Deprecate and remove support for Redis 5

We've supported Redis 5 for a while, but we now ship and use Redis 6 now. We should deprecate support for Redis 5 like #327197 (closed)

Redis 7.0 (released on 2022-04-27) (2021-07/2021-09)

Redis 7.0 will be released in 2021-07 through 2021-09 was released on 2022-04-27, which deprecates Redis 5.2. So we had better drop support of Redis 5 around %15.2. If so, we can deprecate Redis 5 support around %15.2.

The team announced [...] they plan to increase the cadence of major Redis releases to two per year, with Redis 7.0 planned for Q3 of this year. [...]

https://redislabs.com/blog/top-9-takeaways-from-redisconf-2021/

Redis 5.x deprecation

Redis 5.0 through 5.2 reached it EOL on 2022-04-27:

Once version 3.0.0 replaces 2.2 as the latest stable, versions 2.0 and 2.2 are maintained, whereas version 1.x reaches its end of life. https://redis.io/docs/about/releases/

TODO

All milestones are temporary and Stretch.

%14.1

• Add CI Redis dependency 6.0: TODO
  • cf. #238216 (closed) and !52669 (merged)

%14.2

• Show warnings with rake gitlab:check that Redis 5 is outdated: TODO
  • cf. !59072 (merged) or !29395 (merged)
• Add Redis 5 deprecation to the coming release post: TODO
  • cf. gitlab-com/www-gitlab-com!79509 (merged) or gitlab-com/www-gitlab-com!45801 (merged)

%14.4

• Set the minimum version to 6 with rake gitlab:check that Redis 6 is not supported any more: TODO
  • cf. !62156 (merged)
• Update software requirements docs and README.md of gitlab-org/gitlab: TODO
  • cf. !62159 (merged)

%15.2

• Bump recommended Redis version from 5.0 to 6.0 !91646 (merged)
  • cf. !59072 (merged)

%15.3

• Add Redis 5.x deprecation notice
  • https://gitlab.com/gitlab-org/gitlab/-/blob/master/data/deprecations/templates/example.yml
  • Formerly needed to post to www-gitlab-com cf. gitlab-com/www-gitlab-com!79509 (merged)

%15.6

• Drop usage of Redis 5.0 from our CI
  • !102111 (closed)

%16.0

• Set the minimum version to 6.0 with rake gitlab:check that Redis 5 is not supported any more
  • !118448 (merged)
• Update minimum required Redis version in installation documentation.
  • !119224 (merged)
• Add changelog item item for Redis 5.x removal !119121 (merged)

Refs.

• Redis 4: #327197 (closed)
• Redis 3: #213174 (closed)