Download binaries needed for airgapped K3S install

download-k3s-airgap-images.sh

#!/usr/bin/env bash
#
# Usage:
#   ./download-k3s-airgap-images.sh [K3S_RELEASE_TAG] [ARCH]
#
# Examples:
#   # Download for the latest stable release, auto-detect arch
#   ./download-k3s-airgap-images.sh
#
#   # Download for a specific release and architecture
#   ./download-k3s-airgap-images.sh v1.26.2+k3s1 arm64
#
# Notes:
#   - This script uses the GitHub API to detect the latest stable release.
#   - It downloads the .tar.zst file and the associated sha256sum.
#   - It then verifies the sha256sum.

set -euo pipefail

# Optional: specify a release tag (e.g. "v1.26.2+k3s1").
# If none is provided, 'latest' is used, which triggers detection of the latest stable release.
K3S_RELEASE="${1:-latest}"

# Optional: specify an architecture. If none is provided, we'll detect it from uname -m.
# Common valid K3s arches: amd64, arm64, armhf
ARCH="${2:-$(uname -m)}"

# Convert uname architecture to K3s naming if needed
case "$ARCH" in
  x86_64)
    ARCH="amd64"
    ;;
  aarch64)
    ARCH="arm64"
    ;;
  armv7l)
    ARCH="arm"
    ;;
esac

# -- Choose the binary name based on architecture --
#    - amd64  -> k3s
#    - arm64  -> k3s-arm64
#    - armhf  -> k3s-armhf
case "$ARCH" in
  amd64)
    BINARY_NAME="k3s"
    ;;
  arm64)
    BINARY_NAME="k3s-arm64"
    ;;
  arm)
    BINARY_NAME="k3s-armhf"
    ;;
  *)
    echo "Unsupported or unknown architecture: $ARCH"
    exit 1
    ;;
esac

# Function to get the latest stable (non-pre-release) K3s version from GitHub
get_latest_stable_release() {
  # Pull all releases, filter out pre-releases and drafts, sort by version, take the latest.
  curl -s https://api.github.com/repos/k3s-io/k3s/releases \
  | jq -r '.[] | select(.prerelease == false and .draft == false) | .tag_name' \
  | sort -rV \
  | head -n1
}

# If 'latest' was specified, we pull the latest stable release from the API
if [ "$K3S_RELEASE" == "latest" ]; then
  echo "No release specified, finding the latest stable K3s release..."
  K3S_RELEASE="$(get_latest_stable_release)"
  if [ -z "$K3S_RELEASE" ]; then
    echo "Error: Could not determine the latest stable release from GitHub."
    exit 1
  fi
  echo "Latest stable K3s release is: $K3S_RELEASE"
fi

# Construct the file name based on the chosen release and architecture
IMAGE_FILENAME="k3s-airgap-images-${ARCH}.tar.gz"
K3S_URL="https://github.com/k3s-io/k3s/releases/download/${K3S_RELEASE}/${BINARY_NAME}"
DOWNLOAD_URL="https://github.com/k3s-io/k3s/releases/download/${K3S_RELEASE}/${IMAGE_FILENAME}"
SHA256_URL="https://github.com/k3s-io/k3s/releases/download/${K3S_RELEASE}/sha256sum-${ARCH}.txt"


echo "-----------------------------------------------------"
echo "K3S Release:  $K3S_RELEASE"
echo "Architecture: $ARCH"
echo "Image file:   $IMAGE_FILENAME"
echo "Download URL: $DOWNLOAD_URL"
echo "Download K3S: $K3S_URL"
echo "Checksum URL: $SHA256_URL"
echo "-----------------------------------------------------"

# Download the airgap image tar.zst
echo "Downloading airgap image..."
curl -fSL -O "${DOWNLOAD_URL}"

# Download the k3s binary
echo "Downloading k3s binary..."
curl -fSL -O "${K3S_URL}"

# Download the sha256sum file
echo "Downloading airgap image sha256sum..."
curl -fSL -O "${SHA256_URL}"


# Extract used checksums
grep gz sha256sum-${ARCH}.txt > sha256sum-gz.txt
grep "${BINARY_NAME}$" sha256sum-${ARCH}.txt > sha256sum-k3s.txt

# Validate the downloaded images file
echo "Validating images checksum..."
sha256sum -c "sha256sum-gz.txt"

# Validate the downloaded k3s file
echo "Validating k3s checksum..."
sha256sum -c "sha256sum-k3s.txt"

echo "-----------------------------------------------------"
echo "Download and validation complete!"
echo "You now have ${IMAGE_FILENAME} (and its verified checksum)."
echo "Use this file for your air-gapped K3s installation."
echo "-----------------------------------------------------"