Include meta data as labels in Dockerfile output

Summary:
Certain meta data including the Blubber version and variant used at
invocation may be useful in downstream tracking.

Implemented abstract and Docker-specific instructions for labels and
modified the Docker compiler to include these instructions at the end of
the output for the final stage.

Depends on D816
Fixes T178022

Test Plan:
Run unit tests. Run `make && bin/blubber blubber.example.yaml production` and
verify that both `blubber.version` and `blubber.variant` labels are present
and accurate.

Reviewers: thcipriani, hashar, #release-engineering-team

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Maniphest Tasks: T178022

Differential Revision: https://phabricator.wikimedia.org/D818

4 files changed, 75 insertions, 19 deletions

diff --git a/docker/compiler.go b/docker/compiler.go
index 79f179e..0a2120b 100644
--- a/docker/compiler.go
+++ b/docker/compiler.go
@@ -6,6 +6,7 @@ import (
 
 	"phabricator.wikimedia.org/source/blubber/build"
 	"phabricator.wikimedia.org/source/blubber/config"
+	"phabricator.wikimedia.org/source/blubber/meta"
 )
 
 // Compile blubber yaml file into Dockerfile
@@ -28,63 +29,73 @@ func Compile(cfg *config.Config, variant string) (*bytes.Buffer, error) {
 		if err != nil {
 			return nil, err
 		}
-		CompileStage(buffer, stage, dependency)
+		compileStage(buffer, stage, dependency)
 		mainStage = variant
 	}
 
-	CompileStage(buffer, mainStage, vcfg)
+	compileStage(buffer, mainStage, vcfg)
+
+	// add meta-data labels to the final stage
+	compileInstructions(buffer, build.Label{map[string]string{
+		"blubber.variant": variant,
+		"blubber.version": meta.FullVersion(),
+	}})
 
 	return buffer, nil
 }
 
-func CompileStage(buffer *bytes.Buffer, stage string, vcfg *config.VariantConfig) {
+func compileStage(buffer *bytes.Buffer, stage string, vcfg *config.VariantConfig) {
 	baseAndStage := vcfg.Base
 
 	if stage != "" {
 		baseAndStage += " AS " + stage
 	}
 
-	Writeln(buffer, "FROM ", baseAndStage)
+	writeln(buffer, "FROM ", baseAndStage)
 
-	Writeln(buffer, "USER root")
+	writeln(buffer, "USER root")
 
-	CompilePhase(buffer, vcfg, build.PhasePrivileged)
+	compilePhase(buffer, vcfg, build.PhasePrivileged)
 
 	if vcfg.Runs.As != "" {
-		Writeln(buffer, "USER ", vcfg.Runs.As)
+		writeln(buffer, "USER ", vcfg.Runs.As)
 	}
 
-	CompilePhase(buffer, vcfg, build.PhasePrivilegeDropped)
+	compilePhase(buffer, vcfg, build.PhasePrivilegeDropped)
 
 	if vcfg.Runs.In != "" {
-		Writeln(buffer, "WORKDIR ", vcfg.Runs.In)
+		writeln(buffer, "WORKDIR ", vcfg.Runs.In)
 	}
 
-	CompilePhase(buffer, vcfg, build.PhasePreInstall)
+	compilePhase(buffer, vcfg, build.PhasePreInstall)
 
-	CompilePhase(buffer, vcfg, build.PhaseInstall)
+	compilePhase(buffer, vcfg, build.PhaseInstall)
 
-	CompilePhase(buffer, vcfg, build.PhasePostInstall)
+	compilePhase(buffer, vcfg, build.PhasePostInstall)
 
 	if len(vcfg.EntryPoint) > 0 {
-		Writeln(buffer, "ENTRYPOINT [\"", strings.Join(vcfg.EntryPoint, "\", \""), "\"]")
+		writeln(buffer, "ENTRYPOINT [\"", strings.Join(vcfg.EntryPoint, "\", \""), "\"]")
 	}
 }
 
-func CompilePhase(buffer *bytes.Buffer, vcfg *config.VariantConfig, phase build.Phase) {
-	for _, instruction := range vcfg.InstructionsForPhase(phase) {
+func compileInstructions(buffer *bytes.Buffer, instructions ...build.Instruction) {
+	for _, instruction := range instructions {
 		dockerInstruction, _ := NewDockerInstruction(instruction)
-		Write(buffer, dockerInstruction.Compile())
+		write(buffer, dockerInstruction.Compile())
 	}
 }
 
-func Write(buffer *bytes.Buffer, strings ...string) {
+func compilePhase(buffer *bytes.Buffer, vcfg *config.VariantConfig, phase build.Phase) {
+	compileInstructions(buffer, vcfg.InstructionsForPhase(phase)...)
+}
+
+func write(buffer *bytes.Buffer, strings ...string) {
 	for _, str := range strings {
 		buffer.WriteString(str)
 	}
 }
 
-func Writeln(buffer *bytes.Buffer, strings ...string) {
-	Write(buffer, strings...)
+func writeln(buffer *bytes.Buffer, strings ...string) {
+	write(buffer, strings...)
 	buffer.WriteString("\n")
 }
diff --git a/docker/compiler_test.go b/docker/compiler_test.go
index 04454b4..846304b 100644
--- a/docker/compiler_test.go
+++ b/docker/compiler_test.go
@@ -8,6 +8,7 @@ import (
 
 	"phabricator.wikimedia.org/source/blubber/config"
 	"phabricator.wikimedia.org/source/blubber/docker"
+	"phabricator.wikimedia.org/source/blubber/meta"
 )
 
 func TestSingleStageHasNoName(t *testing.T) {
@@ -72,3 +73,21 @@ func TestMultipleArtifactsFromSameStage(t *testing.T) {
 	assert.Equal(t, 1, strings.Count(dockerfile, "FROM foo/bar AS build\n"))
 	assert.Equal(t, 1, strings.Count(dockerfile, "FROM foo/bar AS production\n"))
 }
+
+func TestMetaDataLabels(t *testing.T) {
+	cfg, err := config.ReadConfig([]byte(`---
+    base: foo/bar
+    variants:
+      development: {}`))
+
+	assert.Nil(t, err)
+
+	dockerOut, _ := docker.Compile(cfg, "development")
+	dockerfile := dockerOut.String()
+
+	version := meta.FullVersion()
+
+	assert.Contains(t, dockerfile,
+		"LABEL blubber.variant=\"development\" blubber.version=\""+version+"\"\n",
+	)
+}
diff --git a/docker/instructions.go b/docker/instructions.go
index fa566cb..eba6731 100644
--- a/docker/instructions.go
+++ b/docker/instructions.go
@@ -26,6 +26,10 @@ func NewDockerInstruction(instruction build.Instruction) (DockerInstruction, err
 		var dockerInstruction DockerEnv
 		dockerInstruction.arguments = instruction.Compile()
 		return dockerInstruction, nil
+	case build.Label:
+		var dockerInstruction DockerLabel
+		dockerInstruction.arguments = instruction.Compile()
+		return dockerInstruction, nil
 	case build.Volume:
 		var dockerInstruction DockerVolume
 		dockerInstruction.arguments = instruction.Compile()
@@ -81,6 +85,16 @@ func (de DockerEnv) Compile() string {
 		join(de.arguments, " "))
 }
 
+// DockerLabel represents a concrete LABEL instruction
+type DockerLabel struct{ abstractDockerInstruction }
+
+// Compile returns multiple key="value" arguments as a single LABEL string
+func (dl DockerLabel) Compile() string {
+	return fmt.Sprintf(
+		"LABEL %s\n",
+		join(dl.arguments, " "))
+}
+
 type DockerVolume struct{ abstractDockerInstruction }
 
 func (dv DockerVolume) Compile() string {
diff --git a/docker/instructions_test.go b/docker/instructions_test.go
index 87dfada..a4f648b 100644
--- a/docker/instructions_test.go
+++ b/docker/instructions_test.go
@@ -71,6 +71,18 @@ func TestEnv(t *testing.T) {
 	assert.Equal(t, "ENV bar=\"foo\" foo=\"bar\"\n", di.Compile())
 }
 
+func TestLabel(t *testing.T) {
+	i := build.Label{map[string]string{"foo": "bar", "bar": "foo"}}
+
+	di, err := docker.NewDockerInstruction(i)
+
+	var dockerLabel docker.DockerLabel
+
+	assert.Nil(t, err)
+	assert.IsType(t, dockerLabel, di)
+	assert.Equal(t, "LABEL bar=\"foo\" foo=\"bar\"\n", di.Compile())
+}
+
 func TestVolume(t *testing.T) {
 	i := build.Volume{"/foo/dir"}