Core OS Characteristics and Technologies

• FastPatch update a second partition of the dual partition boot system for consisten upgrade and stable roll back.
• kexec (kernel exec) can be used for fastbooting. Essentially, kernel from the standby partition is loaded into memory, and it starts executing right away. This bypass BIOS hardware initialization and bootloader.
• /usr is mounted as read-only, since update is done as a whole new OS is installed on the passive partition.
• etcd, fleetd written in the GO programming language.
• Intra-node communication use std unix socket.
• inter-node communication uses SSH tunnel and auth (fleetctl).
• Originally used Docker exclusively, now have support for Rocket (rkt).
• fleet and locksmith may make CoreOS into a very interesting HPC system...

Initial install

CoreOS is build using ChromeOS' SDK.  
The doc all points to running CoreOS as a VM in the cloud, but 
it can actually run on bare metal.
The install ISO is 211 MB.  https://coreos.com/os/docs/latest/booting-with-iso.html

It provides only essentials so that it can run conainers (eg docker), 
utilizing cgroup and namespace for resource management and security.  
There are minimal additional functionality for service discovery and configuration sharing (via etcd).

Disk partition uses the newer GUID method.  
fdisk doesn't fully work.  coreos don't ship with gparted.  use cgpt instead.

partiton 3 (and 4 are the active/standby for USR-A and USR-B, respectively.  
GTP is flagged to boot from either one of this, and such boot partition will be set as read-only.
/usr in AWS CoreOS image used about 500 MB.
There are 482 uniq commands in /usr/bin, 260 in /usr/sbin 
(my cygwin has about 800 and 16 command in /bin and /sbin)

parttion 9 is for stateful / partition (only one of this, no standby.  upgrade don't change anything here?)
/ used about 666 MB

sudo cgpt show /dev/xvda	# show partition table, /usr will be booted on part with priority=1

etcd

1. etcd provides a replicated key-value store of all system configuration
2. each node in the cluster run a copy of etcd, thus HA and all data avail to all nodes.
3. Utilizes Raft algorithm for master election and consensus.
4. etcd also double as service discovery. Application announce themselves to etcd.
5. communication with etcd is thru REST (JSON on top of HTTP) http://127.0.0.1:4001/v2/keys/. These is accessible inside the container as well.
6. etcdctl is the cli interface. can read and set key-value pair

fleetd

1. cluster manager to control the systemd of each coreos node. ie, a distributed Init system
2. fleetclt provides a single point to manage process across the cluster, which is especially useful for managing HA apps.

locksmithd

Update/Reboot

Pros and Cons of CoreOS vs traditional Linux

Commands/Troubleshooting

sudo update_engine_client -update		# manually run upgrade, for debug/troubleshooting (update are automatic normally)

Reference

• wikipedia: CoreOS
• CoreOS components tutorial
• Using CoreOS
• CoreOS doc
• tba

Copyright info about this work

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike2.5 License. Pocket Sys Admin Survival Guide: for content that I wrote, (CC) some rights reserved. 2005,2012 Tin Ho [ tin6150 (at) gmail.com ]
Some contents are "cached" here for easy reference. Sources include man pages, vendor documents, online references, discussion groups, etc. Copyright of those are obviously those of the vendor and original authors. I am merely caching them here for quick reference and avoid broken URL problems.

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