How to extend a vagrant plugin through Vagrantfile without changing the .rb file?

I have this scenario in Vagrant where I wanted to patch how the ansible is being installed on RHEL 8 (because of certain issues with absence of packages missing due to repository setup) using ansible_local plugin. So here's the thing. Instead, I wanted to use pip3 (though I know I can use pip using ansible_local module but still it errs after that due to absence of certain repository so I figure out a way to fix it).

In my Vagrantfile, I have these lines as such,

.....
      node.vm.provision "ansible_local" do |ansible|
        ansible.playbook = ansible_playbook
        ansible.verbose = true
        ansible.install = true
        ## Actually this line doesn't suffice my problem since it still errs as pip requires other packages. Please check the *.rb file below
        if i == 100
            ansible.install_mode = "pip"
            ansible.version = "2.9"
            #ansible.ansible_rpm_install = Foo
        end
      end
...
.....

But because using pip still fails, so I end up changing the file /opt/vagrant/embedded/gems/2.2.9/gems/vagrant-2.2.9/plugins/provisioners/ansible/cap/guest/redhat/ansible_install.rb and what I did is this way,


cap/guest/redhat/ansible_install.rb
require_relative "../facts"
require_relative "../pip/pip"

module VagrantPlugins
  module Ansible
    module Cap
      module Guest
        module RedHat
          module AnsibleInstall

            def self.ansible_install(machine, install_mode, ansible_version, pip_args, pip_install_cmd = "")
              case install_mode
              when :pip
                pip_setup machine, pip_install_cmd
                Pip::pip_install machine, "ansible", ansible_version, pip_args, true
              when :pip_args_only
                pip_setup machine, pip_install_cmd
                Pip::pip_install machine, "", "", pip_args, false
              else
                
                // My added part as a quick fix/solution
                if machine.config.vm.box == "generic/rhel8"
                   ansible_rpm_install_rhel8 machine
                elsif
                   ansible_rpm_install machine
                end
                
              end
            end

            private

            def self.ansible_rpm_install(machine)
              rpm_package_manager = Facts::rpm_package_manager(machine)

              epel = machine.communicate.execute "#{rpm_package_manager} repolist epel | grep -q epel", error_check: false
              if epel != 0
                machine.communicate.sudo 'sudo rpm -i https://dl.fedoraproject.org/pub/epel/epel-release-latest-`rpm -E %dist | sed -n \'s/.*el\([0-9]\).*/\1/p\'`.noarch.rpm'
              end
              machine.communicate.sudo "#{rpm_package_manager} -y --enablerepo=epel install ansible"
            end

            def self.pip_setup(machine, pip_install_cmd = "")
              rpm_package_manager = Facts::rpm_package_manager(machine)

              machine.communicate.sudo("#{rpm_package_manager} -y install curl gcc libffi-devel openssl-devel python-crypto python-devel python-setuptools")
              Pip::get_pip machine, pip_install_cmd
            end

            def self.pip_setup(machine, pip_install_cmd = "")
              rpm_package_manager = Facts::rpm_package_manager(machine)

              machine.communicate.sudo("#{rpm_package_manager} -y install curl gcc libffi-devel openssl-devel python-crypto python-devel python-setuptools")
              Pip::get_pip machine, pip_install_cmd
            end

            
            // My added part as a quick fix/solution
            def self.ansible_rpm_install_rhel8(machine)
              rpm_package_manager = Facts::rpm_package_manager(machine)

              epel = machine.communicate.execute "#{rpm_package_manager} repolist epel | grep -q epel", error_check: false
              if epel != 0
                machine.communicate.sudo 'sudo rpm -i https://dl.fedoraproject.org/pub/epel/epel-release-latest-`rpm -E %dist | sed -n \'s/.*el\([0-9]\).*/\1/p\'`.noarch.rpm'
              end
              machine.communicate.sudo "dnf -y update; dnf -y install python3 python3-pip; pip3 install ansible"
            end
            
            
          end
        end
      end
    end
  end
end

So I added a method self.ansible_rpm_install_rhel8(machine) and did an if..elsif as a solution when box name is "generic/rhel8". This works perfect actually on my end. However, I don't like this approach i.e. changing the file /opt/vagrant/embedded/gems/2.2.9/gems/vagrant-2.2.9/plugins/provisioners/ansible/cap/guest/redhat/ansible_install.rb because once it changes or version upgrades, this will be gone. Is there any better way that I can just do this only inside Vagrantfile such that perhaps overriding or extending the class itself? I have no idea how to do this.

Any ideas are welcome.

Thank you!

Solution

You can use multiple provisioning sections next one another which will be executed in the order as you defined them in your Vagrantfile.

Instead of patching a plugin, try to prepare your ansible execution accordingly.

Before executing the provisioning part for ansible, execute a shell provisioning as follows:

Vagrant.configure("2") do |node|

    # ...

    node.vm.provision :shell, path: "fix_repo_and_add_packages.sh"

    node.vm.provision "ansible_local" do |ansible|
        ansible.playbook = ansible_playbook
        ansible.verbose = true
        ansible.install = true
        ## Actually this line doesn't suffice my problem since it still errs as pip requires other packages. Please check the *.rb file below
        if i == 100
            ansible.install_mode = "pip"
            ansible.version = "2.9"
            #ansible.ansible_rpm_install = Foo
        end
    end

end

Your fix_repo_and_add_packages.sh contains the setup of the missing repos and here you can add packages as well.

For more information about shell provisioning, you can find in the doc