Unable to use kaniko-action with runner in GKE with workload identity

[bymarshall]

As is documented here, workload identity in GKE is one of the possible methods to authenticate kaniko and push images to GCR:
https://github.com/GoogleContainerTools/kaniko#pushing-to-gcr-using-workload-identity

I'm trying to use this action with a github action runner in a GKE Cluster with workload identity enabled, however, since I'm not providing a ~/.docker/config.json file, the job is always failing with the following error:

error building image: /kaniko/.docker/config.json: read /kaniko/.docker/config.json: is a directory
Error: The process '/usr/local/bin/docker' failed with exit code 1

In order to fix this problem and provide compatibility, I think you should mount the ~/.docker directory instead of the config.json file, currently if this file doesn't exist, docker is mounting it as a folder instead of a file and kaniko is trying to use it.

The modification should look like this:

export const generateArgs = (inputs: Inputs, outputDir: string): string[] => {
  const args = [
    // docker args
    'run',
    '--rm',
    '-v',
    `${path.resolve(inputs.context)}:/kaniko/action/context:ro`,
    '-v',
    `${outputDir}:/kaniko/action/output`,
    '-v',
    `${os.homedir()}/.docker:/kaniko/.docker:ro`,

[Jerome1337]

Related to #84 (comment)