squashed - fix timing issues in prod importing projects

added changelog

fix specs

refactored code based on feedback

fix rubocop warning

CHANGELOG

@@ -41,6 +41,7 @@ v 8.10.3 (unreleased)
   - Fix hooks missing on imported GitLab projects
   - Properly abort a merge when merge conflicts occur
   - Ignore invalid IPs in X-Forwarded-For when trusted proxies are configured.
+  - Fix timing problems running imports on production
 
 v 8.10.2
   - User can now search branches by name. !5144

lib/gitlab/import_export/file_importer.rb

@@ -3,6 +3,8 @@ module Gitlab
     class FileImporter
       include Gitlab::ImportExport::CommandLineUtil
 
+      MAX_RETRIES = 8
+
       def self.import(*args)
         new(*args).import
       end
@@ -14,7 +16,10 @@ module Gitlab
 
       def import
         FileUtils.mkdir_p(@shared.export_path)
-        decompress_archive
+
+        wait_for_archived_file do
+          decompress_archive
+        end
       rescue => e
         @shared.error(e)
         false
@@ -22,6 +27,19 @@ module Gitlab
 
       private
 
+      # Exponentially sleep until I/O finishes copying the file
+      def wait_for_archived_file
+        MAX_RETRIES.times do |retry_number|
+          if File.exist?(@archive_file)
+            yield
+
+            break
+          else
+            sleep(2**retry_number)
+          end
+        end
+      end
+
       def decompress_archive
         result = untar_zxf(archive: @archive_file, dir: @shared.export_path)