dev-lxc

A tool for creating Chef server clusters using LXC containers.

Using ruby-lxc it builds a standalone server or tier cluster composed of a backend and multiple frontends with round-robin DNS resolution.

The dev-lxc tool is well suited as a tool for support related work, customized cluster builds for demo purposes, as well as general experimentation and exploration.

Features

  1. LXC 1.0 Containers - Resource efficient servers with fast start/stop times and standard init
  2. Btrfs - Storage efficient container backend provides fast container cloning
  3. Dnsmasq - DHCP networking and DNS resolution
  4. Base platforms - Containers that are built to resemble a traditional server
  5. ruby-lxc - Ruby bindings for LXC
  6. YAML - Simple, customizable definition of clusters; No more setting ENV variables
  7. Build process closely models the docs instructions

Its containers, standard init, networking and build process are designed to be similar to what you would build if you follow the product installation documentation so the end result is a cluster that is relatively similar to a more traditionally built cluster.

The Btrfs backed clones provides a quick clean slate which is so helpful especially for experimenting and troubleshooting. Or it can be used to build a customized cluster for demo purposes and be able to bring it up quickly and reliably.

While most of the plumbing is already in place for an HA cluster it actually can't be used since I haven't been able to get DRBD working inside containers yet.

If you aren't familiar with using containers please read this introduction.

LXC 1.0 Introduction

Requirements

The dev-lxc tool is designed to be used in platform built by the dev-lxc-platform cookbook.

Please follow the dev-lxc-platform usage instructions to create a suitable platform.

The cookbook will automatically install this dev-lxc tool.

Mounts and Packages (batteries not included)

As described below dev-lxc uses a YAML config file for each cluster.

This config file describes what directories get mounted from the Vagrant VM host into each container. You need to make sure that you configure the mount entries to be appropriate for your environment.

The same goes for the paths to each package. The paths that are provided in the default configs are just examples. You need to make sure that you have each package you want to use downloaded to appropriate directories that will be available to the container when it is started.

I recommend downloading the packages to a directory on your workstation. Then configure the dev-lxc-platform Vagrantfile to mount that directory in the Vagrant VM. Finally, configure the cluster's YAML config mount entries to mount the Vagrant VM directory into each container.

Upgrade dev-lxc gem

To upgrade the dev-lxc gem at any time you can run gem uninstall -x dev-lxc inside the Vagrant VM and then reprovision the VM using vagrant provision.

Usage

Shorter Commands are Faster (to type that is :)

I like to create an alias for dev-lxc for ease of use but for the purpose of these instructions I will use dev-lxc.

echo 'alias dl=dev-lxc' >> ~/.bashrc && source ~/.bashrc

You only have to type enough of a dev-lxc subcommand to make it unique.

The following commands are equivalent:

dev-lxc cluster init tier
dl cl i

dev-lxc cluster start
dl cl start

dev-lxc cluster destroy
dl cl d

Base Servers

One of the key things this tool uses is the concept of "base" servers. It creates servers with "b-" prepended to the name to signify it as a base server. Base servers are then snapshot cloned using the btrfs filesystem to provide very quick, lightweight duplicates of the base server that are either used to build another base server or a usable server.

The initial creation of base servers for the various platforms can take awhile so let's go ahead and start creating an Ubuntu 12.04 base server now.

dev-lxc create b-ubuntu-1204

You can see a menu of base servers this tool can create by using the following command.

dev-lxc create

Cluster Config Files

dev-lxc uses a yaml configuration file to define a cluster.

The following command generates sample config files for various cluster topologies.

dev-lxc cluster init

dev-lxc cluster init tier generates the following file:

base_platform: b-ubuntu-1204
topology: tier
api_fqdn: chef-tier.lxc
mounts:
  - /dev-shared dev-shared
packages:
  server: /dev-shared/chef-packages/ec/private-chef_11.1.2-1.ubuntu.12.04_amd64.deb
#  reporting: /dev-shared/chef-packages/ec/reporting/opscode-reporting_1.1.0-1.ubuntu.12.04_amd64.deb
#  push-jobs-server: /dev-shared/chef-packages/ec/push-jobs-server/opscode-push-jobs-server_1.1.0-1.ubuntu.12.04_amd64.deb
#  manage: /dev-shared/chef-packages/ec/manage/opscode-manage_1.1.1-1.ubuntu.12.04_amd64.deb
servers:
  be-tier.lxc:
    role: backend
    ipaddress: 10.0.3.202
    bootstrap: true
  fe1-tier.lxc:
    role: frontend
    ipaddress: 10.0.3.203
#  fe2-tier.lxc:
#    role: frontend
#    ipaddress: 10.0.3.204

This config defines a tier cluster consisting of a single backend and a single frontend. A second frontend is commented out to conserve resources.

If you uncomment the second frontend then both frontends will be created and dnsmasq will resolve the api_fqdn chef-tier.lxc to both frontends using a round-robin policy.

The config file is very customizable. You can add or remove mounts, packages or servers, change ip addresses, change server names, change the base_platform and more.

Make sure the mounts and packages represent paths that are available in your environment.

Managing Multiple Clusters

By default, dev-lxc looks for a dev-lxc.yaml file in the present working directory. You can also specify a particular config file as an option for most dev-lxc commands.

I use the following to avoid specifying each cluster's config file while managing multiple clusters.

mkdir -p ~/clusters/{clusterA,clusterB}
dev-lxc cluster init tier > ~/clusters/clusterA/dev-lxc.yaml
dev-lxc cluster init standalone > ~/clusters/clusterB/dev-lxc.yaml
cd ~/clusters/clusterA && dev-lxc cluster start  # starts clusterA
cd ~/clusters/clusterB && dev-lxc cluster start  # starts clusterB

Maintain Uniqueness Across Multiple Clusters

The default cluster configs are already designed to be unique from each other but as you build more clusters you have to maintain uniqueness across the YAML config files for the following items.

  1. Server names and api_fqdn

    Server names should really be unique across all clusters.

    Even when cluster A is shutdown, if cluster B uses the same server names when it is created it will use the already existing servers from cluster A.

    api_fqdn uniqueness only matters when clusters with the same api_fqdn are running.

    If cluster B is started with the same api_fqdn as an already running cluster A, then cluster B will overwrite cluster A's DNS resolution of api_fqdn.

    It is easy to provide uniqueness. For example, you can use the following command to replace -tier with -1234 in a tier cluster's config.

    sed -i 's/-tier/-1234/' dev-lxc.yaml

  2. IP Addresses

    IP addresses uniqueness only matters when clusters with the same IP's are running.

    If cluster B is started with the same IP's as an already running cluster A, then cluster B will overwrite cluster A's DHCP reservation of the IP's but dnsmasq will still refuse to assign the IP's to cluster B because they already in use by cluster A. dnsmasq then assigns random IP's from the DHCP pool to cluster B leaving it in an unexpected state.

    The dev-lxc-platform creates the IP range 10.0.3.150 - 254 for DHCP reserved IP's.

    Use unique IP's from that range when configuring clusters.

Create and Manage a Cluster

The following instructions will use a tier cluster for demonstration purposes. The size of this cluster uses about 3GB ram and takes a long time for the first build of the servers. Feel free to try the standalone config first.

The following command saves a predefined config to dev-lxc.yaml.

dev-lxc cluster init tier > dev-lxc.yaml

Starting the cluster the first time takes awhile since it has a lot to build.

The tool automatically creates snapshot clones at appropriate times so future creation of the cluster's servers is very quick.

dev-lxc cluster start

https://chef-tier.lxc resolves to the frontend.

Ponyville and wonderbolts orgs, users, knife.rb and keys are automatically created in the bootstrap backend server in /srv/piab/users for testing purposes.

Show the status of the cluster.

dev-cluster status

Stop the cluster's servers.

dev-lxc cluster stop

Clones of the servers as they existed immediately after initial installation and configuration are available so you can destroy the cluster and "rebuild" it within seconds effectively starting with a clean slate.

dev-lxc cluster destroy
dev-lxc cluster start

The abspath subcommand can be used to prepend each server's rootfs path to a particular file.

For example, to edit each server's private-chef.rb file you can use the following command.

emacs $(dev-lxc cluster abspath /etc/opscode/private-chef.rb)

After modifying the private-chef.rb you could use the run_command subcommand to tell each server to run private-chef-ctl reconfigure.

dev-lxc cluster run_command 'private-chef-ctl reconfigure'

Use the following command to destroy the cluster's servers and also destroy their corresponding base servers so you can build them from scratch.

dev-lxc cluster destroy -b

You can also run most of these commands against individual servers by using the server subcommand.

dev-lxc server ...

Using the dev-lxc library

dev-lxc can also be used as a library if preferred.

irb(main):001:0> require 'yaml'
irb(main):002:0> require 'dev-lxc'
irb(main):003:0> cluster = DevLXC::ChefCluster.new(YAML.load(IO.read('dev-lxc.yaml')))
irb(main):004:0> cluster.start
irb(main):005:0> server = DevLXC::ChefServer.new("fe1-tier.lxc", YAML.load(IO.read('dev-lxc.yaml')))
irb(main):006:0> server.stop
irb(main):007:0> server.start
irb(main):008:0> server.run_command("private-chef-ctl reconfigure")
irb(main):009:0> cluster.destroy

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request