Part 2: Executing a build
In the example we walked through in part 1, we can see two explicit targets: build and docker. In order to execute the build, we can run, for example:
earthly +build
or
earthly +docker
The output might look like this:
Notice how to the left of |, within the output, we can see some targets like +base, +build and +docker . Notice how the output is interleaved between +docker and +build. This is because the system executes independent build steps in parallel. The reason this is possible effortlessly is because only very few things are shared between the builds of the recipes and those things are declared and obvious. The rest is completely isolated.
In addition, notice how even though the base is used as part of both build and docker, it is only executed once. This is because the system deduplicates execution, where possible.
Furthermore, the fact that the docker target depends on the build target is visible within the command COPY +build/.... Through this command, the system knows that it also needs to build the target +build, in order to satisfy the dependency on the artifact.
Finally, notice how the output of the build (the docker image and the files) are only written after the build is declared a success. This is due to another isolation principle of Earthly: a build either succeeds completely or it fails altogether.
Once the build has executed, we can run the resulting docker image to try it out:
$ docker run --rm go-example:latesthello world
$ docker run --rm js-example:latesthello world
$ docker run --rm java-example:latesthello world
$ docker run --rm python-example:latesthello world
Targets have a particular referencing convention which helps Earthly to identify which recipe to execute. In the simplest form, targets are referenced by +<target-name>. For example, +build. For more details see the target referencing page.
