Frequently Asked Questions
How is Earthly different from Dockerfiles?¶
Dockerfiles were designed for specifying the make-up of Docker images and that’s where Dockerfiles stop. Earthly takes some key principles of Dockerfiles (like layer caching), but expands on the use-cases. For example, Earthly can output regular artifacts, run unit and integration tests, and create several Docker images at a time - all outside the scope of Dockerfiles.
Earthly introduces a richer target, artifact, and image referencing system, allowing for better reuse in complex builds spanning a single large repository or multiple repositories. Because Dockerfiles are only meant to describe one image at a time, such features are outside the scope of applicability of Dockerfiles.
Why not just use docker and bash/make/python/ruby/etc?¶
Sure, you can do that. That’s how earthly started.
Earthly grew out of a wrapper around Dockerfiles. As your project grows, your build and testing requirements will grow too. You might end up with multiple Dockerfiles, you might need to support running tests and builds on both Linux, MacOS, and Windows, you might run into parallelisation issues, you might need to scale across multiple repositories. Earthly grew out of all of these requirements and is supported by a growing user-base, which (most likely) offers a more battle-tested code-base than your custom in-house wrapper.
Still think you should just write your own wrapper? We have some tips on our blog.
Is Earthly a way to define a Docker multi-stage build?¶
Yes, that is one of its uses.
Docker Multi-stage builds can get complex and hard to follow as they accumulate steps. The target syntax of earthly is easier to understand.
However Earthly is not only a tool for producing docker containers. Earthly is a tool for building cross platform build specifications. It can produce docker images but it can also be used to produce binary artifacts, to run tests, to lint code, and anything else you would normally do inside of build pipeline in Jenkins, GitHub Actions, Travis CI or your-continous-integration-system-of-choice.
Can I use Earthly with my continuous integration system?¶
Yes, if you install Earthly where your builds run, then you can use Earthly with your continuous integration system. We have documented integrations for some popular CI systems but it is likely that you will be able to get earthly working with your existing CI System. Hop in our Slack channel and you may find others using your CI system of choice.
Can I use Earthly with my programming language or command line build tools?¶
Yes. If it’s possible to create a docker image with your programming language, compiler, and tools of choice installed then its possible to use these with Earthly.
Earthly is especially popular with those who need to work with several languages or tools in a single build pipeline. Earthly can act as a glue layer that holds the various tools together and provides caching and parallelism across them.
Can Earthly build Dockerfiles?¶
Yes! You can use the command
FROM DOCKERFILE to inherit the commands in an existing Dockerfile.
build: FROM DOCKERFILE . SAVE IMAGE some-image:latest
You may also optionally port your Dockerfiles to Earthly entirely. Translating Dockerfiles to Earthfiles is usually a matter of copy-pasting and making minor adjustments. See the getting started page for some Earthfile examples.
How does Earthly compare to Nix?¶
Both Nix and Earthly are focusing on improving the way that software is built but we believe they have different goals.
At a technical level, both Nix and Earthly use Linux namespaces to provide file system isolation. Earthly uses namespaces via Runc, using BuildKit whereas Nix uses them directly.
At a higher level, though, Earthly is focused on providing an easy to write language for declaring all the steps of a complex build pipeline. This often includes things that may not be a good fit of the Nix build model, such as code linting, starting up and tearing down dependent services, making network calls and running integration tests.
How is Earthly different from Bazel?¶
Bazel is a build tool developed by Google to optimize the speed, correctness, and reproducibility of their internal monorepo codebase. The main difference between Bazel and Earthly is that Bazel is a build system, whereas Earthly is a general-purpose CI/CD framework.
Bazel focuses on compiling and unit testing, and it does so in a highly opinionated manner. Bazel is an extremely efficient build system that provides speed, correctness, and reproducibility. But Bazel is difficult to adopt, and you have to implement it correctly to get its benefits. Achieving anything beyond compiling and unit testing is difficult and time-consuming.
Earthly, on the other hand, can be used for general-purpose CI/CD use cases. Earthly can compile and run unit tests like Bazel, but, it goes beyond that, allowing integration testing, deployment to production, executing arbitrary scripts, performing custom packaging, etc.
Bazel does exceptionally well in very specific environments, for very specific use cases, but it is not a general-purpose CI/CD framework.
For these reasons, Bazel is often run in conjunction with Earthly, rather than instead of it. Here is an example of how to do that in the Earthly repository on GitHub. In particular, the combination of Bazel and Earthly Satellites (or self-hosted Earthly remote runners) allows Bazel’s cache to be saved on the remote runner and be instantly available on the next build. This can make Bazel executions in CI very fast.
One of Bazel’s use cases is managing builds for a monorepo setup. For this use case, there is some overlap with what Earthly can do. Here are some key differences between the two:
- Earthly is significantly easier to adopt. Every new programming language that Bazel needs to build requires onboarding, and all build files usually need to be completely rewritten. This can be a significant investment of time and effort from the team adopting it. For large codebases, migration often takes a few years. Earthly, on the other hand, does not replace language-specific tools. This makes migrating to Earthly much faster and easier, only taking a few weeks to a few months.
- The learning curve of Earthly is much lower than Bazel. Learning Earthly is especially easy if you already have experience with Dockerfiles. Bazel, on the other hand, introduces several new concepts and a custom programming language. The difficulty of learning how to use Bazel means fewer engineers across a team will be able to use it. Earthly’s simplicity makes it easier to democratize builds across a team than with Bazel.
- Bazel has a purely descriptive specification language. Earthly is a mix of descriptive and imperative language.
- Earthly does not do file-level compilation caching on its own. Bazel does. So incremental compilation of large codebases is faster on Bazel. You can set up Earthly to cache individually compiled files, but that requires more work (we’re working to improve this).
- Bazel’s consistency is more correct and more difficult to achieve, while Earthly’s consistency is more practical. Bazel uses tight control of compiler toolchains to achieve true hermetic builds, whereas Earthly uses containers and well-defined inputs. Bazel achieves truly reproducible builds – the output is byte-for-byte consistent across systems – when run in hermetic environments (compiler versions match, dependencies match, etc.). Earthly achieves repeatable builds – consistency is guaranteed by using containers to ensure that the build executes in a similar environment. The build output is usually not byte-for-byte the same except under specific situations (e.g. dependencies are pinned to fixed versions, compilers used in the build don’t introduce timestamps, etc.).
For more information about when to use Bazel, check out our blog, where we have written an extensive article on the topic.
How is Earthly different from Dagger?¶
Both Dagger and Earthly are open-source CI/CD frameworks that use BuildKit and containerization to improve the CI workflow. With both tools you can run the CI or CD process locally, which is a big step forward from the world of needing to work with a centralized build process.
The most significant difference between Earthly and Dagger is the way a build process is specified:
- Earthly uses an
Earthfileto specify a build in a format that takes inspiration from Dockerfiles, shell scripting, and Makefiles. As a result, if you know how to perform a step in your build process at the command line, you know how to do it in Earthly.
- Dagger uses a configuration language to configure build steps. The configuration language is CUE – a language that extends YAML with concepts such as types, constraints, and packages.
This difference means Earthly is more accessible to both experienced, and first-time users. Many users can understand and make simple changes to Earthfiles without reading any documentation. On the other hand, Dagger can require a considerable learning investment. This investment can pay off: there are forms of abstraction available in Dagger (Value Constraints for instance), which are harder to encode in Earthly. If you need those features, Dagger might be a great choice.
But overall, we believe Earthly’s strong focus on approachability and ease of first-time use is a fantastic match for most organizations.