container to help manage a cluster of coreOS machines that boot via PXE

My first container, learning and work in progress!

Forked from the nice work at jpetazzo/pxe.

Notes:

• developed using IBM blades, with a serial console on ttyS1, and a private VLAN on ethernet 2, that is used for DHCP/PXE and coreOS comms only.
• "public" IP address of hosts (eth0) is set by cloud-config (provided by this container, customised for each host).
• DHCP subnet is currently hardcoded as a /24, from .10 to .250; but it should/could be even smaller, as we use reservations?...
• Yes, it sounds silly to read the config files on each request on the httpserver that serves cloud-configs, but this way you can change the config files on the data folder and not have to reload the container... Also, this reloading this should only happen when a host boots.

Enhancements over the original project:

• IP address and subnet for DHCP server and range are extracted from the IP address set on eth1 via pipework.
• boot different OSs based on configuration options.
• includes "smart" webserver to provide a personalised cloud-config to each host.

TODO:

• currently glued to the host that contains the data folder. find better, more independent storage option.
• don't run more than one of these on the same data folder...
• automatic process to update the coreos pxe files?
• web server should be able to provide static files also.

HOW DOES IT WORK:

When the container starts, it processes the pxe_hosts.json file, to create a dhcp_reservations and dhcp_options files for dnsmasq. pxelinux is configured to offer two config files, stable or beta, based on the channel you choose for your host.

It will also get the latest coreos release (stable and beta) and a pxelinux.0, if any of these files is not present on the data folder.

When the host boots, it will request a cloud-config file from this same container, provided by a python web server script running on port 8080. That script gets the client private IP address of the request, and replaces the variables on the default.yaml file, or from a custom yaml template, (represented by a $<variable>) for that host.

So you just have customise your default.yaml (or create multiple .yaml files if needed) for your hardware, and add hosts to your pxe_hosts.json.

As the original project, you need to setup on the host a bridge that has access to the pxe network, and then connect it to the container via pipework. If you see the default.yaml.sample file, the networking stuff there already sets a coreOS host with bridges in front of both ethernet interfaces of these IBM blades.

TO BUILD:

two options: git clone this repo:

$ git clone https://github.com/avlis/pxe_coreos pxe_coreos
$ cd pxe_coreos

or just download the Dockerfile.net into an empty folder (and rename it to Dockerfile):

$ mkdir pxe_coreos && cd pxe_coreos
$ wget https://github.com/avlis/pxe_coreos/Dockerfile.net -O Dockerfile

then:

$ docker build -t pxe_coreos .

TO LAUNCH:

make sure you have a proper default.yaml and a pxe_hosts.json file on your data folder! (in this example, it's in /home/core/pxe_coreos.data). Two samples are provided in this repo.

you can use a script similar to the one below (or the manage_pxe_container one) to start the container:

VLAN_ADDR=192.168.90.2
PXECID=$(docker run --cap-add NET_ADMIN -v /home/core/pxe_coreos.data:/cloudconfigserver/data -d pxe_coreos)
if [ -z "$PXECID" ]; then
   echo something bad happened, container not launched.
   exit 1
fi
sudo /home/core/pxe_coreos/bin/pipework br-internal $PXECID $VLAN_ADDR/24

MANAGEMENT & TROUBLESHOOTING:

check out the manage_pxe_container shell script on the utilites folder (on git, not on the container).

• make sure you have properly indented .yaml files, and a properly written (validate to be sure) pxe_hosts.json copied to the data dir.
• if running on a vm (e.g. virtualbox) make sure the bridged interface is in promiscuous mode so non bound ips are recieveing tftp requests.
• a while after the container starts, you should have 5 files on /tftp: pxelinux.0 and 4 coreosfiles: coreos_[beta|stable]_pxe[.vmlinuz|_image.cpio.gz]
• you can manually update those files and reboot your host, no need to restart the pxe_coreos container.
• check the output of the startup script with the docker logs command.
• check the content of /dnsmasq/dhcp_leases, to see if dnsmasq is giving IPs to hosts; get those mac addresses from that file and copy to new host entries on pxe_hosts.json
• you can check the cloud-config file from somewhere else, just add an ?override_ipv4=<ip> to the url: http://<ip of the container>:8080/?override_ipv4=<ip you want to check>
• for pxe stuff... tcpdump & wireshark are your friends...
• the httpserver reloads the config files at each request, but dnsmasq doesn't: you have to restart the container, or enter the container and execute the /cloudconfigserver/bin/reconfig.sh script.

docker exec -it $PXECID /bin/sh /cloudconfigserver/bin/reconfig.sh

PROTIP

Get a coreos container up and ready for running pxe_coreos using this cloud config.

#cloud-config

coreos:
  units:
    - name: br-internal.netdev
      runtime: true
      content: |
        [NetDev]
        Name=br-internal
        Kind=bridge
    - name: eth0.network
      runtime: true
      content: |
        [Match]
        Name=eth0

        [Network]
        Bridge=br-internal
    - name: br-internal.network
      runtime: true
      content: |
        [Match]
        Name=br-internal

        [Network]
        DNS=1.2.3.4
        Address=10.0.2.2/24