Add health check information to Puma migration docs
A change in behavior in how Unicorn and Puma restart, means it is important for our customers to ensure they are adding the Puma healthcheck to their load balancer settings.
This will help to prevent any requests from failing while an update is being rolled out across the fleet. This is required because when the Puma service restarts there is a period of time where it will not handle any requests (unlike Unicorn).
Content to document
- Change in behavior during a restart
- What healthcheck to use -
/readiness
? - Recommend polling intervals and delays - https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/8074#note_233258949?