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Once upon a time there was chroot (notice, it's just 50LOC?!). chroot was a simple way of sandboxing your application, namely just filesystem isolation. chroot lacked some features people wanted and alongs came Docker, which is a front end to LXC. It works, though it has a LOT of SLOC/complexity/features. Docker is monolithic and depends on Linux.

Today we have general packaged distributions like Debian & Archlinux. Their main fault was probably being too general, poor abilities to upgrade and downgrade. Along comes CoreOS, a lightweight Linux OS with (a modern, but hugely controversial init) systemd, heavyweight btrfs & docker. CoreOS is also monolithic and depends on Linux.

I've attempted to understand CoreOS before, though since I needed to move Greptweet to a VPS with more disk space... quickly... I "deep dived" into CoreOS & Docker and here is my writeup of the experience. Tip #1, the default user for CoreOS is "core", e.g. ssh core@ once you get for e.g. your CoreOS droplet going.


The 20LOC Greptweet Dockerfile took me almost all day to create, though this was my favourite accomplishment. I studied other Archlinux and Ubuntu docker files on Github to give me guidance how to achieve this.

So now I have a succinct file that describes Greptweet's environment to function. I found it astonishing the container for running a PHP app on Nginx is almost 1GB!

Yes, I need to re-implement greptweet in Golang to greatly reduce this huge bloat of a dependency!

Read only filesystem on CoreOS means no superuser or what?

I was hoping CoreOS would do away with root altogether. I'm seriously tired of sudo. I noticed read only mounts, whilst trying to disable password ssh logins to avoid loads of:

Failed password for root from $badman_IP port $highport ssh2

In my journalctl. Ok, if they are going to fix the config of sshd_config I thought, maybe they would do away with root?! PLEASE.

Update: If you discover WHERE sshd_config is managed in git by the CoreOS, I will give you a MAN HUG. CoreOS have totally obfuscated how they maintain configurations, compared to Archlinux packages!!

Haunting permissions

I hate UNIX permissions, hate hate hate. So with Docker your data is mounted on the host IIUC and your app stays firmly containerized.

But when your app writes data out on to a mount point, what THE HELL should the permissions be? I ended up just chmod -R 777 on my Volume's mountpoint, though I should probably have used setfacl What a mess!

User/group 33

How am I supposed to log CoreOS/Docker?!

I'm confused about Volume mounts. I run Greptweet like so: /usr/bin/docker run --name greptweet1 -v /srv/www/ -p 80:80 greptweet, and /srv/http/u/ is where the data lives. But HOW am I supposed to get at my container's logs? Another volume mount?

How does CoreOS envision managing httpd logs? I don't understand. And how am I supposed to run logrorate!? "One step forward, two steps back" is playing in my mind.


A jarring thing is that when you run a docker container, you IIUC are expected to run one process, i.e. the httpd.

Unfortunately with nginx, to get PHP working you need to run a separate (FastCGI) PHP process to nginx httpd, hence the Greptweet Dockerfile uses Python's supervisor daemon to manage both processes. Urgh. I copied this paradigm from another Dockerfile. Tbh I was expecting to manage the process with systemd inside the container. Now I have Python crapware in my container for managing nginx/php processes. Suck.

NO Cron

Greptweet used cron to create backups, relay stats and generate reports. Now AFAICT I don't have the basic utility of cron in my container. Now what?!


Update: We are suppose to use systemd timers


As mentioned in my previous blog on CoreOS, I was quite excited about have "free" updates to my core host system. Sadly after looking at the logs, I'm not impressed.

There is little visibility to the actual update. I have recently found but it uses some horrible XML manifest to layer on the updates. Why can't the whole rootfs just be in git ffs?

Furthermore I noticed locksmithd which I think reboots the machine, but I'm not sure.

Oct 18 03:11:11 dc update_engine[458]: <request protocol="3.0" version="CoreOSUpdateEngine-" updaterversion="CoreOSUpdateEngine-0
Oct 18 03:11:11 dc update_engine[458]: <os version="Chateau" platform="CoreOS" sp="444.5.0_x86_64"></os>
Oct 18 03:11:11 dc update_engine[458]: <app appid="{e96281a6-d1af-4bde-9a0a-97b76e56dc57}" version="444.5.0" track="stable" from_track="
Oct 18 03:11:11 dc update_engine[458]: <ping active="1"></ping>
Oct 18 03:11:11 dc update_engine[458]: <updatecheck targetversionprefix=""></updatecheck>
Oct 18 03:11:11 dc update_engine[458]: <event eventtype="3" eventresult="2" previousversion=""></event>
Oct 18 03:11:11 dc update_engine[458]: </app>
Oct 18 03:11:11 dc update_engine[458]: </request>

I've glanced over several times now and it's still not clear to me. As an operating system maintainer myself for Webconverger updates, our gitfs upgrade system is MUCH CLEARER than how CoreOS updates are handled. I wonder wth Docker 1.3 is going to hit CoreOS stable.

Keeping my Archlinux docker container uptodate is also a bit of a mystery to me...

CoreOS packaging is just WEIRD

It took me way too long to figure out how to enter a Docker 1.2 container and have a look. nsenter will be replaced by Docker 1.3's docker exec, but the way it installed was very intriguing.

In fact package management in CoreOS eyes I think means starting a share/privileged container and mapping it back to the host system. That's a pretty darn wild way of doing things imo.

I've been BATTLING TO GET TMUX running. It was suggested that this screen CoreOS install guide might help me. There is also an odd "toolbox" alias to a Fedora container with tools, but it doesn't map back to the host. All this for a terminal multiplexer. OMG.

Starting your Docker container in CoreOS was non-trivial

Here is Greptweet's service file.

CoreOS's launch guide was a bit strange to me. Am I supposed to publish my Greptweet image, so the docker pull works? It could be a lot simpler I feel. I.e. why doesn't the docker daemon manage/start the containers itself!?


I think the basic idea of lightweight host OS (CoreOS) and containers (Docker) has legs. I just wish it was as simple as chroot. Now I'm left thinking how Ansible/Chef/Puppet/Vagrant did such a bad job compared to the Dockerfile. Or perhaps blaming VPS hosters who never really got a decent API together to move/expand/inspect their VPS volumes.

Gosh, how did we get into this mess?!

So now system administrators now run hypervisors aka CoreOS and spin up VPSes aka Docker containers all by themselves. Seems like another level of abstraction that empowers system administrators but at the same time there is going to a raft of bugs/pain to enjoy with this "movement". It's also slightly concerning that CoreOS/Docker seems to fly in the face of the Unix philosophy.

My rating for CoreOS: 1 out of 5 stars


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