142 lines
4.3 KiB
Markdown
142 lines
4.3 KiB
Markdown
---
|
|
slug: /1221/action
|
|
displayed_sidebar: '0.2'
|
|
---
|
|
|
|
# Dagger Actions
|
|
|
|
Actions are the basic building block of the Dagger platform.
|
|
An action encapsulates an arbitrarily complex automation into a simple
|
|
software component that can be safely shared, and repeatably executed by any Dagger engine.
|
|
|
|
Actions can be executed directly with `dagger do`, or integrated as a component of a more complex action.
|
|
|
|
There are two types of actions: _core actions_ and _composite actions_.
|
|
|
|
## Core Actions
|
|
|
|
Core Actions are primitives implemented by the Dagger Engine itself. They can be combined into higher-level composite actions. Their definitions can be imported in the `dagger.io/dagger/core` package.
|
|
|
|
To learn more about core actions, see [the core action reference](https://github.com/dagger/dagger/tree/main/pkg/dagger.io/dagger/core).
|
|
|
|
## Composite Actions
|
|
|
|
Composite Actions are actions made of other actions. Dagger supports arbitrary nesting of actions, so a composite action can be assembled from any combination of core and composite actions.
|
|
|
|
One consequence of arbitrary nesting is that Dagger doesn't need to distinguish between "pipelines" and "steps": everything is an action. Some actions are just more complex and powerful than others. This is a defining feature of Dagger.
|
|
|
|
## Lifecycle of an Action
|
|
|
|
A composite action's lifecycle has 4 stages:
|
|
|
|
1. Definition
|
|
2. Integration
|
|
3. Discovery
|
|
4. Execution
|
|
|
|
### Definition
|
|
|
|
A new action is _defined_ in a declarative template called a [CUE definition](https://cuetorials.com/overview/foundations/#definitions). This definition describes the action's inputs, outputs, sub-actions, and the wiring between them.
|
|
|
|
Here is an example of a simple action definition:
|
|
|
|
```cue
|
|
package main
|
|
|
|
import (
|
|
"dagger.io/dagger"
|
|
"dagger.io/dagger/core"
|
|
)
|
|
|
|
// Write a greeting to a file, and add it to a directory
|
|
#AddHello: {
|
|
// The input directory
|
|
dir: dagger.#FS
|
|
|
|
// The name of the person to greet
|
|
name: string | *"world"
|
|
|
|
write: core.#WriteFile & {
|
|
input: dir
|
|
path: "hello-\(name).txt"
|
|
contents: "hello, \(name)!"
|
|
}
|
|
|
|
// The directory with greeting message added
|
|
result: write.output
|
|
}
|
|
```
|
|
|
|
Note that this action includes one sub-action: `core.#WriteFile`. An action can incorporate any number of sub-actions.
|
|
|
|
Also note the free-form structure: an action definition is not structured by a rigid schema. It is simply a CUE struct with fields of various types.
|
|
|
|
- "inputs" are simply fields which are not complete, and therefore can receive an external value at integration. For example, `dir` and `name` are inputs.
|
|
- "outputs" are simply fields which produce a value that can be referenced externally at integration. For example, `result` is an output.
|
|
- "sub-actions" are simply fields which contain another action definition. For example, `write` is a sub-action.
|
|
|
|
There are no constraints to an action's field names or types.
|
|
|
|
### Integration
|
|
|
|
Action definitions cannot be executed directly: they must be integrated into a plan.
|
|
|
|
A plan is an execution context for actions. It specifies:
|
|
|
|
- What actions to present to the end user
|
|
- Dependencies between those tasks, if any
|
|
- Interactions between the tasks and the client system, if any
|
|
|
|
Actions are integrated into a plan by _merging_ their CUE definition into the plan's CUE definition.
|
|
|
|
Here is an example of a plan:
|
|
|
|
```cue
|
|
package main
|
|
|
|
import (
|
|
"dagger.io/dagger"
|
|
)
|
|
|
|
dagger.#Plan & {
|
|
// Say hello by writing to a file
|
|
actions: hello: #AddHello & {
|
|
dir: client.filesystem.".".read.contents
|
|
}
|
|
client: filesystem: ".": {
|
|
read: contents: dagger.#FS
|
|
write: contents: actions.hello.result
|
|
}
|
|
}
|
|
```
|
|
|
|
Note that `#AddHello` was integrated _directly_ into the plan, whereas `core.#WriteFile` was integrated _indirectly_, by virtue of being a sub-action of `#AddHello`.
|
|
|
|
To learn more about the structure of a plan, see [it all begins with a plan](./1202-plan.md).
|
|
|
|
### Discovery
|
|
|
|
Once integrated into a plan, actions can be discovered by end users, by using the familiar convention of usage messages:
|
|
|
|
```bash
|
|
$ dagger do --help
|
|
Execute a dagger action.
|
|
|
|
Available Actions:
|
|
hello Say hello by writing to a file
|
|
|
|
Usage:
|
|
dagger do [OPTIONS] ACTION [SUBACTION...] [flags]
|
|
|
|
Flags:
|
|
[...]
|
|
```
|
|
|
|
### Execution
|
|
|
|
Once the end user has discovered the action that they need, they can execute it with `dagger do`. For example:
|
|
|
|
```bash
|
|
dagger do hello
|
|
```
|