In Chef, why are raised exceptions not rescued? - ruby

Question

In Chef, Why does this code not catch the thrown exception in the bash resource? If I run this code, I never ever get to the python resource even when the exception is thrown. The error is expected, which is why I'm catching it, and then going over to pymongo and fixing it that way.
begin
bash "mongo fix" do
code "mongo --verbose #{filename}"
action :run
end
rescue
python 'pymongo reconfig' do
code "Pymongo does a catch and reconfig"
end
end
And this is the exception output
[2013-03-05T20:03:55+00:00] FATAL: Mixlib::ShellOut::ShellCommandFailed: bash[mongo fix (noudata::mongo line 77) had an error: Mixlib::ShellOut::ShellCommandFailed: Expected process to exit with [0], but received '253'
---- Begin output of "bash" "/tmp/chef-script20130305-3916-14xxhn5-0" ----
STDOUT: MongoDB shell version: 2.2.3
Tue Mar 5 20:03:55 versionCmpTest passed
Tue Mar 5 20:03:55 versionArrayTest passed
connecting to: test
Tue Mar 5 20:03:55 creating new connection to:127.0.0.1:27017
Tue Mar 5 20:03:55 BackgroundJob starting: ConnectBG
Tue Mar 5 20:03:55 connected connection!
true
{
"errmsg" : "replSetReconfig command must be sent to the current replica set primary.",
"ok" : 0
}
Tue Mar 5 20:03:55 uncaught exception: [object bson_object]
failed to load: /tmp/test.js
STDERR:
---- End output of "bash" "/tmp/chef-script20130305-3916-14xxhn5-0" ----
Ran "bash" "/tmp/chef-script20130305-3916-14xxhn5-0" returned 253

Answer 1

The code in the begin block makes an instance of a Chef::Resource::Bash resource, assigns the resource's code and action attributes, and adds the resource to run_context.resource_collection. The resource is not "run" in any sense. Making an instance of the resource does not raise any exceptions, so the code in the rescue block is not run.
Later on, once all of your recipe code has finished running, Chef will loop over the resources in the run_context.resource_collection. For each resource, Chef will run the resource's actions. In the case of a bash resource, that means running the string given in the resource's code attribute. Notice that this happens well after your recipe and all other recipes have finished running, and so this happens well outside of your begin block. Any exceptions raised by this resource when its actions are run do not propagate to your begin block, because the actions are not called from within your begin block, but from well after it.
You can try something like this:
bash "mongo fix" do
code "mongo --verbose #{filename} || python pymongo reconfig"
end

Answer 2

Put your code in definition and call definition from the recipe.