These fit really nicely together if you want stick a web interface on system management tasks, such as deploying some code.
There’s a couple of gotchas with the way Celery uses fork to run a task though, as it removes the environment that the Celery task is running in.
If you do this:
@task def update(): run('ls')
It’ll fail with the above error. The fix is to do what the error says:
from Crypto import Random @task def update(): Random.atfork() run('ls')
This will initialise the Random Number Generator sufficiently for the paramiko ssh library that fabric is based on to connect.
You’re using fabric as an api, rather than using the fabric runner. This means the usual technique of doing:
from fabric.api import * env.hosts = ['192.168.0.1']
Won’t work, as there is no processing done on the env. The fix looks like this:
from fabric.api import * @task def update(): Random.atfork() env.host_string = 'ubuntu@192.168.0.1' run('ls')
If you need to connect to multiple hosts, you’ll have to do your own flow control.
This is more of a tip, and not a brilliant one at that. If you’re doing a lot of work with pregenerated VMs (such as the cloud providers), then destroying a VM on an IP, then rebuilding it, will cause the host key to change. Fabric uses your local .ssh/known_hosts for it’s connections, so this will probably cause the connection to fail as the keys will not match your previous one.
from fabric.api import * @task def update(): Random.atfork() env.host_string = 'ubuntu@192.168.0.1' env.disable_known_hosts = True run('ls')
disable_known_hosts will disable this behaviour, at the cost of some security, as you are no longer verifying that you are connecting to exactly the same machine. The current alternative seems to be that every time you rebuild a VM, you must remove it’s line from your known_hosts.
Each and every Celery task you use with Fabric, must set these variables, or it’ll fail. I’d recommend either inheriting your tasks, or creating a helper method to pop them all in, and call that at the start of your task.
Hope this helps someone.
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Sunday was biking at Cannock Chase. 10.5 k, in 1:11. Not too shabby, and good fun. Much more technical trail than Sherwood Pines.
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Of special note, the twine fabricated from a carrier bag and pure win.
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While awaiting Charlie to arrive on Friday due to traffic, I decided to
make Cake.
After some running around by my father to bring me a cake tin.
I made this: http://forkd.com/recipe/simple-fruit-cake-1369
Attached is a photo of a slice of said cake before people at work ate
it.
A day spent messing about in boats. In the sun. And real coffee to finish.
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