Add documentation for building container images

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

docs/core-concepts/1205-container-images.md

@@ -4,3 +4,41 @@ displayed_sidebar: europa
 ---
 
 # Building container images
+
+You can use Dagger to build container images. Here's a simple example of a [Dockerfile](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/) build:
+
+```cue file=../tests/core-concepts/container-images/plans/with-dockerfile.cue
+```
+
+## Building with CUE
+
+`Dockerfile` files are easy to start, but you can also build images entirely in CUE. The following example produces the same image as above:
+
+```cue file=../tests/core-concepts/container-images/plans/build.cue
+```
+
+## Automation
+
+Building images in CUE gives you greater flexibility. For example, you can automate building multiple versions of an image, and deploy, all in Dagger:
+
+```cue file=../tests/core-concepts/container-images/plans/template.cue
+```
+
+Now you can deploy all versions:
+
+```shell
+dagger do versions
+```
+
+Or just build a specific version, without pushing:
+
+```shell
+dagger do versions 8.0 build
+```
+
+## Multi-stage build
+
+Another common pattern is [multi-stage builds](https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds). This allows you to have heavier build images during the build process, and copy the built artifacts into a cleaner and lighter image to run in production.
+
+```cue file=../tests/core-concepts/container-images/plans/multi-stage.cue
+```

docs/tests/core-concepts/container-images/plans/build.cue

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"dagger.io/dagger"
+	"universe.dagger.io/docker"
+)
+
+dagger.#Plan & {
+	client: filesystem: ".": read: contents: dagger.#FS
+
+	actions: build: docker.#Build & {
+		steps: [
+			docker.#Pull & {
+				source: "python:3.9"
+			},
+			docker.#Copy & {
+				contents: client.filesystem.".".read.contents
+				dest:     "/app"
+			},
+			docker.#Run & {
+				command: {
+					name: "pip"
+					args: ["install", "-r", "/app/requirements.txt"]
+				}
+			},
+			docker.#Set & {
+				config: cmd: ["python", "/app/app.py"]
+			},
+		]
+	}
+}

docs/tests/core-concepts/container-images/plans/multi-stage.cue

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"dagger.io/dagger"
+	"universe.dagger.io/alpine"
+	"universe.dagger.io/docker"
+	"universe.dagger.io/go"
+)
+
+dagger.#Plan & {
+	client: filesystem: src: read: contents: dagger.#FS
+
+	actions: {
+		// Build app in a "golang" container image.
+		build: go.#Build & {
+			source: client.filesystem.src.read.contents
+		}
+
+		base: alpine.#Build & {
+			packages: "ca-certificates": _
+		}
+
+		// Build lighter image,
+		// without app's build dependencies.
+		run: docker.#Build & {
+			steps: [
+				docker.#Copy & {
+					input: base.output
+					// This is the important part, it works like
+					// `COPY --from=build /output /opt` in a Dockerfile.
+					contents: build.output
+					dest:     "/opt"
+				},
+				docker.#Set & {
+					config: cmd: ["/opt/app"]
+				},
+			]
+		}
+
+		push: docker.#Push & {
+			image: run.output
+			dest:  "registry.example.com/app"
+		}
+	}
+}

docs/tests/core-concepts/container-images/plans/template.cue

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"dagger.io/dagger"
+	"universe.dagger.io/docker"
+)
+
+dagger.#Plan & {
+	actions: versions: {
+		"8.0": _
+		"5.7": _
+
+		// This is a template
+		// See https://cuelang.org/docs/tutorials/tour/types/templates/
+		[tag=string]: {
+			build: docker.#Build & {
+				steps: [
+					docker.#Pull & {
+						source: "mysql:\(tag)"
+					},
+					docker.#Set & {
+						config: cmd: [
+							"--character-set-server=utf8mb4",
+							"--collation-server=utf8mb4_unicode_ci",
+						]
+					},
+				]
+			}
+			push: docker.#Push & {
+				image: build.output
+				dest:  "registry.example.com/mysql:\(tag)"
+			}
+		}
+	}
+}

docs/tests/core-concepts/container-images/plans/with-dockerfile.cue

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"dagger.io/dagger"
+)
+
+dagger.#Plan & {
+	client: filesystem: ".": read: contents: dagger.#FS
+
+	actions: build: dagger.#Dockerfile & {
+		// This is the context.
+		source: client.filesystem.".".read.contents
+
+		// Default is to look for a Dockerfile in the context,
+		// but let's declare it here.
+		contents: #"""
+			FROM python:3.9
+			COPY . /app
+			RUN pip install -r /app/requirements.txt
+			CMD python /app/app.py
+
+			"""#
+	}
+}