January 09, 2015

Today I learned: Bash and Ansible

Iterating through strings

Bash guides (like this) typically talk about arrays in terms of globs. Makes sense, since that’s a really common use.

But sometimes you want to be able to iterate through plain old strings, like this where we iterate through three words and for each of those iterate through two others so we can generate some commands:

if [ $DIRECTION == "delete" ]; then
  for node in API Web Worker; do
    for action in daily-spinup daily-spindown; do
      aws autoscaling delete-scheduled-action --auto-scaling-group-name ${AWS_ENV}${node} --scheduled-action-name $action
    done
  done
fi

which will wind up generating six commands, assuming AWS_ENV=qa:

aws autoscaling delete-scheduled-action --auto-scaling-group-name qaAPI --scheduled-action-name daily-spinup
aws autoscaling delete-scheduled-action --auto-scaling-group-name qaAPI --scheduled-action-name daily-spindown
aws autoscaling delete-scheduled-action --auto-scaling-group-name qaWeb --scheduled-action-name daily-spinup
aws autoscaling delete-scheduled-action --auto-scaling-group-name qaWeb --scheduled-action-name daily-spindown
aws autoscaling delete-scheduled-action --auto-scaling-group-name qaWorker --scheduled-action-name daily-spinup
aws autoscaling delete-scheduled-action --auto-scaling-group-name qaWorker --scheduled-action-name daily-spindown

This doc has a lot of good examples.

Refreshing Ansible’s EC2 cache

Bringing environments up and down every day means that Ansible’s EC2 cache can get invalid much quicker. You can invalidate it, and check the results, with:

$ ./ec2.py --refresh-cache
{
  "_meta": {
    "hostvars": {
   ... loads of JSON ...
    }
}

$ ls -al ~/.ansible/tmp/
ubuntu@ip-10-3-81-9:~$ ls -al ~/.ansible/tmp/
total 72
drwxrwxr-x 4 ubuntu ubuntu  4096 Jan  9 01:22 .
drwxrwxr-x 4 ubuntu ubuntu  4096 Jul  7  2014 ..
-rw-rw-r-- 1 ubuntu ubuntu 49794 Jan  9 14:54 ansible-ec2.cache
-rw-rw-r-- 1 ubuntu ubuntu  1170 Jan  9 14:54 ansible-ec2.index
...

as mentioned in the docs.

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