Add /-/readiness /-/liveness and /-/health_metrics endpoints to track application readiness

1 files changed, 60 insertions, 0 deletions

diff --git a/app/controllers/health_controller.rb b/app/controllers/health_controller.rb
new file mode 100644
index 00000000000..df0fc3132ed
--- /dev/null
+++ b/app/controllers/health_controller.rb
@@ -0,0 +1,60 @@
+class HealthController < ActionController::Base
+  protect_from_forgery with: :exception
+  include RequiresHealthToken
+
+  CHECKS = [
+    Gitlab::HealthChecks::DbCheck,
+    Gitlab::HealthChecks::RedisCheck,
+    Gitlab::HealthChecks::FsShardsCheck,
+  ].freeze
+
+  def readiness
+    results = CHECKS.map { |check| [check.name, check.readiness] }
+
+    render_check_results(results)
+  end
+
+  def liveness
+    results = CHECKS.map { |check| [check.name, check.liveness] }
+
+    render_check_results(results)
+  end
+
+  def metrics
+    results = CHECKS.flat_map(&:metrics)
+
+    response = results.map(&method(:metric_to_prom_line)).join("\n")
+
+    render text: response, content_type: 'text/plain; version=0.0.4'
+  end
+
+  private
+
+  def metric_to_prom_line(metric)
+    labels = metric.labels&.map { |key, value| "#{key}=\"#{value}\"" }&.join(',') || ''
+    if labels.empty?
+      "#{metric.name} #{metric.value}"
+    else
+      "#{metric.name}{#{labels}} #{metric.value}"
+    end
+  end
+
+  def render_check_results(results)
+    flattened = results.flat_map do |name, result|
+      if result.is_a?(Gitlab::HealthChecks::Result)
+        [[name, result]]
+      else
+        result.map { |r| [name, r] }
+      end
+    end
+    success = flattened.all? { |name, r| r.success }
+
+    response = flattened.map do |name, r|
+      info = { status: r.success ? 'ok' : 'failed' }
+      info['message'] = r.message if r.message
+      info[:labels] = r.labels if r.labels
+      [name, info]
+    end
+    render json: response.to_h, status: success ? :ok : :service_unavailable
+  end
+end