For Render port failure, try the previous way

production.Dockerfile

@@ -83,4 +83,5 @@ HEALTHCHECK --interval=5s --timeout=3s --start-period=0s --start-interval=5s --r
 
 # Start the server by default, this can be overwritten at runtime
 EXPOSE 3000
-CMD ["./bin/rails", "server"]
+# CMD ["./bin/rails", "server"]
+CMD ["bundle", "exec", "puma", "-C", "config/puma.rb"]

render.yaml

@@ -4,7 +4,6 @@ databases:
     user: mysite
     plan: free
 
-
 services:
   - type: web
     name: mysite