I ran into this error when trying to upload today’s blog post:

You have already activated public_suffix 3.1.1, but your Gemfile requires public_suffix 5.0.3. Consider using bundle exec.

To fix this I took the message’s advice and switched to bundle exec instead of calling jekyll directly in my command: line in my noproxy.web.yml file:

@@ -3,7 +3,7 @@ version: '3'
 services:
   web:
     image: jekyll/jekyll:3.8
-    command: jekyll serve --force_polling --host 0.0.0.0 --drafts --future
+    command: bundle exec jekyll serve --force_polling --host 0.0.0.0 --drafts --future
     ports:
       - 4000:4000
     volumes:
@@ -12,7 +12,7 @@ services:

   prod:
     image: jekyll/builder:3.8
-    command: jekyll serve --force_polling --host 0.0.0.0 --port 4001 -d _prod
+    command: bundle exec jekyll serve --force_polling --host 0.0.0.0 --port 4001 -d _prod
     ports:
       - 4001:4001
     volumes:

This seems to have fixed the issue.