From cd6644ea4ddc78597934ab0ef5ba50e3c3daa927 Mon Sep 17 00:00:00 2001 From: Mitja Felicijan Date: Sat, 8 Jul 2023 23:25:41 +0200 Subject: Moved to a simpler SSG --- ...021-12-25-running-golang-application-as-pid1.md | 347 --------------------- 1 file changed, 347 deletions(-) delete mode 100644 content/posts/2021-12-25-running-golang-application-as-pid1.md (limited to 'content/posts/2021-12-25-running-golang-application-as-pid1.md') diff --git a/content/posts/2021-12-25-running-golang-application-as-pid1.md b/content/posts/2021-12-25-running-golang-application-as-pid1.md deleted file mode 100644 index 60d0400..0000000 --- a/content/posts/2021-12-25-running-golang-application-as-pid1.md +++ /dev/null @@ -1,347 +0,0 @@ ---- -title: Running Golang application as PID 1 with Linux kernel -url: running-golang-application-as-pid1.html -date: 2021-12-25T12:00:00+02:00 -draft: false ---- - -## Unikernels, kernels, and alike - -I have been reading a lot about -[unikernernels](https://en.wikipedia.org/wiki/Unikernel) lately and found them -very intriguing. When you push away all the marketing speak and look at the -idea, it makes a lot of sense. - -> A unikernel is a specialized, single address space machine image constructed -> by using library operating systems. ([Wikipedia](https://en.wikipedia.org/wiki/Unikernel)) - -I really like the explanation from the article -[Unikernels: Rise of the Virtual Library Operating System](https://queue.acm.org/detail.cfm?id=2566628). -Really worth a read. - -If we compare a normal operating system to a unikernel side by side, they would -look something like this. - -![Virtual machines vs Containers vs Unikernels](/assets/pid1/unikernels.png) - -From this image, we can see how the complexity significantly decreases with -the use of Unikernels. This comes with a price, of course. Unikernels are hard -to get running and require a lot of work since you don't have an actual proper -kernel running in the background providing network access and drivers etc. - -So as a half step to make the stack simpler, I started looking into using -Linux kernel as a base and going from there. I came across this -[Youtube video talking about Building the Simplest Possible Linux System](https://www.youtube.com/watch?v=Sk9TatW9ino) -by [Rob Landley](https://landley.net) and apart from statically compiling the -application to be run as PID1 there was really no other obstacles. - -## What is PID 1? - -PID 1 is the first process that Linux kernel starts after the boot process. -It also has a couple of unique properties that are unique to it. - -- When the process with PID 1 dies for any reason, all other processes are - killed with KILL signal. -- When any process having children dies for any reason, its children are - re-parented to process with PID 1. -- Many signals which have default action of Term do not have one for PID 1. -- When the process with PID 1 dies for any reason, kernel panics, which - result in system crash. - -PID 1 is considered as an Init application which takes care of running other -and handling services like: - -- sshd, -- nginx, -- pulseaudio, -- etc. - -If you are on a Linux machine, you can check what your process is with PID 1 -by running the following. - -```sh -$ cat /proc/1/status -Name: systemd -Umask: 0000 -State: S (sleeping) -Tgid: 1 -Ngid: 0 -Pid: 1 -PPid: 0 -... -``` - -As we can see on my machine the process with id of 1 is [systemd](https://systemd.io/) -which is a software suite that provides an array of system components for Linux -operating systems. If you look closely you can also see that the `PPid` -(process id of the parent process) is `0` which additionally confirms that -this process doesn't have a parent. - -## So why even run application as PID 1 instead of just using a container? - -Containers are wonderful, but they come with a lot of baggage. And because they -are in their nature layered, the images require quite a lot of space and also a -lot of additional software to handle them. They are not as lightweight as they -seem, and many popular images require 500 MB plus disk space. - -The idea of running this as PID 1 would result in a significantly smaller footprint, -as we will see later in the post. - -> You could run a simple init system inside Docker container described more -> in this article [Docker and the PID 1 zombie reaping problem](https://blog.phusion.nl/2015/01/20/docker-and-the-pid-1-zombie-reaping-problem/). - -## The master plan - -1. Compile Linux kernel with the default definitions. -2. Prepare a Hello World application in Golang that is statically compiled. -3. Run it with [QEMU](https://www.qemu.org/) and providing Golang application - as init application / PID 1. - -For the sake of simplicity we will not be cross-compiling any of it and just -use the 64bit version. - -## Compiling Linux kernel - -```sh -$ wget https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.15.7.tar.xz -$ tar xf linux-5.15.7.tar.xz - -$ cd linux-5.15.7 - -$ make clean - -# read more about this https://stackoverflow.com/a/41886394 -$ make defconfig - -$ time make -j `nproc` - -$ cd .. -``` - -At this point we have kernel image that is located in `arch/x86_64/boot/bzImage`. -We will use this in QEMU later. - -To make our lives a bit easier lets move the kernel image to another place. -Lets create a folder `bin/` in the root of our project with `mkdir -p bin`. - - -At this point we can copy `bzImage` to `bin/` folder with -`cp linux-5.15.7/arch/x86_64/boot/bzImage bin/bzImage`. - -The folder structure of this experiment should look like this. - -``` -pid1/ - bin/ - bzImage - linux-5.15.7/ - linux-5.15.7.tar.xz -``` - -## Preparing PID 1 application in Golang - -This step is relatively easy. The only thing we must have in mind that we will -need to compile the binary as a static one. - -Let's create `init.go` file in the root of the project. - -```go -package main - -import ( - "fmt" - "time" -) - -func main() { - for { - fmt.Println("Hello from Golang") - time.Sleep(1 * time.Second) - } -} -``` - -If you notice, we have a forever loop in the main, with a simple sleep of 1 -second to not overwhelm the CPU. This is because PID 1 should never complete -and/or exit. That would result in a kernel panic. Which is BAD! - -There are two ways of compiling Golang application. Statically and dynamically. - -To statically compile the binary, use the following command. - -```sh -$ go build -ldflags="-extldflags=-static" init.go -``` - -We can also check if the binary is statically compiled with: - -```sh -$ file init -init: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, Go BuildID=Ypu8Zw_4NBxm1Yxg2OYO/H5x721rQ9uTPiDVh-VqP/vZN7kXfGG1zhX_qdHMgH/9vBfmK81tFrygfOXDEOo, not stripped - -$ ldd init -not a dynamic executable -``` - -At this point, we need to create [initramfs](https://www.linuxfromscratch.org/blfs/view/svn/postlfs/initramfs.html) -(abbreviated from "initial RAM file system", is the successor of initrd. It -is a cpio archive of the initial file system that gets loaded into memory -during the Linux startup process). - -```sh -$ echo init | cpio -o --format=newc > initramfs -$ mv initramfs bin/initramfs -``` - -The projects at this stage should look like this. - -``` -pid1/ - bin/ - bzImage - initramfs - linux-5.15.7/ - linux-5.15.7.tar.xz - init.go -``` - -## Running all of it with QEMU - -[QEMU](https://www.qemu.org/) is a free and open-source hypervisor. It emulates -the machine's processor through dynamic binary translation and provides a set -of different hardware and device models for the machine, enabling it to run a -variety of guest operating systems. - -```sh -$ qemu-system-x86_64 -serial stdio -kernel bin/bzImage -initrd bin/initramfs -append "console=ttyS0" -m 128 -``` - -```sh -$ qemu-system-x86_64 -serial stdio -kernel bin/bzImage -initrd bin/initramfs -append "console=ttyS0" -m 128 -[ 0.000000] Linux version 5.15.7 (m@khan) (gcc (GCC) 11.2.1 20211203 (Red Hat 11.2.1-7), GNU ld version 2.37-10.fc35) #7 SMP Mon Dec 13 10:23:25 CET 2021 -[ 0.000000] Command line: console=ttyS0 -[ 0.000000] x86/fpu: x87 FPU will use FXSAVE -[ 0.000000] signal: max sigframe size: 1440 -[ 0.000000] BIOS-provided physical RAM map: -[ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable -[ 0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved -[ 0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved -[ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000007fdffff] usable -[ 0.000000] BIOS-e820: [mem 0x0000000007fe0000-0x0000000007ffffff] reserved -[ 0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved -[ 0.000000] NX (Execute Disable) protection: active -[ 0.000000] SMBIOS 2.8 present. -[ 0.000000] DMI: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-6.fc35 04/01/2014 -[ 0.000000] tsc: Fast TSC calibration failed -... -[ 2.016106] ALSA device list: -[ 2.016329] No soundcards found. -[ 2.053176] Freeing unused kernel image (initmem) memory: 1368K -[ 2.056095] Write protecting the kernel read-only data: 20480k -[ 2.058248] Freeing unused kernel image (text/rodata gap) memory: 2032K -[ 2.058811] Freeing unused kernel image (rodata/data gap) memory: 500K -[ 2.059164] Run /init as init process -Hello from Golang -[ 2.386879] tsc: Refined TSC clocksource calibration: 3192.032 MHz -[ 2.387114] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x2e02e31fa14, max_idle_ns: 440795264947 ns -[ 2.387380] clocksource: Switched to clocksource tsc -[ 2.587895] input: ImExPS/2 Generic Explorer Mouse as /devices/platform/i8042/serio1/input/input3 -Hello from Golang -Hello from Golang -Hello from Golang -``` - -The whole [log file here](/assets/pid1/qemu.log). - -## Size comparison - -The cool thing about this approach is that the Linux kernel and the application -together only take around 12 MB, which is impressive as hell. And we need to -also know that the size of bzImage (Linux kernel) could be greatly decreased -by going into `make menuconfig` and removing a ton of features from the kernel, -making the size even smaller. I managed to get kernel size down to 2 MB and -still working properly. - -```sh -total 12M --rw-r--r--. 1 m m 9.3M Dec 13 10:24 bzImage --rw-r--r--. 1 m m 1.9M Dec 27 01:19 initramfs -``` - -## Creating ISO image and running it with Gnome Boxes - -First we need to create proper folder structure with `mkdir -p iso/boot/grub`. - -Then we need to download the [grub binary](https://github.com/littleosbook/littleosbook/raw/master/files/stage2_eltorito). -You can read more about this program on https://github.com/littleosbook/littleosbook. - -```sh -$ wget -O iso/boot/grub/stage2_eltorito https://github.com/littleosbook/littleosbook/raw/master/files/stage2_eltorito -``` - -```sh -$ tree iso/boot/ -iso/boot/ -├── bzImage -├── grub -│   ├── menu.lst -│   └── stage2_eltorito -└── initramfs -``` - -Let's copy files into proper folders. - - -```sh -$ cp stage2_eltorito iso/boot/grub/ -$ cp bin/bzImage iso/boot/ -$ cp bin/initramfs iso/boot/ -``` - -Lets create a GRUB config file at `nano iso/boot/grub/menu.lst` with contents. - -```ini -default=0 -timeout=5 - -title GoAsPID1 -kernel /boot/bzImage -initrd /boot/initramfs -``` - -Let's create iso file by using genisoimage: - -```sh -genisoimage -R \ - -b boot/grub/stage2_eltorito \ - -no-emul-boot \ - -boot-load-size 4 \ - -A os \ - -input-charset utf8 \ - -quiet \ - -boot-info-table \ - -o GoAsPID1.iso \ - iso -``` - -This will produce `GoAsPID1.iso` which you can use with [Virtualbox](https://www.virtualbox.org/) -or [Gnome Boxes](https://apps.gnome.org/app/org.gnome.Boxes/). - - - -## Is running applications as PID 1 even worth it? - -Well, the answer to this is not as simple as one would think. Sometimes it is -and sometimes it's not. For embedded systems and very specialized applications -it is worth for sure. But in normal uses, I don't think so. It was an interesting -exercise in compiling kernels and looking at the guts of the Linux kernel, -but sticking to containers for most of the things is a better option in my -opinion. - -An interesting experiment would be creating an image that supports networking -and could be deployed to AWS as an EC2 instance and observing how it fares. -But in that case, we would need to write some sort of supervisor that would -run on a separate EC2 that would check if other EC2 instances are running -properly. Remember that if your application fails, kernel panics and the -whole machine is inoperable in this case. - -- cgit v1.2.3