async actions in ansible playbooks
A number of people have been surprised by this feature, even though it is documented, so I thought I’d mention it.
Ansible can run actions async. This means it connects to the client system, starts the process and disconnects.
In general you would want all your plays to be synchronous (do thing X, wait for it to be done/watch it, do thing Y).
However, there are times when what you want to do will take a VERY long time or could kill your ssh connection off.
An example is a yum update:
tasks:
- name: yum update
action: command yum -y update
That can take a long time, depending on what’s going on. You want to monitor what it does, but you don’t want a timeout or a reset ssh session/network to kill off that process.
So what do you do? You make it async:
tasks:
- name: yum update
action: command yum -y update
async: 7200
poll: 15
That means – run yum -y update – wait for up to 7200s and poll every 15s to check on the status of the action.
Here’s where we’re using it in fedora:
http://infrastructure.fedoraproject.org/cgit/ansible.git/tree/playbooks/package-update.yml#n11
However, this means if your ssh or network were to die – the yum update process would still run to completion.
But if your connection does die and you cannot check on the status of the job what do you do?
Well -you can connect to any system as the user who was running the job and look in ~/.ansible_async
there will be a file in there for each job that was being run. It may just be a place holder and empty (if the job is still running) or it made be filled with the results if the job is finished.
Pretty handy for a variety of tasks.
