Health checks and reloads

[Aditya Umrani]

Hello,

We are using nginx plus and we use application health-checks. We want to
move to the 'mandatory' parameter which requires that servers pass the
health check before it becomes active.

Currently, we have a system which reloads all configs (rather than a diff
based system which would just only apply the changes via the APIs). It does
this by generating a new set of configs (routing rules, upstreams, etc) and
then calling reload on the parent (which essentially results in creating
new worker processes).

We are wondering what happens when nginx receives a reload. For an upstream
(for simplicity - say 1 host in that upstream) which is present in the old
config and is also present in the new config:
1. Will it block traffic till that host has successfully passed 'N' checks
(configured)
2. Will it return 502's as there are no more active hosts to serve for this
upstream.
3. Anything else?

Thanks,
Aditya
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