feat: add example extension hello world service

This is just an example of a system extension providing Talos extension
service.

Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>

Makefile

@@ -19,7 +19,7 @@ COMMON_ARGS += --build-arg=https_proxy=$(https_proxy)
 empty :=
 space = $(empty) $(empty)
 
-TARGETS = amd-ucode bnx2-bnx2x gvisor intel-ucode
+TARGETS = amd-ucode bnx2-bnx2x gvisor hello-world-service intel-ucode
 NONFREE_TARGETS =
 
 all: $(TARGETS) ## Builds all known pkgs.

examples/hello-world-service/README.md

@@ -0,0 +1,70 @@
+# Example Talos Extension Service
+
+This repository is an example of an extension service.
+
+## Usage
+
+Enable the extension in the machine configuration before installing Talos:
+
+```yaml
+machine:
+  install:
+    extensions:
+      - image: ghcr.io/talos-systems/hello-world-service:<VERSION>
+```
+
+Once this example extension is installed, it will provide simple HTTP server which responds with a message on port 80:
+
+```bash
+$ curl http://<IP>/
+Hello from Talos Linux Extension Service!
+```
+
+Extension service appears in the service list (please note the `ext-` prefix):
+
+```bash
+$ talosctl services
+NODE         SERVICE           STATE     HEALTH   LAST CHANGE   LAST EVENT
+172.20.0.5   apid              Running   OK       1m37s ago     Health check successful
+172.20.0.5   containerd        Running   OK       1m38s ago     Health check successful
+172.20.0.5   cri               Running   OK       1m37s ago     Health check successful
+172.20.0.5   ext-hello-world   Running   ?        1m38s ago     Started task ext-hello-world (PID 1100) for container ext-hello-world
+172.20.0.5   kubelet           Running   OK       1m30s ago     Health check successful
+172.20.0.5   machined          Running   ?        1m40s ago     Service started as goroutine
+172.20.0.5   udevd             Running   OK       1m38s ago     Health check successful
+```
+
+Run `talosctl service ext-hello-world` to see the detailed service state:
+
+```bash
+$ talosctl service ext-hello-world
+NODE     172.20.0.5
+ID       ext-hello-world
+STATE    Running
+HEALTH   ?
+EVENTS   [Running]: Started task ext-hello-world (PID 1100) for container ext-hello-world (2m47s ago)
+         [Preparing]: Creating service runner (2m47s ago)
+         [Preparing]: Running pre state (2m47s ago)
+         [Waiting]: Waiting for service "containerd" to be "up" (2m48s ago)
+         [Waiting]: Waiting for service "containerd" to be "up", network (2m49s ago)
+```
+
+The service can be started and stopped via `talosctl`:
+
+```bash
+$ talosctl  service ext-hello-world stop
+NODE         RESPONSE
+172.20.0.5   Service "ext-hello-world" stopped
+$ talosctl service ext-hello-world start
+NODE         RESPONSE
+172.20.0.5   Service "ext-hello-world" started
+```
+
+Use `talosctl logs` to access service logs:
+
+```bash
+$ talosctl logs ext-hello-world
+172.20.0.5: 2022/02/16 18:45:21 starting the hello world service
+172.20.0.5: 2022/02/16 18:52:33 stopping the hello world service
+172.20.0.5: 2022/02/16 18:52:35 starting the hello world service
+```

examples/hello-world-service/hello-world.yaml

@@ -0,0 +1,10 @@
+name: hello-world
+container:
+  entrypoint: ./hello-world
+  args:
+    - --msg
+    - Talos Linux Extension Service
+depends:
+  - network:
+    - addresses
+restart: always

examples/hello-world-service/manifest.yaml

@@ -0,0 +1,10 @@
+version: v1alpha1
+metadata:
+  name: hello-world-service
+  version: v1.0.0
+  author: Andrey Smirnov
+  description: |
+    This system extension provides an example Talos extension service.
+  compatibility:
+    talos:
+      version: "> v0.15.0-alpha.2"

examples/hello-world-service/pkg.yaml

@@ -0,0 +1,29 @@
+name: hello-world-service
+variant: scratch
+shell: /toolchain/bin/bash
+dependencies:
+  - stage: base
+steps:
+  - env:
+      GOPATH: /go
+    prepare:
+      - |
+    build:
+      - |
+        export PATH=${PATH}:${TOOLCHAIN}/go/bin
+
+        cd /pkg/src
+        CGO_ENABLED=0 go build -o ./hello-world .
+    install:
+      - |
+        mkdir -p /rootfs/usr/local/etc/containers
+        mkdir -p /rootfs/usr/local/lib/containers/hello-world
+
+        cp -p /pkg/src/hello-world /rootfs/usr/local/lib/containers/hello-world/
+finalize:
+  - from: /rootfs
+    to: /rootfs
+  - from: /pkg/manifest.yaml
+    to: /
+  - from: /pkg/hello-world.yaml
+    to: /rootfs/usr/local/etc/containers

examples/hello-world-service/src/go.mod

@@ -0,0 +1,3 @@
+module github.com/talos-systems/hello-world
+
+go 1.17

examples/hello-world-service/src/main.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+)
+
+var msg string
+
+func main() {
+	flag.StringVar(&msg, "msg", "", "hello message")
+	flag.Parse()
+
+	log.Printf("starting the hello world service")
+	defer log.Printf("stopping the hello world service")
+
+	done := make(chan os.Signal, 1)
+	signal.Notify(done, os.Interrupt, syscall.SIGINT, syscall.SIGTERM)
+
+	router := http.NewServeMux()
+	router.HandleFunc("/", HelloServer)
+
+	srv := &http.Server{
+		Addr:    ":80",
+		Handler: router,
+	}
+
+	go func() {
+		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+			log.Fatalf("listen error: %s", err)
+		}
+	}()
+
+	<-done
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := srv.Shutdown(ctx); err != nil {
+		log.Fatalf("server shutdown failed: %s", err)
+	}
+}
+
+func HelloServer(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "Hello from %s!", msg)
+}