minikube

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title	date	weight	description
Drivers	2019-07-31	4	How to create a new VM Driver

This document is written for contributors who are familiar with minikube, who would like to add support for a new VM driver.

minikube relies on docker-machine drivers to manage machines. This document discusses how to modify minikube, so that this driver may be used by minikube start --driver=<new_driver>.

Creating a new driver

See https://github.com/machine-drivers, the fork where all new docker-machine drivers are located.

Builtin vs External Drivers

Most drivers are built-in: they are included into minikube as a code dependency, so no further installation is required. There are two primary cases you may want to use an external driver:

The driver has a code dependency which minikube should not rely on due to platform incompatibilities (kvm2) or licensing
The driver needs to run with elevated permissions (hyperkit)

External drivers are instantiated by executing a command docker-machine-driver-<name>, which begins an RPC server which minikube will talk to.

Integrating a driver

The integration process is effectively 3 steps.

Create a driver shim within k8s.io/minikube/pkg/minikube/drivers
- Add Go build tag for the supported operating systems
- Define the driver metadata to register in DriverDef
Add import in pkg/minikube/cluster/default_drivers.go so that the driver may be included by the minikube build process.

The driver shim

The primary duty of the driver shim is to register a VM driver with minikube, and translate minikube VM hardware configuration into a format that the driver understands.

Registering your driver

The godoc of registry is available here: https://godoc.org/k8s.io/minikube/pkg/minikube/registry

DriverDef is the main struct to define a driver metadata. Essentially, you need to define 4 things at most, which is pretty simple once you understand your driver well:

Name: unique name of the driver, it will be used as the unique ID in registry and as --driver option in minikube command
Builtin: true if the driver should be builtin to minikube (preferred). false otherwise.
ConfigCreator: how to translate a minikube config to driver config. The driver config will be persistent on your $USER/.minikube directory. Most likely the driver config is the driver itself.
DriverCreator: Only needed when driver is builtin, to instantiate the driver instance.

Integration example: vmwarefusion

All drivers are located in k8s.io/minikube/pkg/minikube/drivers. Take vmwarefusion as an example:

// +build darwin

package vmwarefusion

import (
    "github.com/docker/machine/drivers/vmwarefusion"
    "github.com/docker/machine/libmachine/drivers"
    cfg "k8s.io/minikube/pkg/minikube/config"
    "k8s.io/minikube/pkg/minikube/constants"
    "k8s.io/minikube/pkg/minikube/localpath"
    "k8s.io/minikube/pkg/minikube/registry"
)

func init() {
    registry.Register(registry.DriverDef{
        Name:          "vmwarefusion",
        Builtin:       true,
        ConfigCreator: createVMwareFusionHost,
        DriverCreator: func() drivers.Driver {
            return vmwarefusion.NewDriver("", "")
        },
    })
}

func createVMwareFusionHost(config cfg.ClusterConfig) interface{} {
    d := vmwarefusion.NewDriver(config.Name, localpath.MiniPath()).(*vmwarefusion.Driver)
    d.Boot2DockerURL = download.LocalISOResource(config.MinikubeISO)
    d.Memory = config.Memory
    d.CPU = config.CPUs
    d.DiskSize = config.DiskSize
    d.SSHPort = 22
    d.ISO = d.ResolveStorePath("boot2docker.iso")
    return d
}

Within the init() function, register a DriverDef in registry. Specify the metadata in the DriverDef. As mentioned earlier, it's builtin, so you also need to specify DriverCreator to tell minikube how to create a drivers.Driver.
Another important thing is vmwarefusion only runs on MacOS. You need to add a build tag on top so it only runs on MacOS, so that the releases on Windows and Linux won't have this driver in registry.
Last but not least, import the driver in pkg/minikube/cluster/default_drivers.go to include it in build.

Any Questions: please ping your friend @anfernee or the #minikube Slack channel.

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