Demonstration of Ansible Features With Control & Test VMs
Posted by Jakub Holý on February 16, 2014
I have created a small project to demonstrate some features of Ansible, the new DevOps hotness, including Vagrant VMs for running Ansible and for testing the configuration. Either go straight to
or continue reading the copy & paste here.
This project has three things of interest:
- A non-trivial Ansible configuration that demonstrates couple of useful features and tricks
- A Vagrant/VirtualBox virtual machine with Ansible & co. to make it easy to run it (even on Windows)
- Another VM that can be used to test the configuration
And of course all the plumbing that makes them work together. It might be therefore a good base for Ansible projects of your own.
Disclaimer: I am quite new to Ansible.
Ansible is a devops tool for configuring servers over SSH, using just Python. It is similar to Puppet and Chef but does not need you to install anything on the servers (essentialy every *nix has Python 2.4+ and SSH, and it even works with the old RHEL 5.9), the configuration is by defaut pushed from the control machine instead of pulled by the servers, and it has strong focus on simplicity. It is less mature than Puppet and has fewer plugins and no support for Windows yet but the simplicity, minimal requirements, and push model are good reasons to consider it.
Vagrant is a command-line tool for creating, configuring, and managing virtual machines, f.ex. using VirtualBox. It also integrates them with the host machine by directory sharing, port forwarding, and password-less ssh. In essence, you need few text files and get a fully functional, configured, and integrated environment in a VM.
config.ssh.forward_agent = true in the
ansible-vm to make it easier to make your prive keys available to Ansible for SSH into remote machines. (See “Testing locally” below for more details.)
mount_options: ['dmode=0775','fmode=0664'] for mounting the directory with Ansible configuration so that the inventory file won’t seem to be executable to Ansible.
General: Use roles to split configuration into separate concerns (jboss, vagrant), use variables to handle variation between environments and usages of a role (f.ex. JBoss’ ports,
vagrant|staging|production). Use tags to mark parts of the configuration so that those parts can be picked and executed without the rest (f.ex.
Secret local credentials vars file: the configuration includes variables from the file
secret_vars.yml, which is added to
.gitignore so that it won’t be checked into Git and every user has to create her own local copy based on
secret_vars.yml.example. Thus sensitive credentials never leave the local machine.
Reuse via parametrized include and simulating
get_url. To avoid the need to keep downloaded archives, I use
stat to check for the presence of a file/directory and
while to skip
get_url if it exists. The whole thing is in a task include file,
roles/jboss/tasks/fetch-module.yml, that is parametrized so that it can be reused to fetch and unpack three different modules – see
Multiple environments – here
staging via two different inventory files.
If Ansible seems to freeze while executing a command, make sure that the command is not trying to ask for user input, as was my case with
unzip that wanted to know what to do with existing files (fixed by running it with
-o to force overwrite them).
JBoss configuration using Ansible so it is possible to automatically apply it to a server. Some of the files (-> templates) are parametrized with variables that are defined f.ex. in
group_vars/appservers, the host inventory file (f.ex.
secret_vars.yml and set the right credentials there.
You will need
- (Windows: ssh, f.ex. the one from the Putty installer)
- VirtualBox (f.ex. 4.3.6)
- Vagrant (f.ex. 1.4.3)
- Vagrant vbguest plugin (after having installed vagrant, run
vagrant plugin install vagrant-vbguest)
The Vagrant/VirtualBox VM
ansible-vm has Ansible installed and may be used to run it against the test VM or staging. The test VM itself,
centos-vm, may be used to test the changes locally before staging. As described above, you will need to create
secret_vars.yml with secret credentials.
Under Linux/Mac, you may install and use Ansible directly, without
Vagrant is a command-line tool that can create, set up, and manage VirtualBox virtual machines.
You need to know:
ansible-vmto create, configure, and start the VM
vagrant reloadafter you did
upfor the first time, if new Guest Additions were installed
vagrant sshto ssh into the machine as the user
vagrant, which has full sudo rights.
vagrant haltto stop a VM and
vagrant destroyif you want to destroy it (to re-create it from scratch)
Notice that Vagrant automatically shares the vm directory as
/vagrant with the VM (and we also share this directory as
/Infrastructure) and it can forward ports from the guest VM to the host so that you can access services running in the VM via
locahost:<the forwarded port> which we use a lot in the
Most of the config is inside “roles” such as “jboss” and “vagrant”, see the
Use the test CentOS VM. To enable password-less execution of ansible against the test VM, it is recommended to use ssh-agent, adding the vagrant key to it via
Windows: Use Git Bash and enable ssh-agent as described in GitHub Help, adding the line
ssh-add ~/.vagrant.d/insecure_private_key to it. Use the same Bash (?) to run
vagrant up under
Alternatively, run ansible with
-k, the password is “vagrant”.
- Run the test
centos-vm– go to the directory and run
ansible-vm– go to the directory and run
vagrant upand then
- In the Ansible VM run
cd /Infrastructureand run f.ex.
ansible-playbook -vi vagrant site.yml
ansible-vm setup assumes that IP of the host machine as visible from the VM is
10.0.2.2 (test with f.ex.
Ansible can try to predict some of the changes it would need to do:
ansible-playbook -vi staging site.yml -u <your user name> [--ask-sudo-pass] --check --diff
Infrastructure/ directory, run:
ansible-playbook -vi staging site.yml -u <your user name> [--ask-pass] [--ask-sudo-pass] [--tags <comma-separated tags>] [--private-key=key file]
- Ansible will ssh as the provided user to the machines listed in the staging file (“-u jakub” => “ssh jakub@app(1|2).staging.example.com”)
--ask-passis necessary if ssh asks for password, i.e. if you haven’t set up password-less ssh
-K) is necessary if your user hasn’t password-less sudo access on the server
- You can use
--tagsto execute only a subset of the tasks (provided the have been tagged); ex.:
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