xmanager: `xmanager launch` cannot resolve `'docker'` in subprocess

Hi All,

I am trying to run the example xmanager launch ./xmanager/examples/cifar10_tensorflow/launcher.py. However, I get the following error. Do you have any suggestion where this error may coming from and how could I fix it?

I1020 10:57:30.250377 4561079808 build_image.py:134] Local docker: {'Platform': {'Name': 'Docker Engine - Community'}, 'Components': [{'Name': 'Engine', 'Version': '20.10.8', 'Details': {'ApiVersion': '1.41', 'Arch': 'amd64', 'BuildTime': '2021-07-30T19:52:10.000000000+00:00', 'Experimental': 'false', 'GitCommit': '75249d8', 'GoVersion': 'go1.16.6', 'KernelVersion': '5.10.47-linuxkit', 'MinAPIVersion': '1.12', 'Os': 'linux'}}, {'Name': 'containerd', 'Version': '1.4.9', 'Details': {'GitCommit': 'e25210fe30a0a703442421b0f60afac609f950a3'}}, {'Name': 'runc', 'Version': '1.0.1', 'Details': {'GitCommit': 'v1.0.1-0-g4144b63'}}, {'Name': 'docker-init', 'Version': '0.19.0', 'Details': {'GitCommit': 'de40ad0'}}], 'Version': '20.10.8', 'ApiVersion': '1.41', 'MinAPIVersion': '1.12', 'GitCommit': '75249d8', 'GoVersion': 'go1.16.6', 'Os': 'linux', 'Arch': 'amd64', 'KernelVersion': '5.10.47-linuxkit', 'BuildTime': '2021-07-30T19:52:10.000000000+00:00'}
I1020 10:57:30.250654 4561079808 docker_lib.py:64] Building Docker image
Dockerfile:

FROM gcr.io/deeplearning-platform-release/tf2-gpu.2-6

RUN if ! id 1000; then useradd -m -u 1000 clouduser; fi

ENV LANG=C.UTF-8
RUN apt-get update && apt-get install -y git netcat
RUN python -m pip install --upgrade pip setuptools
COPY cifar10_tensorflow/requirements.txt /cifar10_tensorflow/requirements.txt
RUN python -m pip install -r cifar10_tensorflow/requirements.txt
COPY cifar10_tensorflow/ /cifar10_tensorflow
RUN chown -R 1000:root /cifar10_tensorflow && chmod -R 775 /cifar10_tensorflow
WORKDIR cifar10_tensorflow

COPY entrypoint.sh ./entrypoint.sh
RUN chown -R 1000:root ./entrypoint.sh && chmod -R 775 ./entrypoint.sh

ENTRYPOINT ["./entrypoint.sh"]

Size of Docker input: 7.0 kB
Building Docker image, please wait...
Traceback (most recent call last):
  File "/Users/chuchu/anaconda3/envs/jax/bin/xmanager", line 8, in <module>
    sys.exit(entrypoint())
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/cli/cli.py", line 65, in entrypoint
    app.run(main)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/absl/app.py", line 303, in run
    _run_main(main, args)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/absl/app.py", line 251, in _run_main
    sys.exit(main(argv))
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/cli/cli.py", line 41, in main
    app.run(m.main, argv=argv)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/absl/app.py", line 303, in run
    _run_main(main, args)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/absl/app.py", line 251, in _run_main
    sys.exit(main(argv))
  File "/Users/chuchu/Documents/gt_local/try/xmanager/examples/cifar10_tensorflow/launcher.py", line 48, in main
    args={},
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm/core.py", line 484, in package
    return cls._async_packager.package(packageables)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm/async_packager.py", line 104, in package
    executables = self._package_batch(packageables)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm_local/packaging/router.py", line 56, in package
    for packageable in packageables
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm_local/packaging/router.py", line 56, in <listcomp>
    for packageable in packageables
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm/pattern_matching.py", line 113, in apply
    return case.handle(*values)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm_local/packaging/router.py", line 27, in _visit_caip_spec
    packageable.executable_spec)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm_local/packaging/cloud.py", line 153, in package_cloud_executable
    return _CLOUD_PACKAGING_ROUTER(packageable, executable_spec)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm/pattern_matching.py", line 113, in apply
    return case.handle(*values)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/xm_local/packaging/cloud.py", line 129, in _package_python_container
    packageable.env_vars, push_image_tag))
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/cloud/build_image.py", line 110, in build
    image_name, project, bucket)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/cloud/build_image.py", line 154, in build_by_dockerfile
    show_docker_command_progress=_SHOW_DOCKER_COMMAND_PROGRESS.value)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/cloud/docker_lib.py", line 70, in build_docker_image
    dockerfile, show_docker_command_progress)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/site-packages/xmanager/cloud/docker_lib.py", line 113, in _build_image_with_docker_command
    subprocess.run(command, check=True, env={'DOCKER_BUILDKIT': '1'})
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/subprocess.py", line 488, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/subprocess.py", line 800, in __init__
    restore_signals, start_new_session)
  File "/Users/chuchu/anaconda3/envs/jax/lib/python3.7/subprocess.py", line 1551, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'docker': 'docker'