Add runner management health check for /ping

Even though we can check the health of the runner management, we would like to ensure an external health check validates the availability of all required services.

app/controllers/ping_controller.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class PingController < ApplicationController
-  before_action :postgres_connected!
+  before_action :postgres_connected!, :runner_manager_healthy!
   after_action :verify_authorized, except: %i[index]
 
   def index
@@ -20,4 +20,11 @@ class PingController < ApplicationController
 
     raise ActiveRecord::ConnectionNotEstablished
   end
+
+  def runner_manager_healthy!
+    # any unhandled exception leads to a HTTP 500 response.
+    return if Runner.strategy_class.health == true
+
+    raise Runner::Error::InternalServerError
+  end
 end

lib/runner/strategy.rb

@@ -53,6 +53,10 @@ class Runner::Strategy
     raise NotImplementedError
   end
 
+  def self.health
+    raise NotImplementedError
+  end
+
   def self.release
     raise NotImplementedError
   end

lib/runner/strategy/docker_container_pool.rb

@@ -153,6 +153,16 @@ class Runner::Strategy::DockerContainerPool < Runner::Strategy
     end
   end
 
+  def self.health
+    url = "#{config[:url]}/ping"
+    response = Faraday.get(url)
+    JSON.parse(response.body)['message'] == 'Pong'
+  rescue Faraday::Error => e
+    raise Runner::Error::FaradayError.new("Request to DockerContainerPool failed: #{e.inspect}")
+  rescue JSON::ParserError => e
+    raise Runner::Error::UnexpectedResponse.new("DockerContainerPool returned invalid JSON: #{e.inspect}")
+  end
+
   def self.release
     url = "#{config[:url]}/docker_container_pool/dump_info"
     response = Faraday.get(url)

lib/runner/strategy/null.rb

@@ -45,6 +45,10 @@ class Runner::Strategy::Null < Runner::Strategy
 
   def self.config; end
 
+  def self.health
+    true
+  end
+
   def self.release
     'N/A'
   end

lib/runner/strategy/poseidon.rb

@@ -216,6 +216,22 @@ class Runner::Strategy::Poseidon < Runner::Strategy
     @config ||= CodeOcean::Config.new(:code_ocean).read[:runner_management] || {}
   end
 
+  def self.health
+    url = "#{config[:url]}/health"
+    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Checking health from #{url}" }
+    response = http_connection.get url
+    case response.status
+      when 204
+        true
+      else
+        raise Runner::Error::UnexpectedResponse.new("Poseidon sent unexpected response status code #{response.status}")
+    end
+  rescue Faraday::Error => e
+    raise Runner::Error::FaradayError.new("Request to Poseidon failed: #{e.inspect}")
+  ensure
+    Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Finished getting health information" }
+  end
+
   def self.release
     url = "#{config[:url]}/version"
     Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Getting release from #{url}" }