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.
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
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
To use container structure tests to validate your containers, you'll need the following:
- The container structure test binary or docker image
- A container image to test against
- A test
.jsonfile 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.
An example run of the test framework:
container-structure-test test --image gcr.io/registry/image:latest \ --config config.yaml
Tests within this framework are specified through a YAML or JSON config file, which is provided to the test driver via a CLI flag. 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 ensure that certain commands run properly in the target image.
Regexes can be used to check for expected or excluded strings in both
stderr. Additionally, any number of flags can be passed to the argument
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.
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.*"]
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
commandTests: ... setup: [["my_image_entrypoint.sh"]] ...
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.
- 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
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.
- 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
fileContentTests: - name: 'Debian Sources' path: '/etc/apt/sources.list' expectedContents: ['.*httpredir\.debian\.org.*'] excludedContents: ['.*gce_debian_mirror.*']
The Metadata test ensures the container is configured correctly. All of these checks are optional.
- 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.
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 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.
- 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.
licenseTests: - debian: true files: ["/foo/bar", "/baz/bat"]
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"
This tool is released as a builder image, tagged as
gcr.io/gcp-runtimes/container-structure-test, so you can specify tests in your
steps: # Build an image. - name: 'gcr.io/cloud-builders/docker' args: ['build', '-t', 'gcr.io/$PROJECT_ID/image', '.'] # Test the image. - name: 'gcr.io/gcp-runtimes/container-structure-test' args: ['test', '--image', 'gcr.io/$PROJECT_ID/image', '--config', '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
useful when dealing with images which have been
or saved in a different image format than the Docker format, or when you're simply
trying to run structure tests in an environment where Docker can't be installed.
To run tests without using a Docker daemon, users can specify a different
"driver" to use in the tests, with the
An example test run with a different driver looks like:
container-structure-test test --driver tar --image gcr.io/registry/image:latest \ --config 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 extracts an image filesystem to wherever tests are running, and runs file/metadata tests against it. Does not support command tests.
Running Structure Tests Through Bazel
Structure tests can also be run through
To do so, load the rule and its dependencies in your
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
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.