Expose PostgreSQL load balancing options as global chart values

Summary

I'm using GitLab in Amazon EKS with an RDS Aurora PostgreSQL cluster for the database. While GitLab supports hot-standby load balancing (https://docs.gitlab.com/ee/administration/database_load_balancing.html), there is no way to configure it as part of the Helm charts.

Current behavior

globals.psql allows only a single host to be provided.

Expected behavior

globals.psql to have a loadbalancing section that allows multiple hosts to be specified.

Versions

• Chart: 1.3.0
• Platform:
  • Cloud: EKS
• Kubernetes: (kubectl version)
  • Client: version.Info{Major:"1", Minor:"10", GitVersion:"v1.10.3", GitCommit:"2bba0127d85d5a46ab4b778548be28623b32d0b0", GitTreeState:"clean", BuildDate:"2018-05-21T09:17:39Z", GoVersion:"go1.9.3", Compiler:"gc", Platform:"windows/amd64"}
  • Server: version.Info{Major:"1", Minor:"10+", GitVersion:"v1.10.11-eks", GitCommit:"6bf27214b7e3e1e47dce27dcbd73ee1b27adadd0", GitTreeState:"clean", BuildDate:"2018-12-04T13:33:10Z", GoVersion:"go1.9.3", Compiler:"gc", Platform:"linux/amd64"}
• Helm: (helm version)
  • Client: &version.Version{SemVer:"v2.11.0", GitCommit:"2e55dbe1fdb5fdb96b75ff144a339489417b146b", GitTreeState:"clean"}
  • Server: &version.Version{SemVer:"v2.11.0", GitCommit:"2e55dbe1fdb5fdb96b75ff144a339489417b146b", GitTreeState:"clean"}

Changes necessary

Per documentation of configuration:

1. Support configuration of global.psql.loadbalancing.(hosts|discover) through properties and templates into database.yml.
2. When using database load balancing, there is no supplied host or port. We need to ensure our charts can operate as such, when psql.loadbalancing is present / populated. This includes any fail or checkConfig patterns.
3. ☝ Interesting note, is that these don't seem to indicate a password 🤔
4. Logging of db load balancing is performed to yet another log file, in database_load_balancing.log. This must be added to

Documentation should be added or linked on how to setup the necessary environment for both "host based" load balancing, as well as "service discovery" based configurations. This may be most concisely done via gitlab-org/gitlab-orchestrator

• Add configuration properties and templating for global.psql.loadbalancing
• Ensure that database_load_balancing.log is added to various tail lists in CNG
• Add checkConfig to ensure that either host or loadbalancing.* is provided, when postgresql.install: false
• Add matching configuration properties and implementation for Geo Moved to #2164
• Document setting up a test environment, possibly add to docs/advanced