Support locally built images with Docker::Image.get fallback in #start

Hi there 👋,

Thanks for the great work on testcontainers-ruby!

Currently, the #start method internally uses:

`Docker::Image.create(...)´

This approach always tries to pull the image from a remote registry, which can be problematic when I’ve built an image locally using:

image_name = "my-name:latest"
Docker::Image.build_from_dir('.', { "t" => image_name, "dockerfile" => "Dockerfile" })

n such cases, it would be helpful if #start could attempt to use Docker::Image.get(image_name) first to find a local image, and only fall back to Docker::Image.create(...) if it's not found.

Proposed logic:

begin
  image = Docker::Image.get(image_name)
rescue Docker::Error::NotFoundError
  image = Docker::Image.create('fromImage' => image_name)
end

Alternatively — or even better — maybe the project could support building an image natively from a local Dockerfile as part of the container lifecycle setup? This would make local development more seamless and reduce external dependencies for custom containers.

Would you be open to adding this fallback behavior?

Thanks again

Just to add some context — I tried working around this by monkey patching the #start method like so:

module TestcontainersExtensions
  refine Testcontainers::DockerContainer do
    def start_local_image
      @_container ||= Docker::Container.create(_container_create_options)
      @_container.start

      @_id = @_container.id
      json = @_container.json
      @name = json["Name"]
      @_created_at = json["Created"]

      @wait_for&.call(self)

      self
    rescue Docker::Error::NotFoundError => e
      raise NotFoundError, e.message
    rescue Excon::Error::Socket => e
      raise ConnectionError, e.message
    end
  end
end

using TestcontainersExtensions

@dieter-medium

maybe the project could support building an image natively from a local Dockerfile as part of the container lifecycle setup? This would make local development more seamless and reduce external dependencies for custom containers.

@dieter-medium That's part of our roadmap, can you create a PR for it? If a different API is needed for this we can see to other testcontainers projects for inspiration about how the API would be.

@dieter-medium

@dieter-medium see #92

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Support locally built images with Docker::Image.get fallback in #start #78

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Support locally built images with Docker::Image.get fallback in #start #78

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dieter-medium commented on Apr 6, 2025

guilleiguaran commented on May 7, 2025

guilleiguaran commented on Oct 19, 2025

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