Milestone page with too many issues times out with 502 error

Summary

For milestones with many issues, the milestone page times out with a 502 status code.

Steps to reproduce

Attempt to visit https://gitlab.com/groups/gitlab-org/-/milestones/14.

What is the current bug behavior?

Requesting the page results in a 502 timeout response.

What is the expected correct behavior?

Requesting the page results in a 200 success or 304 no-change response.

Relevant logs and/or screenshots

• See some of the Sentry issues, one of the most recent being 1077330
• The Sentry issues imply the app/views/shared/milestones/_issuable.html.haml view partial is being loaded too many times.

Output of checks

This bug happens on GitLab.com.

Possible fixes

Limit the number of Issues displayed on the Milestones page, possibly using one of these strategies:

• Hard limit of N issues, with link to the issue "list" page (which uses pagination)
• Infinite scrolling
• Pagination