doc: update quickstart guide to download latest artifacts

We need to manually change what versions our quick start guide points to
at every release. To avoid it getting behind, this change adds automatic
detection of the CI artifacts related to the lastest version (which was
already automatically detected).

This means that CI artifacts will not point to the latest available but
they will be the same we use to test the latest release, to ensure
compatibility and that the guide always works.

Signed-off-by: Riccardo Mancini <[email protected]>

Author: Manciukic

docs/getting-started.md

@@ -94,29 +94,44 @@ For simplicity, this guide will not use the [`jailer`](../src/jailer/).
 ### Getting a rootfs and Guest Kernel Image
 
 To successfully start a microVM, you will need an uncompressed Linux kernel
-binary, and an ext4 file system image (to use as rootfs). This guide uses a 5.10
-kernel image with a Ubuntu 24.04 rootfs from our CI:
+binary, and an ext4 file system image (to use as rootfs). This guide uses the
+latest kernel image and Ubuntu rootfs available in our CI for the latest
+release.
 
 ```bash
 ARCH="$(uname -m)"
-
-latest=$(wget "http://spec.ccfc.min.s3.amazonaws.com/?prefix=firecracker-ci/v1.11/$ARCH/vmlinux-5.10&list-type=2" -O - 2>/dev/null | grep -oP "(?<=<Key>)(firecracker-ci/v1.11/$ARCH/vmlinux-5\.10\.[0-9]{1,3})(?=</Key>)")
+release_url="https://github.com/firecracker-microvm/firecracker/releases"
+latest_version=$(basename $(curl -fsSLI -o /dev/null -w  %{url_effective} ${release_url}/latest))
+CI_VERSION=${latest_version%.*}
+latest_kernel_key=$(curl "http://spec.ccfc.min.s3.amazonaws.com/?prefix=firecracker-ci/$CI_VERSION/$ARCH/vmlinux-&list-type=2" \
+    | grep -oP "(?<=<Key>)(firecracker-ci/$CI_VERSION/$ARCH/vmlinux-[0-9]+\.[0-9]+\.[0-9]{1,3})(?=</Key>)" \
+    | sort -V | tail -1)
 
 # Download a linux kernel binary
-wget "https://s3.amazonaws.com/spec.ccfc.min/${latest}"
+wget "https://s3.amazonaws.com/spec.ccfc.min/${latest_kernel_key}"
+
+latest_ubuntu_key=$(curl "http://spec.ccfc.min.s3.amazonaws.com/?prefix=firecracker-ci/$CI_VERSION/$ARCH/ubuntu-&list-type=2" \
+    | grep -oP "(?<=<Key>)(firecracker-ci/$CI_VERSION/$ARCH/ubuntu-[0-9]+\.[0-9]+\.squashfs)(?=</Key>)" \
+    | sort -V | tail -1)
+ubuntu_version=$(basename $latest_ubuntu_key .sqashfs | grep -oE '[0-9]+\.[0-9]+')
 
 # Download a rootfs
-wget -O ubuntu-24.04.squashfs.upstream "https://s3.amazonaws.com/spec.ccfc.min/firecracker-ci/v1.11/${ARCH}/ubuntu-24.04.squashfs"
+wget -O ubuntu-$ubuntu_version.squashfs.upstream "https://s3.amazonaws.com/spec.ccfc.min/$latest_ubuntu_key"
 
 # Create an ssh key for the rootfs
-unsquashfs ubuntu-24.04.squashfs.upstream
+unsquashfs ubuntu-$ubuntu_version.squashfs.upstream
 ssh-keygen -f id_rsa -N ""
 cp -v id_rsa.pub squashfs-root/root/.ssh/authorized_keys
-mv -v id_rsa ./ubuntu-24.04.id_rsa
+mv -v id_rsa ./ubuntu-$ubuntu_version.id_rsa
 # create ext4 filesystem image
 sudo chown -R root:root squashfs-root
-truncate -s 400M ubuntu-24.04.ext4
-sudo mkfs.ext4 -d squashfs-root -F ubuntu-24.04.ext4
+truncate -s 400M ubuntu-$ubuntu_version.ext4
+sudo mkfs.ext4 -d squashfs-root -F ubuntu-$ubuntu_version.ext4
+
+# Verify everything was correctly set up and print versions
+echo "Kernel: $(ls vmlinux-* | tail -1)"
+echo "Rootfs: $(ls *.ext4 | tail -1)"
+echo "SSH Key: $(ls *.id_rsa | tail -1)"
 ```
 
 ### Getting a Firecracker Binary
@@ -241,7 +256,7 @@ sudo curl -X PUT --unix-socket "${API_SOCKET}" \
     }" \
     "http://localhost/boot-source"
 
-ROOTFS="./ubuntu-24.04.ext4"
+ROOTFS="./$(ls *.ext4 | tail -1)"
 
 # Set rootfs
 sudo curl -X PUT --unix-socket "${API_SOCKET}" \
@@ -282,14 +297,16 @@ sudo curl -X PUT --unix-socket "${API_SOCKET}" \
 # started before we attempt to SSH into it.
 sleep 2s
 
+KEY_NAME=./$(ls *.id_rsa | tail -1)
+
 # Setup internet access in the guest
-ssh -i ./ubuntu-24.04.id_rsa [email protected]  "ip route add default via 172.16.0.1 dev eth0"
+ssh -i $KEY_NAME [email protected]  "ip route add default via 172.16.0.1 dev eth0"
 
 # Setup DNS resolution in the guest
-ssh -i ./ubuntu-24.04.id_rsa [email protected]  "echo 'nameserver 8.8.8.8' > /etc/resolv.conf"
+ssh -i $KEY_NAME [email protected]  "echo 'nameserver 8.8.8.8' > /etc/resolv.conf"
 
 # SSH into the microVM
-ssh -i ./ubuntu-24.04.id_rsa [email protected]
+ssh -i $KEY_NAME [email protected]
 
 # Use `root` for both the login and password.
 # Run `reboot` to exit.