Merge branch 'sh-simplify-liveness-check' into 'master'

Add /-/health basic health check endpoint

See merge request gitlab-org/gitlab-ce!20456

changelogs/unreleased/sh-simplify-liveness-check.yml

+---
+title: Add /-/health basic health check endpoint
+merge_request: 20456
+author:
+type: added

config/application.rb

@@ -154,6 +154,10 @@ module Gitlab
 
     config.action_view.sanitized_allowed_protocols = %w(smb)
 
+    # This middleware needs to precede ActiveRecord::QueryCache and other middlewares that
+    # connect to the database.
+    config.middleware.insert_after "Rails::Rack::Logger", "Gitlab::Middleware::BasicHealthCheck"
+
     config.middleware.insert_after Warden::Manager, Rack::Attack
 
     # Allow access to GitLab API from other domains

config/routes.rb

@@ -46,6 +46,7 @@ Rails.application.routes.draw do
   get 'health_check(/:checks)' => 'health_check#index', as: :health_check
 
   scope path: '-' do
+    # '/-/health' implemented by BasicHealthMiddleware
     get 'liveness' => 'health#liveness'
     get 'readiness' => 'health#readiness'
     post 'storage_check' => 'health#storage_check'

doc/user/admin_area/monitoring/health_check.md

@@ -20,14 +20,24 @@ To access monitoring resources, the client IP needs to be included in a whitelis
 
 [Read how to add IPs to a whitelist for the monitoring endpoints][admin].
 
-## Using the endpoint
+## Using the endpoints
 
 With default whitelist settings, the probes can be accessed from localhost:
 
+- `http://localhost/-/health`
 - `http://localhost/-/readiness`
 - `http://localhost/-/liveness`
 
-which will then provide a report of system health in JSON format.
+
+The first endpoint, `/-/health/`, only checks whether the application server is running. It does
+-not verify the database or other services are running. A successful response with return
+a 200 status code with the following message:
+
+```
+GitLab OK
+```
+
+The readiness and liveness probes will provide a report of system health in JSON format.
 
 Readiness example output:
 

lib/gitlab/middleware/basic_health_check.rb

+# frozen_string_literal: true
+
+# This middleware provides a health check that does not hit the database. Its purpose
+# is to notify the prober that the application server is handling requests, but a 200
+# response does not signify that the database or other services are ready.
+#
+# See https://thisdata.com/blog/making-a-rails-health-check-that-doesnt-hit-the-database/ for
+# more details.
+
+module Gitlab
+  module Middleware
+    class BasicHealthCheck
+      # This can't be frozen because Rails::Rack::Logger wraps the body
+      # rubocop:disable Style/MutableConstant
+      OK_RESPONSE = [200, { 'Content-Type' => 'text/plain' }, ["GitLab OK"]]
+      EMPTY_RESPONSE = [404, { 'Content-Type' => 'text/plain' }, [""]]
+      # rubocop:enable Style/MutableConstant
+      HEALTH_PATH = '/-/health'
+
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        return @app.call(env) unless env['PATH_INFO'] == HEALTH_PATH
+
+        request = Rack::Request.new(env)
+
+        return OK_RESPONSE if client_ip_whitelisted?(request)
+
+        EMPTY_RESPONSE
+      end
+
+      def client_ip_whitelisted?(request)
+        ip_whitelist.any? { |e| e.include?(request.ip) }
+      end
+
+      def ip_whitelist
+        @ip_whitelist ||= Settings.monitoring.ip_whitelist.map(&IPAddr.method(:new))
+      end
+    end
+  end
+end

spec/lib/gitlab/middleware/basic_health_check_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Middleware::BasicHealthCheck do
+  let(:app) { double(:app) }
+  let(:middleware) { described_class.new(app) }
+  let(:env) { {} }
+
+  describe '#call' do
+    context 'outside IP' do
+      before do
+        env['REMOTE_ADDR'] = '8.8.8.8'
+      end
+
+      it 'returns a 404' do
+        env['PATH_INFO'] = described_class::HEALTH_PATH
+
+        response = middleware.call(env)
+
+        expect(response[0]).to eq(404)
+      end
+
+      it 'forwards the call for other paths' do
+        env['PATH_INFO'] = '/'
+
+        expect(app).to receive(:call)
+
+        middleware.call(env)
+      end
+    end
+
+    context 'whitelisted IP' do
+      before do
+        env['REMOTE_ADDR'] = '127.0.0.1'
+      end
+
+      it 'returns 200 response when endpoint is hit' do
+        env['PATH_INFO'] = described_class::HEALTH_PATH
+
+        expect(app).not_to receive(:call)
+
+        response = middleware.call(env)
+
+        expect(response[0]).to eq(200)
+        expect(response[1]).to eq({ 'Content-Type' => 'text/plain' })
+        expect(response[2]).to eq(['GitLab OK'])
+      end
+
+      it 'forwards the call for other paths' do
+        env['PATH_INFO'] = '/-/readiness'
+
+        expect(app).to receive(:call)
+
+        middleware.call(env)
+      end
+    end
+  end
+end