[chef] Re: Docker_container dependency hell


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  • From: Tensibai < >
  • To:
  • Subject: [chef] Re: Docker_container dependency hell
  • Date: Mon, 07 Sep 2015 10:18:20 +0200

 

Remarks inline

 

Here is what I am currently doing (simplified for readability)

docker_image image1 do

   action :nothing

   # built only based on notifications

end

docker_container container2 do

  action :run_if_missing

  subscribe :redeploy, "docker_image[image2]"

end

And in another cookbook:

docker_image image2 do

  action :nothing

  # built only based on notifications

end

docker_container container1 do

  action :run_if_missing

  subscribe :redeploy, "docker_image[image1]

  subscribe :redeploy, "docker_container[container2]

end

 

Problems with this approach:

- The containers are often built twice, first by the run_if_missing action, and then again by the redeploy action

- The run_if_missing action does not observe dependencies, so container1's run_if_missing action is actually invoked before container2 even exists, causing a build failure.

Don't you have a problem in your recipes order ? Out of notifications, you should ensure the run_list is coherent with the timeline of your provisionning, if the container2 was before container1 in the resource appearance order, it will be built before.

Another option could be to set a flag 'already_run' to define the subscribe attributes' only after first run, something along:

docker_container container1 do

  action :run_if_missing

  subscribe :redeploy, "docker_image[image1] if node.tagged?('flag')

  subscribe :redeploy, "docker_container[container2] if node.tagged?('flag')

end

 

# At end of recipe (could be improved to handle failure by doing it in a ruby_block and using notifications.)

node.tag('flag') # Flag could be generic or something named by container for a more precise approch

 

 

Obviously, I could circumvent this by changing the default action to :nothing, but then the containers aren't built at all if they are missing.

Also, using :immediate for the subscriptions is not an option (because then the redeploy action may get invoked too early and multiple times, and various other problems).

What is the best way to resolve this?

 

 

 



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