Optimize read-only middleware so that it does not consume as much CPU

In !15082, we changed the behavior of the middleware to call
`Rails.application.routes.recognize_path` whenever a new route arrived.
However, this can be a CPU-intensive task because Rails needs to allocate
memory and compile 850+ different regular expressions, which are complicated
in GitLab.

As a short-term fix, we can do a lightweight string match before
we do the heavier comparison.

Closes #40185, gitlab-com/infrastructure#3240

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/gitlab/middleware/read_only.rb b/lib/gitlab/middleware/read_only.rb
index 5e4932e4e57..dc77f737da8 100644
--- a/lib/gitlab/middleware/read_only.rb
+++ b/lib/gitlab/middleware/read_only.rb
@@ -74,10 +74,16 @@ module Gitlab
       end
 
       def grack_route
+        # Calling route_hash may be expensive. Only do it if we think there's a possible match
+        return false unless request.path.end_with?('.git/git-upload-pack')
+
         route_hash[:controller] == 'projects/git_http' && route_hash[:action] == 'git_upload_pack'
       end
 
       def lfs_route
+        # Calling route_hash may be expensive. Only do it if we think there's a possible match
+        return false unless request.path.end_with?('/info/lfs/objects/batch')
+
         route_hash[:controller] == 'projects/lfs_api' && route_hash[:action] == 'batch'
       end
     end