Initial implementation. (#1)

.github/dependabot.yaml

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+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    open-pull-requests-limit: 5
+    schedule:
+      interval: 'weekly'
+      day: 'tuesday'
+  - package-ecosystem: 'gomod'
+    directory: '/'
+    schedule:
+      interval: 'weekly'
+      day: 'tuesday'
+    open-pull-requests-limit: 5

.github/workflows/build.yaml

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+name: Go
+
+on: [push]
+permissions:
+  contents: read
+  pull-requests: read
+  checks: write
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Go
+        uses: actions/setup-go@v4
+        with:
+          go-version-file: go.mod
+
+      - name: Verify
+        run: go mod verify
+
+      - name: Build
+        run: go build ./...
+
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v4
+        with:
+          version: latest
+          install-mode: binary
+
+      - name: Prepare manifests for linting
+        run: |
+          mkdir manifests
+          go run deploy/main.go my-images v0.0.8 vanilla > manifests/vanilla.yaml
+          go run deploy/main.go my-images v0.0.8 ocp > manifests/ocp.yaml
+          go run deploy/main.go my-images v0.0.8 vanilla my-secret > manifests/vanilla-with-secret.yaml
+          go run deploy/main.go my-images v0.0.8 ocp my-secret > manifests/ocp-with-secret.yaml
+
+      - name: kube-linter
+        uses: stackrox/kube-linter-action@v1.0.4
+        with:
+          directory: manifests

Dockerfile

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+FROM golang:1.22 AS builder
+LABEL authors="porridge@redhat.com"
+COPY . /image-prefetcher
+RUN cd /image-prefetcher && CGO_ENABLED=0 go build -a -ldflags '-extldflags "-static"' . && find . -ls
+
+FROM scratch
+COPY --from=builder /image-prefetcher/image-prefetcher /
+CMD ["image-prefetcher"]

README.md

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+# Image prefetcher
+
+This is a utility for quickly fetching OCI images onto Kubernetes cluster nodes.
+
+Talks directly to Container Runtime Interface ([CRI](https://kubernetes.io/docs/concepts/architecture/cri/)) API to:
+- fetch all images on all nodes in parallel,
+- retry pulls with increasingly longer timeouts. This prevents getting stuck on stalled connections to image registry.
+
+## Architecture
+
+### `image-prefetcher`
+
+- main binary,
+- meant to be run in pods of a DaemonSet,
+- shipped as an OCI image,
+- provides two subcommands:
+  - `fetch`: runs the actual image pulls via CRI, meant to run as an init container,
+    Requires access to the CRI UNIX domain socket from the host.
+  - `sleep`: just sleeps forever, meant to run as the main container,
+
+### `deploy`
+
+- a helper command-line utility for generating `image-prefetcher` manifests,
+- separate go module, with no dependencies outside Go standard library.
+
+## Usage
+
+1. First, run the `deploy` binary to generate a manifest for an instance of `image-prefetcher`.
+
+   You can run many instances independently.
+
+   It requires a few arguments:
+   - **name** of the instance.
+     This also determines the name of a `ConfigMap` supplying names of images to fetch.
+   - `image-prefetcher` OCI image **version**. See [list of existing tags](https://quay.io/repository/mowsiany/image-prefetcher?tab=tags).
+   - **cluster flavor**. Currently one of:
+     - `vanilla`: a generic Kubernetes distribution without additional restrictions.
+     - `ocp`: OpenShift, which requires explicitly granting special privileges.
+   - optional **image pull `Secret` name**. Required if the images are not pullable anonymously.
+     This image pull secret should be usable for all images fetched by the given instance.
+     If provided, it must be of type `kubernetes.io/dockerconfigjson` and exist in the same namespace.
+
+   Example:
+
+   ```
+   go run github.com/stackrox/image-prefetcher/deploy@main my-images v0.0.8 vanilla > manifest.yaml
+   ```
+
+2. Prepare an image list. This should be a plain text file with one image name per line.
+   Lines starting with `#` and blank ones are ignored.
+   ```
+   echo debian:latest >> image-list.txt
+   echo quay.io/strimzi/kafka:latest-kafka-3.7.0 >> image-list.txt
+   ```
+
+3. Deploy:
+   ```
+   kubectl create namespace prefetch-images
+   kubectl create -n prefetch-images configmap my-images --from-file="images.txt=image-list.txt"
+   kubectl apply -n prefetch-images -f manifest.yaml
+   ```
+
+4. Wait for the pull to complete, with a timeout:
+   ```
+   kubectl rollout -n prefetch-images status daemonset my-images --timeout 5m
+   ```
+
+5. If something goes wrong, look at logs:
+   ```
+   kubectl logs -n prefetch-images daemonset/my-images -c prefetch
+   ```
+
+### Customization
+
+You can tweak certain parameters such as timeouts by editing `args` in the above manifest.
+See the [fetch command](./cmd/fetch.go) for accepted flags.
+
+## Limitations
+
+This utility was designed for small, ephemeral test clusters, in order to improve reliability and speed of end-to-end tests.
+
+If deployed on larger clusters, it may have a "thundering herd" effect on the OCI registries it pulls from.
+This is because all images are pulled from all nodes in parallel.

cmd/fetch.go

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+package cmd
+
+import (
+	"log/slog"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/stackrox/image-prefetcher/internal"
+
+	"github.com/spf13/cobra"
+)
+
+// fetchCmd represents the fetch command
+var fetchCmd = &cobra.Command{
+	Use:   "fetch",
+	Short: "Fetch images using CRI.",
+	Long: `This subcommand is intended to run in an init container of pods of a DaemonSet.
+
+It talks to Container Runtime Interface API to pull images in parallel, with retries.`,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		opts := &slog.HandlerOptions{AddSource: true}
+		if debug {
+			opts.Level = slog.LevelDebug
+		}
+		logger := slog.New(slog.NewTextHandler(os.Stderr, opts))
+		timing := internal.TimingConfig{
+			ImageListTimeout:          imageListTimeout,
+			InitialPullAttemptTimeout: initialPullAttemptTimeout,
+			MaxPullAttemptTimeout:     maxPullAttemptTimeout,
+			OverallTimeout:            overallTimeout,
+			InitialPullAttemptDelay:   initialPullAttemptDelay,
+			MaxPullAttemptDelay:       maxPullAttemptDelay,
+		}
+		imageList, err := loadImageNamesFromFile(imageListFile)
+		if err != nil {
+			return err
+		}
+		imageList = append(imageList, args...)
+		return internal.Run(logger, criSocket, dockerConfigJSONPath, timing, imageList...)
+	},
+}
+
+var (
+	criSocket                 string
+	dockerConfigJSONPath      string
+	imageListFile             string
+	debug                     bool
+	imageListTimeout          = time.Minute
+	initialPullAttemptTimeout = 30 * time.Second
+	maxPullAttemptTimeout     = 5 * time.Minute
+	overallTimeout            = 20 * time.Minute
+	initialPullAttemptDelay   = time.Second
+	maxPullAttemptDelay       = 10 * time.Minute
+)
+
+func init() {
+	rootCmd.AddCommand(fetchCmd)
+
+	fetchCmd.Flags().StringVar(&criSocket, "cri-socket", "/run/containerd/containerd.sock", "Path to CRI UNIX socket.")
+	fetchCmd.Flags().StringVar(&dockerConfigJSONPath, "docker-config", "", "Path to docker config json file.")
+	fetchCmd.Flags().StringVar(&imageListFile, "image-list-file", "", "Path to text file containing images to pull (one per line).")
+	fetchCmd.Flags().BoolVar(&debug, "debug", false, "Whether to enable debug logging.")
+
+	fetchCmd.Flags().DurationVar(&imageListTimeout, "image-list-timeout", imageListTimeout, "Timeout for image list calls (for debugging).")
+	fetchCmd.Flags().DurationVar(&initialPullAttemptTimeout, "initial-pull-attempt-timeout", initialPullAttemptTimeout, "Timeout for initial image pull call. Each subsequent attempt doubles it until max.")
+	fetchCmd.Flags().DurationVar(&maxPullAttemptTimeout, "max-pull-attempt-timeout", maxPullAttemptTimeout, "Maximum timeout for image pull call.")
+	fetchCmd.Flags().DurationVar(&overallTimeout, "overall-timeout", overallTimeout, "Overall timeout for a single run.")
+	fetchCmd.Flags().DurationVar(&initialPullAttemptDelay, "initial-pull-attempt-delay", initialPullAttemptDelay, "Timeout for initial delay between pulls of the same image. Each subsequent attempt doubles it until max.")
+	fetchCmd.Flags().DurationVar(&maxPullAttemptDelay, "max-pull-attempt-delay", maxPullAttemptDelay, "Maximum delay between pulls of the same image.")
+}
+
+func loadImageNamesFromFile(fileName string) ([]string, error) {
+	if fileName == "" {
+		return nil, nil
+	}
+	bytes, err := os.ReadFile(fileName)
+	if err != nil {
+		return nil, err
+	}
+	return parseImageNames(bytes), nil
+}
+
+func parseImageNames(bytes []byte) []string {
+	var imageNames []string
+	for _, line := range strings.Split(string(bytes), "\n") {
+		line = strings.TrimSpace(line)
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		imageNames = append(imageNames, line)
+	}
+	return imageNames
+}

cmd/root.go

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+package cmd
+
+import (
+	"fmt"
+	"github.com/spf13/cobra"
+	"log"
+)
+
+// rootCmd represents the base command when called without any subcommands
+var rootCmd = &cobra.Command{
+	Use:   "image-prefetcher",
+	Short: "An image prefetching utility.",
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Println("Please use one of the subcommands. See --help")
+	},
+}
+
+// Execute is the entry point to this program.
+func Execute() {
+	if err := rootCmd.Execute(); err != nil {
+		log.Fatal(err)
+	}
+}

cmd/sleep.go

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+package cmd
+
+import (
+	"github.com/spf13/cobra"
+	"os"
+	"os/signal"
+	"syscall"
+)
+
+// sleepCmd represents the sleep command
+var sleepCmd = &cobra.Command{
+	Use:   "sleep",
+	Short: "Sleep forever.",
+	Long:  `This can be used as main container of a DaemonSet to avoid having to pull another image.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		println("Sleeping...")
+		cancelChan := make(chan os.Signal, 1)
+		signal.Notify(cancelChan, syscall.SIGTERM, syscall.SIGINT)
+		s := <-cancelChan
+		println("Terminating due to", s)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(sleepCmd)
+}