Make chef cookbook recipe only run once

Question

So I use the following recipe:

include_recipe "build-essential"

node_packages = value_for_platform(
  [ "debian", "ubuntu" ]                      => { "default" => [ "libssl-dev" ] },
  [ "amazon", "centos", "fedora", "centos" ]  => { "default" => [ "openssl-devel" ] },
  "default"   => [ "libssl-dev" ]
)

node_packages.each do |node_package|
  package node_package do
    action :install
  end
end

bash "install-node" do
  cwd Chef::Config[:file_cache_path]
  code <<-EOH
    tar -xzf node-v#{node["nodejs"]["version"]}.tar.gz
    (cd node-v#{node["nodejs"]["version"]} && ./configure --prefix=#{node["nodejs"]["dir"]} && make && make install)
  EOH
  action :nothing
  not_if "#{node["nodejs"]["dir"]}/bin/node --version 2>&1 | grep #{node["nodejs"]["version"]}"
end

remote_file "#{Chef::Config[:file_cache_path]}/node-v#{node["nodejs"]["version"]}.tar.gz" do
  source node["nodejs"]["url"]
  checksum node["nodejs"]["checksum"]
  notifies :run, resources(:bash => "install-node"), :immediately
end

It successfully installed nodejs on my Vagrant VM but on restart it's getting executed again. How do I prevent this? I'm not that good in reading ruby code.

Answer 1

To make the remote_file resource idempotent (i.e. to not download a file already present again) you have to correctly specify the checksum of the file. You do this in your code using the node["nodejs"]["checksum"] attribute. However, this only works, if the checksum is correctly specified as the SHA256 hash of the downloaded file, no other algorithm (esp. not MD5) is supported.

If the checksum is not correct, your recipe will still work. However, on the next run, Chef will notice that the checksum of the existing file is different from the one you specified and will download the file again, thus notify the install node ressource and do the whole compile stuff.