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Firecracker Integration Tests

The tests herein are meant to uphold the security, quality, and performance contracts of Firecracker.

Running

To run all tests:

tools/devtool test

This will download test microvm images from the default test resource S3 bucket and run all available tests.

To run tests from specific directories and/or files:

tools/devtool test -- <test_dir_or_file_path>...

The testing system is built around pytest. Any parameters passed to tools/devtool test -- are passed to the pytest command. devtool is used to automate fetching of test dependencies (useful for continuous integration) and to sandbox test runs (useful for development environments). If you are not interested in these capabilities, use pytest directly, either from inside the container:

tools/devtool shell -p
pytest [<pytest argument>...]

Or natively on your dev box:

python3 -m pytest [<pytest argument>...]

For help on usage, see tools/devtool help.

Output

  • Output, including testrun results, goes to stdout. Errors go to stderr.

Dependencies

  • A bare-metal Linux host with uname -r >= 4.14.
  • Docker.

Adding Tests

Tests can be added in any (existing or new) sub-directory of tests/, in files named test_*.py.

Fixtures can be used to quickly build Firecracker microvm integration tests that run on all microvm images in s3://spec.ccfc.min/img/.

For example, the test below makes use of the test_microvm_any fixture and will be run on every microvm image in the bucket, each as a separate test case.

def test_with_any_microvm(test_microvm_any):
    response = test_microvm_any.machine_cfg.put(
        vcpu_count=2
    )
    assert(test_microvm_any.api_session.is_good_response(response.status_code))

    # [...]

    response = test_microvm_any.actions.put(action_type='InstanceStart')
    assert(test_microvm_any.api_session.is_good_response(response.status_code))

If instead of test_microvm_any, a capability-based fixture would be used, e.g., test_microvm_with_net, then the test would instead run on all microvm images with the capability:net tag.

To see what fixtures are available, inspect conftest.py.

Adding Microvm Images

Simply place the microvm image under s3://spec.ccfc.min/img/. The layout is:

s3://<bucket-url>/img/
    <microvm_test_image_folder_n>/
        kernel/
            <optional_kernel_name.>vmlinux.bin
        fsfiles/
            <rootfs_name>rootfs.ext4
            <other_fsfile_n>
            ...
        <other_resource_n>
        ...
    ...

Then, tag <microvm_test_image_folder_n> with:

TagSet = [{"key": "capability:<cap_name>", "value": ""}, ...]

For example, this can be done from the AWS CLI with:

aws s3api put-object-tagging                    \
    --bucket ${bucket_name}                     \
    --key img/${microvm_test_image_folder_n}    \
    --tagging "TagSet=[{Key=capability:${cap_name},Value=''}]"

Adding Fixtures

By default, pytest makes all fixtures in conftest.py available to all test functions. You can also create conftest.py in sub-directories containing tests, or define fixtures directly in test files. See pytest documentation for details.

Working With Guest Files

There are helper methods for writing to and reading from a guest filesystem. For example, to overwrite the guest init process and later extract a log:

def test_with_any_microvm_and_my_init(test_microvm_any):
    # [...]
    test_microvm_any.slot.fsfiles['mounted_root_fs'].copy_to(my_init, 'sbin/')
    # [...]
    test_microvm_any.slot.fsfiles['mounted_root_fs'].copy_from('logs/', 'log')

copy_to() source paths are relative to the host root and destination paths are relative to the mounted_root_fs root. Vice versa for copy_from().

Copying files to/from a guest file system while the guest is running results in undefined behavior.

Example Manual Testrun

Running on an EC2 .metal instance with an Amazon Linux 2 AMI:

# Get firecracker
yum install -y git
git clone https://github.com/firecracker-microvm/firecracker.git

# Run all tests
cd firecracker
tools/devtool test

Terminology

  • Testrun: A sandboxed run of all (or a selection of) integration tests.
  • Test Session: A pytest testing session. One per testrun. A Testrun will start a Test Session once the sandbox is created.
  • Test: A function named test_ from this tree, that ensures a feature, functional parameter, or quality metric of Firecracker. Should assert or raise an exception if it fails.
  • Fixture: A function that returns an object that makes it very easy to add Tests: E.g., a spawned Firecracker microvm. Fixtures are functions marked with @pytest.fixture from a files named either conftest.py, or from files where tests are found. See pytest documentation on fixtures.
  • Test Case: An element from the cartesian product of a Test and all possible states of its parameters (including its fixtures).

FAQ

Q1: I have a shell script that runs my tests and I don't want to rewrite it.
A1: Insofar as it makes sense, you should write it as a python test function. However, you can always call the script from a shim python test function. You can also add it as a microvm image resource in the s3 bucket (and it will be made available under microvm.slot.path) or copy it over to a guest filesystem as part of your test.

Q2: I want to add more tests that I don't want to commit to the Firecracker repository.
A2: Before a testrun or test session, just add your test directory under tests/. pytest will discover all tests in this tree.

Q3: I want to have my own test fixtures, and not commit them in the repo.
A3: Add a conftest.py file in your test directory, and place your fixtures there. pytest will bring them into scope for all your tests.

Q4: I want to use more/other microvm test images, but I don't want to add them to the common s3 bucket.
A4: There are two options to achieve this:

  1. Pass the -i / --local-images-path option to testrun.sh. This will use local versions of the images found in the common s3 bucket.
  2. Leverage pytest to build a self-contained set of tests that use your own test bucket.
    • Create the s3 test bucket.
    • Create a new test directory as per A2, and a fixture file as per A3.
    • Within the new fixture, instantiate a MicrovmImageS3Fetcher for your s3 bucket.
    • Using that MicrovmImageS3Fetcher object, create a fixture similar to the test_microvm_* fixtures in in conftest.py, and pass that as an argument to your tests.

Implementation Goals

  • Easily run tests manually on a development/test machine, and in a continuous integration environments.
  • Each test should be independent, and self-contained. Tests will time out, expect a clean environment, and leave a clean environment behind.
  • Always run with the latest dependencies and resources.

Choice of Pytest & Dependencies

Pytest was chosen because:

  • Python makes it easy to work in the clouds.
  • Python has built-in sandbox (virtual environment) support.
  • pytest has great test discovery and allows for simple, function-like tests.
  • pytest has powerful test fixture support.

Test System TODOs

Note: The below TODOs are also mentioned in their respective code files.

Features

  • Modify MicrovmImageS3Fetcher to make the above FAQ possible (the borg pattern is wrong for this).
  • A fixture for interacting with microvms via SSH.
  • Support generating fixtures with more than one capability. This is supported by the MicrovmImageS3Fetcher, but not plumbed through.
  • Use the Firecracker Open API spec to populate Microvm API resource URLs.
  • Manage output better: handle quietness levels, and use pytest reports.
  • Do the testrun in a container for better insulation.
  • Add support for non-Rust style checks.
  • Event-based monitoring of microvm socket file creation to avoid while spins.
  • Self-tests (e.g., Tests that test the testing system, python3 style tests).

Implementation

  • Run build tests / unit tests with --release once https://github.com/edef1c/libfringe/issues/75 is fixed.
  • Ensure that we're running in the correct path of the Firecracker repo.
  • Looking into pytest-ordering to ensure test order.
  • #[test] fn enable_disable_stdin_test() from vmm/src/lib.rs fails if pytest is allowed to record stdin and stdout. Currently this is worked around by running pytest with --capture=no, which uglifies the output.
  • The code would be less repetitive with a function that wraps subprocess.run('<command>, shell=True, check=True).
  • Create an integrated, layered say system across the test runner and pytest (probably based on an environment variable).
  • Per test function dependency installation would make tests easer to write.
  • Type hinting is used sparsely across tests/* python module. The code would be more easily understood with consistent type hints everywhere.

Bug fixes

  • Fix the /install-kcov.sh bug.

Further Reading

Contributing to this testing system requires a dive deep on pytest.