Managing Multiple Machines Simultaneously With Ansible

If I have to do it more than once, it’s probably going to get scripted. That has been my general attitude towards mundane system administration tasks for many years, and is also shared by many others. How about taking that idea a little further and applying it to multiple machines? Well there’s a tool for that too, and it’s named ansible.

We need ansible installed on the system we will be using as the client/bastion. This machine needs to be able to SSH into all of the remote systems we want to manage without issue. So stop and make sure that works unhindered before continuing. On the remote machine, the requirements are fairly low and typically revolve around python2. In Gentoo python2 is already installed as it is required by several things including emerge itself. On Ubuntu 16.04 LTS, python2 is not installed by default and you will need to install the package ‘python-minimal’ to regain it.

Once we have python installed on the remote machines and ansible installed on the local machine, we can move on to editing the ansible configuration with a list of our hosts. This file is fairly simple and there are lots of examples available, but here is a snippet of my /etc/ansible/hosts file:

[ubuntu-staging]
ubuntu-staging-dev
ubuntu-staging-www
ubuntu-staging-db

 

Here you can see I have three hosts listed under a group named ubuntu-staging.

Once we have hosts defined we can do a simple command line test:

ansible ubuntu-staging -m command -a “w”

The ‘-m’ tells ansible we wish to use a module named ‘command’ and ‘-a’ indicates that it has arguments that need to be passed which is immediately given as ‘w’. The output from this command should be similar to this:

$ ansible ubuntu-staging -m command -a “w”
ubuntu-staging-www | SUCCESS | rc=0 >>
10:25:57 up 8 days, 12:29, 1 user, load average: 0.22, 0.31, 0.35
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
canuteth pts/2 192.168.13.221 10:25 1.00s 0.25s 0.01s w

ubuntu-staging-dev | SUCCESS | rc=0 >>
10:25:59 up 8 days, 12:17, 1 user, load average: 0.16, 0.03, 0.01
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
canuteth pts/0 192.168.13.221 10:25 0.00s 0.37s 0.00s w

ubuntu-staging-db | SUCCESS | rc=0 >>
10:26:02 up 8 days, 12:25, 1 user, load average: 0.17, 0.09, 0.09
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
canuteth pts/0 192.168.13.221 10:26 0.00s 0.28s 0.00s w

Okay, that shows promise right? Let’s try something a little more complicated:

$ ansible ubuntu-staging -s -K -m command -a “apt-get update”
SUDO password:
[WARNING]: Consider using apt module rather than running apt-get

ubuntu-staging-db | SUCCESS | rc=0 >>
Hit:1 http://us.archive.ubuntu.com/ubuntu xenial InRelease
Get:2 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease [102 kB]
Get:3 http://security.ubuntu.com/ubuntu xenial-security InRelease [102 kB]
Get:4 http://us.archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB]
Fetched 306 kB in 5s (59.3 kB/s)
Reading package lists…

ubuntu-staging-www | SUCCESS | rc=0 >>
Hit:1 http://us.archive.ubuntu.com/ubuntu xenial InRelease
Get:2 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease [102 kB]
Get:3 http://security.ubuntu.com/ubuntu xenial-security InRelease [102 kB]
Hit:4 https://apt.dockerproject.org/repo ubuntu-xenial InRelease
Get:5 http://us.archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages [544 kB]
Get:7 http://us.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages [528 kB]
Get:8 http://us.archive.ubuntu.com/ubuntu xenial-updates/main Translation-en [220 kB]
Get:9 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 Packages [471 kB]
Get:10 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe i386 Packages [456 kB]
Get:11 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe Translation-en [185 kB]
Get:12 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages [276 kB]
Get:13 http://security.ubuntu.com/ubuntu xenial-security/main i386 Packages [263 kB]
Get:14 http://security.ubuntu.com/ubuntu xenial-security/main Translation-en [118 kB]
Get:15 http://security.ubuntu.com/ubuntu xenial-security/universe amd64 Packages [124 kB]
Get:16 http://security.ubuntu.com/ubuntu xenial-security/universe i386 Packages [111 kB]
Get:17 http://security.ubuntu.com/ubuntu xenial-security/universe Translation-en [64.2 kB]
Fetched 3,666 kB in 6s (598 kB/s)
Reading package lists…

ubuntu-staging-dev | SUCCESS | rc=0 >>
Hit:1 http://us.archive.ubuntu.com/ubuntu zesty InRelease
Get:2 http://us.archive.ubuntu.com/ubuntu zesty-updates InRelease [89.2 kB]
Get:3 http://security.ubuntu.com/ubuntu zesty-security InRelease [89.2 kB]
Get:4 http://us.archive.ubuntu.com/ubuntu zesty-backports InRelease [89.2 kB]
Get:5 http://us.archive.ubuntu.com/ubuntu zesty-updates/main i386 Packages [94.4 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu zesty-updates/main amd64 Packages [96.2 kB]
Get:7 http://us.archive.ubuntu.com/ubuntu zesty-updates/main Translation-en [43.0 kB]
Get:8 http://us.archive.ubuntu.com/ubuntu zesty-updates/main amd64 DEP-11 Metadata [41.8 kB]
Get:9 http://us.archive.ubuntu.com/ubuntu zesty-updates/main DEP-11 64×64 Icons [14.0 kB]
Get:10 http://us.archive.ubuntu.com/ubuntu zesty-updates/universe i386 Packages [53.4 kB]
Get:11 http://us.archive.ubuntu.com/ubuntu zesty-updates/universe amd64 Packages [53.5 kB]
Get:12 http://us.archive.ubuntu.com/ubuntu zesty-updates/universe Translation-en [31.1 kB]
Get:13 http://us.archive.ubuntu.com/ubuntu zesty-updates/universe amd64 DEP-11 Metadata [54.1 kB]
Get:14 http://us.archive.ubuntu.com/ubuntu zesty-updates/universe DEP-11 64×64 Icons [43.5 kB]
Get:15 http://us.archive.ubuntu.com/ubuntu zesty-updates/multiverse amd64 DEP-11 Metadata [2,464 B]
Get:16 http://us.archive.ubuntu.com/ubuntu zesty-backports/universe amd64 DEP-11 Metadata [3,980 B]
Get:17 http://security.ubuntu.com/ubuntu zesty-security/main amd64 Packages [67.0 kB]
Get:18 http://security.ubuntu.com/ubuntu zesty-security/main i386 Packages [65.5 kB]
Get:19 http://security.ubuntu.com/ubuntu zesty-security/main Translation-en [29.6 kB]
Get:20 http://security.ubuntu.com/ubuntu zesty-security/main amd64 DEP-11 Metadata [5,812 B]
Get:21 http://security.ubuntu.com/ubuntu zesty-security/universe amd64 Packages [28.8 kB]
Get:22 http://security.ubuntu.com/ubuntu zesty-security/universe i386 Packages [28.7 kB]
Get:23 http://security.ubuntu.com/ubuntu zesty-security/universe Translation-en [19.9 kB]
Get:24 http://security.ubuntu.com/ubuntu zesty-security/universe amd64 DEP-11 Metadata [5,040 B]
Fetched 1,049 kB in 6s (168 kB/s)
Reading package lists…

This time we passed ansible the paramater ‘-s’ which tells ansible we want to use sudo and we also passed ‘-K’ which tells ansible to prompt us for a password. You’ll also notice that it warns us to use the ‘apt’ module, which is a better choice for interacting with apt-get.

The command module will work with pretty much any command that is non-interactive and doesn’t use pipes or redirection. I often use it for checking things on multiple machines quickly. For example, if I need to install updates and I want to know if anyone is using a particular machine, I can use w, who, users, etc. to see who is logged in before proceeding.

If we needed to interact with one a few hosts and not an entire group, we can name the hosts, separated by a comma, in the same fashion: ‘ansible ubuntu-staging-www,ubuntu-staging-db …’

Now lets look at trying something a bit more complicated.. say we need to copy a configuration file /etc/ssmtp/ssmtp.conf to all of our hosts. For this we will write an ansible playbook that I named ssmtp.yml:


# copy ssmtp.conf to all ubuntu-staging hosts

– hosts: ubuntu-staging
user: canutethegreat
sudo: yes

tasks:
– copy: src=/home/canutethegreat/staging/conf/etc/ssmtp/ssmtp.conf
dest=/etc/ssmtp/ssmtp.conf
owner=root
group=ssmtp
mode=0640

We can invoke the command with ‘ansible-playbook ssmtp.yml’ and it will do as directed. The syntax is fairly straightforward and there are quite a number of examples.

There are lots of examples for a wide range of tasks in the Ansible github repo and be sure to take a look at the intro to playbooks page. Just remember that you are doing things to multiple servers at once so if you do something dumb it’ll be carried out on all of the selected servers! Testing things on staging servers and using pretend/simulate are always good ideas anyway.

Advertisements