ttyS0 noapic reboot=k panic=1 pci=off nomodules rw" as the default for now.