Merge branch 'docs/geo-validation-tests' into 'master'

Add Geo validation tests docs page with initial content

Closes #214576

See merge request gitlab-org/gitlab!31270

doc/administration/geo/replication/geo_validation_tests.md

+# Geo validation tests
+
+The Geo team performs manual testing and validation on common deployment configurations to ensure that Geo works when upgrading between minor GitLab versions and major PostgreSQL database versions. This section contains a journal of recent validation tests and links to the relevant issues.
+
+## GitLab Upgrades
+
+### February 2020
+
+[Upgrade Geo HA installation](https://gitlab.com/gitlab-org/gitlab/-/issues/201837)
+
+- Description: Tested upgrading from GitLab 12.7.5 to the latest 12.8 package in a high availability configuration.
+- Outcome: Partial success because we did not run the looping pipeline during the demo to monitor downtime.
+
+### January 2020
+
+[Upgrade Geo HA installation](https://gitlab.com/gitlab-org/gitlab/-/issues/200085)
+
+- Description: Tested upgrading from GitLab 12.6.x to the latest 12.7 package in a high availability configuration.
+- Outcome: Upgrade test was successful.
+- Follow up issues:
+  - [Investigate Geo End to End Test Failures](https://gitlab.com/gitlab-org/gitlab/issues/201823)
+  - [Add More Logging to Geo End to End Tests](https://gitlab.com/gitlab-org/gitlab/issues/201830)
+  - [Excess Service Restarts During Zero-Downtime Upgrade](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5047)
+
+[Upgrade Geo HA installation](https://gitlab.com/gitlab-org/gitlab/-/issues/199836)
+
+- Description: Tested upgrading from GitLab 12.5.7 to 12.6.6 in a high availability configuration
+- Outcome: Upgrade test was successful.
+- Follow up issues:
+  - [Update docs for zero-downtime upgrades to ensure deploy node it not in-use](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5046)
+
+[Upgrade Geo HA installation](https://gitlab.com/gitlab-org/gitlab/-/issues/37044)
+
+- Description: Tested upgrading from GitLab 12.4.x to the latest 12.5 package in a high availability configuration.
+- Outcome: Upgrade test was successful.
+- Follow up issues:
+  - [Investigate why http push spec failed on primary node](https://gitlab.com/gitlab-org/gitlab/issues/199825)
+  - [Investigate if docs should be modified to include refresh foreign tables task](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5041)
+
+### October 2019
+
+[Upgrade Geo HA installation](https://gitlab.com/gitlab-org/gitlab/-/issues/35262)
+
+- Description: Tested uprgading from GitLab 12.3.5 to 12.4.1 in a high availability configuration.
+- Outcome: Upgrade test was successful.
+
+[Upgrade Geo HA installation](https://gitlab.com/gitlab-org/gitlab/-/issues/32437)
+
+- Description: Tested upgrading from GitLab 12.2.8 to 12.3.5
+- Outcome: Upgrade test was successful.
+
+[Upgrade Geo HA installation](https://gitlab.com/gitlab-org/gitlab/-/issues/32435)
+
+- Description: Tested upgrading from GitLab 12.1.9 to 12.2.8
+- Outcome: Partial success due to possible misconfiguration issues.
+
+## PostgreSQL Upgrades
+
+### April 2020
+
+[PostgreSQL 11 upgrade procedure for GEO installations](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/4975)
+
+- Description: Prior to making PostgreSQL 11 the default version of PG in GitLab 12.10, we tested upgrading to PG 11 in Geo deployments on GitLab 12.9.
+- Outcome: Partially successful. Issues were discovered in HA configurations with a separate tracking database and concerns were raised about allowing automatic upgrades when Geo enabled.
+- Follow up issues:
+  - [replicate-geo-database incorrectly tries to backup repos](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5241)
+  - [pg-upgrade fails to upgrade a standalone Geo tracking DB](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5242)
+  - [revert-pg-upgrade fails to downgrade a Geo secondary’s standalone tracking DB’s PG data](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5243)
+  - [Timeout error on Geo secondary read-replica near the end of `gitlab-ctl pg-upgrade`](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5235)
+
+[Verify GEO installation with PostgreSQL 11](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/4971)
+
+- Description: Prior to making PostgreSQL 11 the default version of PG in GitLab 12.10, we tested fresh installations of GitLab 12.9 with Geo, installed with PG 11.
+- Outcome: Installation test was successful.
+
+### September 2019
+
+[Test and validate PostgreSQL 10.0 upgrade for Geo](https://gitlab.com/gitlab-org/gitlab/issues/12092)
+
+- Description: With the 12.0 release, GitLab required an upgrade to PostgreSQL 10.0. We tested various upgrade scenarios from GitLab 11.11.5 through to 12.1.8.
+- Outcome: Multiple issues were found when upgrading and addressed in follow-up issues.
+- Follow up issues:
+  - [`gitlab-ctl` reconfigure fails on Redis node in HA Geo setup](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/4706)
+  - [HA with Geo upgrade from 12.0.9 to 12.1.9 does not upgrade PostgreSQL](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/4705)
+  - [refresh foreign tables fails on app server in HA setup after upgrade to 12.1.9](https://gitlab.com/gitlab-org/gitlab/-/issues/32119)