It is a special kind of program which runs as a aipeline of inter-connected computing nodes running in parallel, instead of a sequence of operations to be run by a single node.
DAGs are a powerful way to automate various parts of an application delivery workflow:
build, test, deploy, generate configuration, enforce policies, publish artifacts, etc.
The DAG architecture has many benefits:
- Because DAGs are made of nodes executing in parallel, they are easy to scale.
- Because all inputs and outputs are snapshotted and content-addressed, DAGs
can easily be made repeatable, can be cached aggressively, and can be replayed
at will.
- Because nodes are executed by the same container engine as docker-build, DAGs
can be developed using any language or technology capable of running in a docker.
Dockerfiles and docker images are natively supported for maximum compatibility.
- Because DAGs are programmed declaratively with a powerful configuration language,
they are much easier to test, debug and refactor than traditional programming languages.
To execute a DAG, the dagger runtime JIT-compiles it to a low-level format called llb, and executes it with buildkit. Think of buildkit as a specialized VM for running compute graphs; and dagger as a complete programming environment for that VM.
The tradeoff for all those wonderful features is that a DAG architecture cannot be used for all software: only software than can be run as a pipeline.
