Downsize 1 node of each sidekiq type, take 3

Production Change - Criticality 2 C2

Change Objective	Describe the objective of the change
Change Type	Type described above
Services Impacted	~"Service:Sidekiq"
Change Team Members	@ahmadsherif
Change Severity	C2
Buddy check	@andrewn
Tested in staging	Yes
Schedule of the change	2019-05-22
Duration of the change	15 minutes
Detailed steps for the change. Each step must include:	Described below

Terraform plan:

Terraform will perform the following actions:

  ~ module.sidekiq.google_compute_instance.sidekiq_asap[2]
      allow_stopping_for_update: "false" => "true"
      machine_type:              "n1-standard-8" => "custom-4-20480"

  ~ module.sidekiq.google_compute_instance.sidekiq_pages[2]
      allow_stopping_for_update: "" => "true"
      machine_type:              "n1-standard-8" => "n1-standard-4"

  ~ module.sidekiq.google_compute_instance.sidekiq_pipeline[2]
      allow_stopping_for_update: "" => "true"
      machine_type:              "n1-standard-8" => "n1-standard-4"

  ~ module.sidekiq.google_compute_instance.sidekiq_pullmirror[2]
      allow_stopping_for_update: "" => "true"
      machine_type:              "n1-standard-8" => "n1-standard-4"

  ~ module.sidekiq.google_compute_instance.sidekiq_realtime[2]
      allow_stopping_for_update: "false" => "true"
      machine_type:              "n1-highmem-16" => "n1-standard-8"


Plan: 0 to add, 5 to change, 0 to destroy.

Steps:

1. Run

   ssh sidekiq-asap-03-sv-gprd.c.gitlab-production.internal "sudo gitlab-ctl stop sidekiq-cluster"
   ssh sidekiq-pages-03-sv-gprd.c.gitlab-production.internal "sudo gitlab-ctl stop sidekiq-cluster"
   ssh sidekiq-pipeline-03-sv-gprd.c.gitlab-production.internal "sudo gitlab-ctl stop sidekiq-cluster"
   ssh sidekiq-pullmirror-03-sv-gprd.c.gitlab-production.internal "sudo gitlab-ctl stop sidekiq-cluster"
   ssh sidekiq-realtime-03-sv-gprd.c.gitlab-production.internal "sudo gitlab-ctl stop sidekiq-cluster"

2. Run

   tf apply -target="module.sidekiq.google_compute_instance.sidekiq_asap[2]" \
   -target="module.sidekiq.google_compute_instance.sidekiq_pages[2]" \
   -target="module.sidekiq.google_compute_instance.sidekiq_pipeline[2]" \
   -target="module.sidekiq.google_compute_instance.sidekiq_pullmirror[2]" \
   -target="module.sidekiq.google_compute_instance.sidekiq_realtime[2]"

Rollback:

1. Revert https://ops.gitlab.net/gitlab-com/gitlab-com-infrastructure/merge_requests/766
2. Run steps 1 & 2 from above