Chef - create template with dynamic variable?

Question

I'm having a bit of a challenge on a Chef recipe. I'm new to Chef, so please bear with me.

Step 1: My chef recipe installs Ruby Passenger, then compiles the Passenger nginx module along with Nginx.

# Install passenger and nginx module
bash "Install Passenger" do
  code <<-EOF
  source /usr/local/rvm/scripts/rvm
  gem install passenger
  EOF
  user "root"
  not_if { `gem list`.lines.grep(/^passenger \(.*\)/).count > 0 }
end

# Install passenger
# Note that we have to explicitly include the RVM script otherwise it won't setup the environment correctly
bash "Install passenger nginx module and nginx from source" do
  code <<-EOF
  source /usr/local/rvm/scripts/rvm
  passenger-install-nginx-module --auto --prefix=/opt/nginx --auto-download
  EOF
  user "root"
  not_if { File.directory? "/opt/nginx" }
end

Step 2: After that, I create the nginx config file using a template. This configuration requires the location of Passenger, which is dependent on step 1 completing.

template "/opt/nginx/conf/nginx.conf" do
  source "nginx.conf.erb"
  action :create
  variables(
    deploy_user: deploy_user,
    passenger_root: `bash -c "source /usr/local/rvm/scripts/rvm; passenger-config --root"`.chomp,
    passenger_ruby: `bash -c "source /usr/local/rvm/scripts/rvm; which ruby"`.chomp,
    passenger: node[:passenger]
  )
end

Problem: Chef appears to compile templates at th ebeginning of the run. So what ends up happening is that Step 2 is actually compiled before Step 1 is run. This means that the passenger_root variable is blank. It needs Step 1 to complete before being able to get the passenger_root, then run the template.

I tried wrapping the step 2 code in a ruby_block but that doesn't work: undefined methodtemplate' for Chef::Resource::RubyBlock`.

Not sure what to do here, or what is the best practice for Chef for something like this?

Thanks in advance,

Leonard

Answer 1

A cleaner and recommended way is to use Lazy Attribute Evaluation.

template "/opt/nginx/conf/nginx.conf" do
  source "nginx.conf.erb"
  action :create
  variables lazy {
    { 
      deploy_user: deploy_user,
      passenger_root: `bash -c "source /usr/local/rvm/scripts/rvm; passenger-config --root"`.strip,
      passenger_ruby: `bash -c "source /usr/local/rvm/scripts/rvm; which ruby"`.strip,
      passenger: node[:passenger]
    }
  }
end

Also, I'd suggest using strip instead of chomp [thanks Draco].