Prevent admins from attempting hashed storage migration on read only DB

changelogs/unreleased/mk-avoid-read-only-error.yml

+---
+title: Prevent admins from attempting hashed storage migration on read only DB
+merge_request: 23597
+author:
+type: fixed

lib/tasks/gitlab/storage.rake

@@ -2,6 +2,12 @@ namespace :gitlab do
   namespace :storage do
     desc 'GitLab | Storage | Migrate existing projects to Hashed Storage'
     task migrate_to_hashed: :environment do
+      if Gitlab::Database.read_only?
+        warn 'This task requires database write access. Exiting.'
+
+        next
+      end
+
       storage_migrator = Gitlab::HashedStorage::Migrator.new
       helper = Gitlab::HashedStorage::RakeHelper
 
@@ -9,7 +15,7 @@ namespace :gitlab do
         project = Project.with_unmigrated_storage.find_by(id: helper.range_from)
 
         unless project
-          puts "There are no projects requiring storage migration with ID=#{helper.range_from}"
+          warn "There are no projects requiring storage migration with ID=#{helper.range_from}"
 
           next
         end
@@ -23,7 +29,7 @@ namespace :gitlab do
       legacy_projects_count = Project.with_unmigrated_storage.count
 
       if legacy_projects_count == 0
-        puts 'There are no projects requiring storage migration. Nothing to do!'
+        warn 'There are no projects requiring storage migration. Nothing to do!'
 
         next
       end

spec/tasks/gitlab/storage_rake_spec.rb

@@ -46,6 +46,16 @@ describe 'rake gitlab:storage:*' do
   describe 'gitlab:storage:migrate_to_hashed' do
     let(:task) { 'gitlab:storage:migrate_to_hashed' }
 
+    context 'read-only database' do
+      it 'does nothing' do
+        expect(Gitlab::Database).to receive(:read_only?).and_return(true)
+
+        expect(Project).not_to receive(:with_unmigrated_storage)
+
+        expect { run_rake_task(task) }.to output(/This task requires database write access. Exiting./).to_stderr
+      end
+    end
+
     context '0 legacy projects' do
       it 'does nothing' do
         expect(StorageMigratorWorker).not_to receive(:perform_async)
@@ -92,7 +102,7 @@ describe 'rake gitlab:storage:*' do
         stub_env('ID_FROM', 99999)
         stub_env('ID_TO', 99999)
 
-        expect { run_rake_task(task) }.to output(/There are no projects requiring storage migration with ID=99999/).to_stdout
+        expect { run_rake_task(task) }.to output(/There are no projects requiring storage migration with ID=99999/).to_stderr
       end
 
       it 'displays a message when project exists but its already migrated' do
@@ -100,7 +110,7 @@ describe 'rake gitlab:storage:*' do
         stub_env('ID_FROM', project.id)
         stub_env('ID_TO', project.id)
 
-        expect { run_rake_task(task) }.to output(/There are no projects requiring storage migration with ID=#{project.id}/).to_stdout
+        expect { run_rake_task(task) }.to output(/There are no projects requiring storage migration with ID=#{project.id}/).to_stderr
       end
 
       it 'enqueues migration when project can be found' do