Add certs health check endpoint (LG-3929)

app/controllers/health/certs_controller.rb

@@ -0,0 +1,20 @@
+module Health
+  class CertsController < ApplicationController
+    newrelic_ignore_apdex
+
+    def index
+      deadline = params[:deadline].present? ? Time.zone.parse(params[:deadline]) : 30.days.from_now
+
+      result = health_checker.check_certs(deadline: deadline)
+
+      render json: result.as_json,
+             status: result.healthy? ? :ok : :service_unavailable
+    end
+
+    private
+
+    def health_checker
+      @health_checker ||= HealthChecker.new
+    end
+  end
+end

app/services/health_checker.rb

@@ -0,0 +1,39 @@
+class HealthChecker
+  Result = Struct.new(:healthy, :info, keyword_init: true) do
+    alias_method :healthy?, :healthy
+  end
+
+  def initialize(certificates_store: CertificateStore.instance)
+    @certificates_store = certificates_store
+  end
+
+  # @param [Time] deadline
+  # @return [Result]
+  def check_certs(deadline:)
+    expiring_certs = certificates_store.select do |cert|
+      cert.expired?(deadline)
+    end
+
+    Result.new(
+      healthy: expiring_certs.empty?,
+      info: {
+        deadline: deadline,
+        expiring: expiring_certs.sort_by(&:not_after).map { |cert| cert_info(cert) },
+      }
+    )
+  end
+
+  private
+
+  attr_reader :certificates_store
+
+  # @param [Certificate] cert
+  def cert_info(cert)
+    {
+      expiration: cert.not_after,
+      subject: cert.subject.to_s,
+      issuer: cert.issuer.to_s,
+      key_id: cert.key_id,
+    }
+  end
+end

config/routes.rb

@@ -2,4 +2,6 @@
   # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
   get '/', to: 'identify#create'
   post '/', to: 'verify#open'
+
+  get '/api/health/certs' => 'health/certs#index'
 end

spec/controllers/health/certs_controller_spec.rb

@@ -0,0 +1,61 @@
+require 'rails_helper'
+
+RSpec.describe Health::CertsController do
+  describe '#index' do
+    subject(:action) { get :index, params: { deadline: deadline } }
+    let(:deadline) { nil }
+    let(:health_checker) { HealthChecker.new(certificates_store: certificates_store) }
+
+    before do
+      allow(controller).to receive(:health_checker).and_return(health_checker)
+    end
+
+    let(:expiring_cert) do
+      instance_double(
+        'Certificate',
+        expired?: true,
+        not_after: 15.days.from_now,
+        subject: OpenSSL::X509::Name.new([%w[CN cert1], %w[OU example]]),
+        issuer: OpenSSL::X509::Name.new([%w[CN issuer1], %w[OU example]]),
+        key_id: 'ab:cd:ef:gh:jk'
+      )
+    end
+
+    context 'with expiring certs' do
+      let(:certificates_store) { [expiring_cert] }
+
+      it 'returns a 503' do
+        action
+
+        expect(response.status).to eq(503)
+
+        body = JSON.parse(response.body, symbolize_names: true)
+        expect(body).to include(healthy: false)
+        expect(body[:info][:expiring].first[:key_id]).to eq(expiring_cert.key_id)
+      end
+    end
+
+    context 'with no expiring certs' do
+      let(:certificates_store) { [] }
+
+      it 'returns a 200' do
+        action
+
+        expect(response.status).to eq(200)
+        expect(JSON.parse(response.body, symbolize_names: true)).to include(healthy: true)
+      end
+
+      context 'with a deadline param' do
+        let(:deadline) { '2020-01-01' }
+
+        it 'checks certs with that deadline' do
+          expect(health_checker).to receive(:check_certs).
+            with(deadline: Time.zone.parse(deadline)).
+            and_call_original
+
+          action
+        end
+      end
+    end
+  end
+end

spec/services/health_checker_spec.rb

@@ -0,0 +1,62 @@
+require 'rails_helper'
+
+RSpec.describe HealthChecker do
+  describe '#check_certs' do
+    subject(:health_checker) { HealthChecker.new(certificates_store: certificates_store) }
+    let(:deadline) { 30.days.from_now }
+
+    let(:expiring_cert) do
+      instance_double(
+        'Certificate',
+        expired?: true,
+        not_after: 15.days.from_now,
+        subject: OpenSSL::X509::Name.new([%w[CN cert1], %w[OU example]]),
+        issuer: OpenSSL::X509::Name.new([%w[CN issuer1], %w[OU example]]),
+        key_id: 'ab:cd:ef:gh:jk'
+      )
+    end
+
+    let(:not_expiring_cert) do
+      instance_double(
+        'Certificate',
+        expired?: false,
+        not_after: 45.days.from_now,
+        subject: OpenSSL::X509::Name.new([%w[CN cert2], %w[OU example]]),
+        issuer: OpenSSL::X509::Name.new([%w[CN issuer2], %w[OU example]]),
+        key_id: 'lm:no:pq:rs:tu'
+      )
+    end
+
+    context 'with certs that expire before the deadline' do
+      let(:certificates_store) { [expiring_cert, not_expiring_cert] }
+
+      it 'returns an unhealthy result with the expiring certs' do
+        result = health_checker.check_certs(deadline: deadline)
+
+        expect(result).to_not be_healthy
+        expect(result.info).to eq(
+          deadline: deadline,
+          expiring: [
+            {
+              expiration: expiring_cert.not_after,
+              subject: '/CN=cert1/OU=example',
+              issuer: '/CN=issuer1/OU=example',
+              key_id: expiring_cert.key_id,
+            },
+          ]
+        )
+      end
+    end
+
+    context 'with no certs that expire before the deadline' do
+      let(:certificates_store) { [not_expiring_cert] }
+
+      it 'returns a healthy result with no certs' do
+        result = health_checker.check_certs(deadline: deadline)
+
+        expect(result).to be_healthy
+        expect(result.info).to eq(deadline: deadline, expiring: [])
+      end
+    end
+  end
+end