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Container Structure Tests

The Container Structure Tests provide a powerful framework to validate the structure of a container image. These tests can be used to check the output of commands in an image, as well as verify metadata and contents of the filesystem.

Tests can be run either through a standalone binary, or through a Docker image.

Installation

OS X

curl -LO https://storage.googleapis.com/container-structure-test/latest/container-structure-test-darwin-amd64 && chmod +x container-structure-test-darwin-amd64 && sudo mv container-structure-test-darwin-amd64 /usr/local/bin/container-structure-test

Linux

curl -LO https://storage.googleapis.com/container-structure-test/latest/container-structure-test-linux-amd64 && chmod +x container-structure-test-linux-amd64 && sudo mv container-structure-test-linux-amd64 /usr/local/bin/container-structure-test

If you want to avoid using sudo:

curl -LO https://storage.googleapis.com/container-structure-test/latest/container-structure-test-linux-amd64 && chmod +x container-structure-test-linux-amd64 && mkdir -p $HOME/bin && export PATH=$PATH:$HOME/bin && mv container-structure-test-linux-amd64 $HOME/bin/container-structure-test

Additionally, a container image for running tests through Google Cloud Builder can be found at gcr.io/gcp-runtimes/container-structure-test:latest.

Setup

To use container structure tests to validate your containers, you need the following:

  • The container structure test binary or docker image
  • A container image to test against
  • A test .yaml or .json file with user defined structure tests to run inside of the specified container image

Note that the test framework looks for the provided image in the local Docker daemon (if it is not provided as a tar). The -pull flag can optionally be provided to force a pull of a remote image before running the tests.

Example Run

An example run of the test framework:

./structure-test test --image gcr.io/google-appengine/python \
--config python_test_config.yaml

This command will run the tests on the Google App Engine Python image, with verbose logging, using the python_test_config.yaml test config.

Tests within this framework are specified through a YAML or JSON config file, which is provided to the test driver as the last positional argument of the command. Multiple config files may be specified in a single test run. The config file will be loaded in by the test driver, which will execute the tests in order. Within this config file, four types of tests can be written:

  • Command Tests (testing output/error of a specific command issued)
  • File Existence Tests (making sure a file is, or isn't, present in the file system of the image)
  • File Content Tests (making sure files in the file system of the image contain, or do not contain, specific contents)
  • Metadata Test, singular (making sure certain container metadata is correct)

Command Tests

Command tests ensure that certain commands run properly in the target image. Regexes can be used to check for expected or excluded strings in both stdout and stderr. Additionally, any number of flags can be passed to the argument as normal.

Supported Fields:

This is the current schema version (v2.0.0).

  • Name (string, required): The name of the test
  • Setup ([][]string, optional): A list of commands (each with optional flags) to run before the actual command under test.
  • Teardown ([][]string, optional): A list of commands (each with optional flags) to run after the actual command under test.
  • Command (string, required): The command to run in the test.
  • Args ([]string, optional): The arguments to pass to the command.
  • EnvVars ([]EnvVar, optional): A list of environment variables to set for the individual test. See the Environment Variables section for more info.
  • Expected Output ([]string, optional): List of regexes that should match the stdout from running the command.
  • Excluded Output ([]string, optional): List of regexes that should not match the stdout from running the command.
  • Expected Error ([]string, optional): List of regexes that should match the stderr from running the command.
  • Excluded Error ([]string, optional): List of regexes that should not match the stderr from running the command.
  • Exit Code (int, optional): Exit code that the command should exit with.

Example:

commandTests:
  - name: "gunicorn flask"
    setup: [["virtualenv", "/env"], ["pip", "install", "gunicorn", "flask"]]
    command: "which"
    args: ["gunicorn"]
    expectedOutput: ["/env/bin/gunicorn"]
- name:  "apt-get upgrade"
  command: "apt-get"
  args: ["-qqs", "upgrade"]
  excludedOutput: [".*Inst.*Security.* | .*Security.*Inst.*"]
  excludedError: [".*Inst.*Security.* | .*Security.*Inst.*"]

Image Entrypoint

To avoid unexpected behavior and output when running commands in the containers, all entrypoints are overwritten by default. If your entrypoint is necessary for the structure of your container, use the setup field to call any scripts or commands manually before running the tests.

commandTests:
  ...
  setup: [["my_image_entrypoint.sh"]]
  ...

Intermediate Artifacts

Each command test run creates either a container (with the docker driver) or tar artifact (with the tar driver). By default, these are deleted after the test run finishes, but the -save flag can optionally be passed to keep these around. This would normally be used for debugging purposes.

File Existence Tests

File existence tests check to make sure a specific file (or directory) exist within the file system of the image. No contents of the files or directories are checked. These tests can also be used to ensure a file or directory is not present in the file system.

Supported Fields:

  • Name (string, required): The name of the test
  • Path (string, required): Path to the file or directory under test
  • ShouldExist (boolean, required): Whether or not the specified file or directory should exist in the file system
  • Permissions (string, optional): The expected Unix permission string (e.g. drwxrwxrwx) of the files or directory.
  • Uid (int, optional): The expected Unix user ID that has access to the file or directory.
  • Gid (int, optional): The expected Unix group ID that has access to the file or directory.
  • IsExecutableBy (string, optional): Checks if file is executable by a given user. One of owner, group, other or any

Example:

fileExistenceTests:
- name: 'Root'
  path: '/'
  shouldExist: true
  permissions: '-rw-r--r--'
  uid: 1000
  gid: 1000
  isExecutableBy: 'group'

File Content Tests

File content tests open a file on the file system and check its contents. These tests assume the specified file is a file, and that it exists (if unsure about either or these criteria, see the above File Existence Tests section). Regexes can again be used to check for expected or excluded content in the specified file.

Supported Fields:

  • Name (string, required): The name of the test
  • Path (string, required): Path to the file under test
  • ExpectedContents (string[], optional): List of regexes that should match the contents of the file
  • ExcludedContents (string[], optional): List of regexes that should not match the contents of the file

Example:

fileContentTests:
- name: 'Debian Sources'
  path: '/etc/apt/sources.list'
  expectedContents: ['.*httpredir\\.debian\\.org.*']
  excludedContents: ['.*gce_debian_mirror.*']

Metadata Test

The Metadata test ensures the container is configured correctly. All of these checks are optional.

Supported Fields:

  • Env ([]EnvVar): A list of environment variable key/value pairs that should be set in the container.
  • Labels ([]Label): A list of image labels key/value pairs that should be set on the container.
  • Entrypoint ([]string): The entrypoint of the container
  • Cmd ([]string): The CMD specified in the container.
  • Exposed Ports ([]string): The ports exposed in the container.
  • Volumes ([]string): The volumes exposed in the container.
  • Workdir (string): The default working directory of the container.

Example:

metadataTest:
  env:
    - key: foo
      value: baz
  labels:
    - key: 'com.example.vendor'
      value: 'ACME Incorporated'
  exposedPorts: ["8080", "2345"]
  volumes: ["/test"]
  entrypoint: []
  cmd: ["/bin/bash"]
  workdir: "/app"

License Tests

License tests check a list of copyright files and makes sure all licenses are allowed at Google. By default it will look at where Debian lists all copyright files, but can also look at an arbitrary list of files.

Supported Fields:

  • Debian (bool, required): If the image is based on Debian, check where Debian lists all licenses.
  • Files (string[], optional): A list of other files to check.

Example:

licenseTests:
- debian: true
  files: ["/foo/bar", "/baz/bat"]

Environment Variables

A list of environment variables can optionally be specified as part of the test setup. They can either be set up globally (for all test runs), or test-local as part of individual command test runs (see the Command Tests section above). Each environment variable is specified as a key-value pair. Unix-style environment variable substitution is supported.

To specify, add a section like this to your config:

globalEnvVars:
  - key: "VIRTUAL_ENV"
    value: "/env"
  - key: "PATH"
    value: "/env/bin:$PATH"

Running File Tests On Google Cloud Container Builder

This tool is released as a builder image, tagged as gcr.io/gcp-runtimes/container-structure-test, so you can specify tests in your cloudbuild.yaml:

steps:
# Build an image.
- name: 'gcr.io/cloud-builders/docker'
  args: ['build', '-t', 'gcr.io/$PROJECT_ID/image', '.']
# Test the image.
- name: 'gcr.io/gcp-runtimes/container-structure-test'
  args: ['-image', 'gcr.io/$PROJECT_ID/image', 'test_config.yaml']

# Push the image.
images: ['gcr.io/$PROJECT_ID/image']

Running File Tests Without Docker

Container images can be represented in multiple formats, and the Docker image is just one of them. At their core, images are just a series of layers, each of which is a tarball, and so can be interacted with without a working Docker daemon. While running command tests currently requires a functioning Docker daemon on the host machine, File Existence/Content tests do not. This can be particularly useful when dealing with images which have been docker exported or saved in a different image format than the Docker format. To run tests without using a Docker daemon, a user can specify a different "driver" to use in the tests, with the -driver flag.

An example test run with a different driver looks like:

./structure-test -driver tar -image gcr.io/google-appengine/python \
python_test_config.yaml

The currently supported drivers in the framework are:

  • docker: the default driver. Supports all tests, and uses the Docker daemon on the host to run them.
  • tar: a tar driver, which converts an image to a single tarball before interacting with it. Does not support command tests.

Running Structure Tests Through Bazel

Structure tests can also be run through bazel. To do so, load the rule and its dependencies in your WORKSPACE:

git_repository(
    name = "io_bazel_rules_docker",
    commit = "8aeab63328a82fdb8e8eb12f677a4e5ce6b183b1",
    remote = "https://github.com/bazelbuild/rules_docker.git",
)

load(
    "@io_bazel_rules_docker//container:container.bzl",
    "repositories",
)
repositories()


load(
    "@io_bazel_rules_docker//contrib:test.bzl",
    "container_test",
)

# io_bazel_rules_go is the dependency of container_test rules.
http_archive(
    name = "io_bazel_rules_go",
    url = "https://github.com/bazelbuild/rules_go/releases/download/0.9.0/rules_go-0.9.0.tar.gz",
    sha256 = "4d8d6244320dd751590f9100cf39fd7a4b75cd901e1f3ffdfd6f048328883695",
)
load("@io_bazel_rules_go//go:def.bzl", "go_rules_dependencies", "go_register_toolchains")
go_rules_dependencies()
go_register_toolchains()

and then include the rule definition in your BUILD file:

load("@io_bazel_rules_docker//contrib:test.bzl", "container_test")

Then, create a container_test rule, passing in your image and config file as parameters:

container_build(
    name = "hello",
    base = "//java:java8",
    cmd = ["/HelloJava_deploy.jar"],
    files = [":HelloJava_deploy.jar"],
)


container_test(
    name = "hello_test",
    configs = ["testdata/hello.yaml"],
    image = ":hello",
)

See this example repo for a full working example.