core: retry SSH keygen on RSAError [GH-5056]

/cc @sethvargo

CHANGELOG.md

@@ -49,6 +49,7 @@ BUG FIXES:
   - core: Only take files when packaging a box to avoid duplicates [GH-5658, GH-5657]
   - core: escape curl urls and authentication [GH-5677]
   - core: fix crash if a value is missing for CLI arguments [GH-5550]
+  - core: retry SSH key generation for transient RSA errors [GH-5056]
   - core/cli: fix box checksum validation [GH-4665, GH-5221]
   - core/windows: allow Windows UNC paths to allow more than 256
       characters [GH-4815]

lib/vagrant/util/keypair.rb

@@ -1,9 +1,13 @@
 require "base64"
 require "openssl"
 
+require "vagrant/util/retryable"
+
 module Vagrant
   module Util
     class Keypair
+      extend Retryable
+
       # Creates an SSH keypair and returns it.
       #
       # @param [String] password Password for the key, or nil for no password.
@@ -11,7 +15,13 @@ module Vagrant
       #   respectively. The final element is the OpenSSH encoded public
       #   key.
       def self.create(password=nil)
-        rsa_key     = OpenSSL::PKey::RSA.new(2048)
+        # This sometimes fails with RSAError. It is inconsistent and strangely
+        # sleeps seem to fix it. We just retry this a few times. See GH-5056
+        rsa_key = nil
+        retryable(on: OpenSSL::PKey::RSAError, sleep: 2, tries: 5) do
+          rsa_key = OpenSSL::PKey::RSA.new(2048)
+        end
+
         public_key  = rsa_key.public_key
         private_key = rsa_key.to_pem