Chef Deployment with irrelevant default symlinks - deployment

Question

I am trying to deploy my application code with Chef, which is working for one node and failing on another. I cannot determine why it works for one node and not another when they have the exact same config, but I can at least try to debug the problem on the node that fails.
deploy_revision app_config['deploy_dir'] do
scm_provider Chef::Provider::Git
repo app_config['deploy_repo']
revision app_config['deploy_branch']
if secrets["deploy_key"]
git_ssh_wrapper "#{app_config['deploy_dir']}/git-ssh-wrapper" # For private Git repos
end
enable_submodules true
shallow_clone false
symlink_before_migrate({}) # Symlinks to add before running db migrations
purge_before_symlink [] # Directories to delete before adding symlinks
create_dirs_before_symlink [] # Directories to create before adding symlinks
# symlinks()
action :deploy
restart_command do
service "apache2" do action :restart; end
end
end
This is my recipe for deploying the code. Notice that I have tried disabling symlinking entirely, as Chef always jams its own defaults in. Even with this I get the error:
================================================================================
Error executing action `deploy` on resource 'deploy_revision[/var/www]'
================================================================================
Chef::Exceptions::FileNotFound
------------------------------
Cannot symlink /var/www/shared/config/database.yml to /var/www/releases/7404041cf8859a35de90ae72091bea1628391075/config/database.yml before migrate: No such file or directory - /var/www/shared/config/database.yml or /var/www/releases/7404041cf8859a35de90ae72091bea1628391075/config/database.yml
Resource Declaration:
---------------------
# In /var/chef/cache/cookbooks/kapture/recipes/api.rb
68:
69: deploy_revision app_config['deploy_dir'] do
70: scm_provider Chef::Provider::Git
71: repo app_config['deploy_repo']
72: revision app_config['deploy_branch']
73: if secrets["deploy_key"]
74: git_ssh_wrapper "#{app_config['deploy_dir']}/git-ssh-wrapper" # For private Git repos
75: end
76: enable_submodules true
Compiled Resource:
------------------
# Declared in /var/chef/cache/cookbooks/kapture/recipes/api.rb:69:in `from_file'
deploy_revision("/var/www") do
destination "/var/www/shared/cached-copy"
symlink_before_migrate {"config/database.yml"=>"config/database.yml"}
updated_by_last_action true
restart_command #<Proc:0x00007f40f366e5a0#/var/chef/cache/cookbooks/kapture/recipes/api.rb:82>
repository_cache "cached-copy"
retries 0
keep_releases 5
create_dirs_before_symlink ["tmp", "public", "config"]
updated true
provider Chef::Provider::Deploy::Revision
enable_submodules true
deploy_to "/var/www"
current_path "/var/www/current"
recipe_name "api"
revision "HEAD"
scm_provider Chef::Provider::Git
purge_before_symlink ["log", "tmp/pids", "public/system"]
git_ssh_wrapper "/var/www/git-ssh-wrapper"
remote "origin"
shared_path "/var/www/shared"
cookbook_name "kapture"
symlinks {"log"=>"log", "system"=>"public/system", "pids"=>"tmp/pids"}
action [:deploy]
repo "git#github.com:kapture/api.git"
retry_delay 2
end
[2012-09-24T15:42:07+00:00] ERROR: Running exception handlers
[2012-09-24T15:42:07+00:00] FATAL: Saving node information to /var/chef/cache/failed-run-data.json
[2012-09-24T15:42:07+00:00] ERROR: Exception handlers complete
[2012-09-24T15:42:07+00:00] FATAL: Stacktrace dumped to /var/chef/cache/chef-stacktrace.out
[2012-09-24T15:42:07+00:00] FATAL: Chef::Exceptions::FileNotFound: deploy_revision[/var/www] (kapture::api line 69) had an error: Chef::Exceptions::FileNotFound: Cannot symlink /var/www/shared/config/database.yml to /var/www/releases/7404041cf8859a35de90ae72091bea1628391075/config/database.yml before migrate: No such file or directory - /var/www/shared/config/database.yml or /var/www/releases/7404041cf8859a35de90ae72091bea1628391075/config/database.yml
Here you can see it mention database.yml, tmp/, system/ and pids folders, all of which are defaults that Chef likes to set (see related bug)
Question 1
What are these symlinks for and how do I know if I even need any. What sort of things am I symlinking? I will be using migrations, so if they are useful for the migration then I'll need them working.
I have read the documentation many times and it just doesn't explain this is plain English - at least not that I have found.
Question 2
If I do not require them, how can I disable symlinking entirely? Following the examples in that bug report have not helped.

Answer 1

Clear out all the symlink attributes.
deploy_revision("/var/www") do
# ...
symlink_before_migrate.clear
create_dirs_before_symlink.clear
purge_before_symlink.clear
symlinks.clear
end

Answer 2

Make sure the deployment directory in shared has the proper directory structure (/var/www/shared/[log,pids,system,config]) and that all config files necessary for your application are in the config directory.
Your recipe for your application's cookbook should have an array of directory names to create (recursively) so that you won't run into this error again.
The symlinks are there so that while your application code will continue to evolve, you can share the log, pids, and system folder by symlinking shared/log to current/log and so on and so forth..

Answer 3

Chef happens to cache the directory structure - somehow, I haven't dug into that - with this troll application cookbook. It's something in the deploy resource I believe - I never use that - but you can fix it by deleting the directory structure it creates in /var/derp or whatever. Also ensure your tmp directory is setup.
A couple reasons this may be an issue:
File permissions are incorrect
The currently running chef user cannot access the file
You are using the application cookbook in a configuration for rails deploys and your application does not have the same directory structure.
It's definitely caused by Chef caching the state of the deploy somewhere, then reading that state out of it's cache - wherever that is - and then reusing that. I would look at either the application cookbook to see for any persistance, and if you fail at finding it there, look in the deploy resource from chef itself.