DockerAvailability

DockerAvailability is a small Elixir library for checking whether Docker is installed and usable from the current host process.

It checks more than the presence of the docker command. A host may have the Docker CLI installed while the Docker daemon is stopped, unreachable, or inaccessible to the current user. DockerAvailability probes both the Docker client and the Docker server so callers can fail early with clear diagnostics.

Installation

When the package is published to Hex, add docker_availability to your list of dependencies in mix.exs:

def deps do
  [
    {:docker_availability, "~> 1.0.0"}
  ]
end

During development, you can also depend on this repository directly:

def deps do
  [
    {:docker_availability,
     github: "zacky1972/docker_availablility",
     branch: "main"}
  ]
end

Then fetch dependencies:

mix deps.get

Usage

Use available?/0 when you only need a boolean answer:

if DockerAvailability.available?() do
  IO.puts("Docker is available")
else
  IO.puts("Docker is not available")
end

Use check/0 when you need diagnostic details:

case DockerAvailability.check() do
  {:ok, info} ->
    IO.puts("Docker executable: #{info.executable}")
    IO.puts("Docker client: #{info.client_version}")
    IO.puts("Docker server: #{info.server_version}")

  {:error, :docker_not_found} ->
    IO.puts("The docker executable was not found in PATH")

  {:error, {:docker_command_failed, status, output}} ->
    IO.puts("Docker client command failed with status #{status}")
    IO.puts(output)

  {:error, {:docker_unavailable, status, output}} ->
    IO.puts("Docker daemon is not available with status #{status}")
    IO.puts(output)
end

Use executable/0 when you only need to know whether the docker executable exists in PATH:

DockerAvailability.executable()
#=> {:ok, "/usr/bin/docker"}

DockerAvailability.executable()
#=> {:error, :docker_not_found}

API

DockerAvailability.executable/0

Returns the path to the docker executable.

It only checks the current process PATH by using System.find_executable/1. It does not check whether the Docker daemon is running.

Returns:

• {:ok, path} when the executable is found
• {:error, :docker_not_found} when the executable is not available in PATH

DockerAvailability.available?/0

Returns true when Docker is installed and usable by the current process.

This is a convenience wrapper around check/0. It returns false for all error cases, including a missing executable, a failed Docker client command, or an unreachable Docker daemon.

DockerAvailability.check/0

Performs the full availability check.

It verifies that:

1. the docker executable exists in PATH
2. the Docker client version can be queried
3. the Docker server version can be queried

Returns {:ok, info} when Docker is usable. The info map contains:

• :executable - the resolved path to the Docker executable
• :client_version - the Docker client version reported by the executable
• :server_version - the Docker server version reported by the daemon

Returns one of the following errors:

• {:error, :docker_not_found} when docker is not found in PATH
• {:error, {:docker_command_failed, status, output}} when a Docker client command fails before daemon availability is established
• {:error, {:docker_unavailable, status, output}} when the Docker server version cannot be queried

status is the command exit status. output is the trimmed combined standard output and standard error from the Docker command.

What this library does not do

DockerAvailability is a probe only. It does not:

• install Docker
• start or stop the Docker daemon
• pull, build, run, or remove Docker images or containers
• modify Docker state
• require a specific Docker image

Examples

A common use case is to skip Docker-dependent work when Docker is not available:

case DockerAvailability.check() do
  {:ok, _info} ->
    run_docker_dependent_work()

  {:error, reason} ->
    {:skip, {:docker_unavailable, reason}}
end

For test suites, available?/0 can be used to guard integration tests:

setup_all do
  unless DockerAvailability.available?() do
    ExUnit.configure(exclude: [:docker])
  end

  :ok
end

Testing

Run the test suite with:

mix test

The unit tests use a fake docker executable placed in a temporary PATH, so they do not require a real Docker daemon or any Docker image.

Development

Fetch dependencies:

mix deps.get

Run tests:

mix test

Run the project checks:

mix check

Run the maintainer pre-commit checks:

mix precommit

Documentation

Generate documentation locally with:

mix docs

After the package is published, documentation should be available on HexDocs.

Requirements

• Elixir ~> 1.19
• Docker CLI and daemon, when checking real Docker availability at runtime

License

Apache-2.0. See LICENSE.md.