After my latest update to Gitlab (to version 10.7.3 ee), I found my webhooks on several of my repositories stopped working.  When I’d manually test them from the Gitlab Interface, I got a generic 500 error:

I figured this had something to do with the recent update, so I dug into the logs.  I found the issue in /var/log/gitlab/gitlab-rails/production.log:

Gitlab::HTTP::BlockedUrlError (URL ‘https://myserver.domain.com:8170/code-manager/v1/webhook?type=github&token=blahblahblahblah’ is blocked: Requests to the local network
are not allowed):
lib/gitlab/proxy_http_connection_adapter.rb:17:in `rescue in connection’
lib/gitlab/proxy_http_connection_adapter.rb:14:in `connection’
app/services/web_hook_service.rb:73:in `make_request’
app/services/web_hook_service.rb:26:in `execute’
app/models/hooks/web_hook.rb:10:in `execute’
app/services/test_hooks/base_service.rb:22:in `block in execute’
app/services/test_hooks/base_service.rb:19:in `catch’
app/services/test_hooks/base_service.rb:19:in `execute’
app/controllers/projects/hooks_controller.rb:41:in `test’
lib/gitlab/i18n.rb:50:in `with_locale’
lib/gitlab/i18n.rb:56:in `with_user_locale’
app/controllers/application_controller.rb:334:in `set_locale’
lib/gitlab/middleware/multipart.rb:95:in `call’
lib/gitlab/request_profiler/middleware.rb:14:in `call’
ee/lib/gitlab/jira/middleware.rb:15:in `call’
lib/gitlab/middleware/go.rb:17:in `call’
lib/gitlab/etag_caching/middleware.rb:11:in `call’
lib/gitlab/middleware/read_only/controller.rb:28:in `call’
lib/gitlab/middleware/read_only.rb:16:in `call’
lib/gitlab/request_context.rb:18:in `call’
lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call’
lib/gitlab/middleware/release_env.rb:10:in `call’

The whole “requests to the local network are not allowed” thing was new to me, so I found this:

https://docs.gitlab.com/ee/user/project/integrations/webhooks.html

The comments at the bottom showed me the way.  THere is a new setting you have to enable:

1. Log into Gitlab
2. Go to the admin area
3. Go to Settings
4. Go to Outbound Requests
5. Click the “Allow requests to the local network from hooks and services” button.
6. Save the changes

Viola!  It works now.