fix: database disconnect error when service not accessed frequently

Hopefully Closes: pact-foundation/pact_broker#138

pact_broker/database_connection.rb

@@ -16,5 +16,25 @@ def create_database_connection(logger)
     credentials[:port] = ENV['PACT_BROKER_DATABASE_PORT'].to_i
   end
 
-  Sequel.connect(credentials.merge(logger: DatabaseLogger.new(logger), encoding: 'utf8'))
+  ##
+  # Sequel by default does not test connections in its connection pool before
+  # handing them to a client. To enable connection testing you need to load the
+  # "connection_validator" extension like below. The connection validator
+  # extension is configurable, by default it only checks connections once per
+  # hour:
+  #
+  # http://sequel.rubyforge.org/rdoc-plugins/files/lib/sequel/extensions/connection_validator_rb.html
+  #
+  #
+  # A gotcha here is that it is not enough to enable the "connection_validator"
+  # extension, we also need to specify that we want to use the threaded connection
+  # pool, as noted in the documentation for the extension.
+  #
+  # -1 means that connections will be validated every time, which avoids errors
+  # when databases are restarted and connections are killed.  This has a performance
+  # penalty, so consider increasing this timeout if building a frequently accessed service.
+  connection = Sequel.connect(credentials.merge(logger: DatabaseLogger.new(logger), encoding: 'utf8'))
+  connection.extension(:connection_validator)
+  connection.pool.connection_validation_timeout = -1
+  connection
 end