Cluster Management Made Easy with Ansible

Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

Installation¶

:::bash
sudo pip3 install ansible

Configuration¶

Ansible looks for configuration file in the following order.

ansible.cfg in the current directory.
~/.ansible.cfg
/etc/ansible.cfg

Examples¶

Copy a file to each machine in the cluster.

:::bash
proxychains ansible all \
    -i hosts \
    --user=stack \
    --private-key=~/.ssh/rsa \
    -m copy \
    -a "src=../pkg.tar.gz dest=~/"

Install an R package on each machine in the cluster.

:::bash
proxychains ansible all \
    -i hosts \
    --user=stack \
    --private-key=~/.ssh/spot_rsa \
    -a 'Rscript -e "install.packages(\"../pkg.tar.gz\")"'

Host Key Checking¶

Ansible 1.2.1 and later have host key checking enabled by default. If a machine in the cluster is reimaged, it will result in an error message (host fingerprint changed). This can be fixed by removing keys from ~/.ssh/known_hosts. If a machine in the cluster is not in ~/.ssh/known_hosts, it will prompt for confirmation of adding the host as a known one. To avoid those interuptions, you can add the following into your Ansible configuration file.

:::text
[defaults]
host_key_checking = False

Alternatively this can be set by an environment variable:

:::bash
export ANSIBLE_HOST_KEY_CHECKING=False

Also note that host key checking in paramiko mode is slow, therefore switching to ssh is recommended when you have host key checking enabled in Ansible.

References¶

http://www.legendu.net/misc/blog/run-commands-on-remote-machines/

https://github.com/ansible/ansible

https://serversforhackers.com/running-ansible-programmatically