Implement atomic deployments for Nulecule application. Fixes #421

When there's an error during running a Nulecule application,
rollback the changes made by stopping the application.

Author: rtnpro

atomicapp/nulecule/base.py

@@ -135,22 +135,23 @@ def run(self, provider_key=None, dryrun=False):
         for component in self.components:
             component.run(provider_key, dryrun)
 
-    def stop(self, provider_key=None, dryrun=False):
+    def stop(self, provider_key=None, dryrun=False, ignore_errors=False):
         """
         Stop the Nulecule application.
 
         Args:
             provider_key (str): Provider to use for running Nulecule
                                 application
             dryrun (bool): Do not make changes to host when True
+            ignore_errors (bool): Ignore errors, if any, when True
 
         Returns:
             None
         """
         provider_key, provider = self.get_provider(provider_key, dryrun)
         # stop the Nulecule application
         for component in self.components:
-            component.stop(provider_key, dryrun)
+            component.stop(provider_key, dryrun, ignore_errors)
 
     def uninstall(self):
         # uninstall the Nulecule application
@@ -264,7 +265,7 @@ def run(self, provider_key, dryrun=False):
         provider.init()
         provider.deploy()
 
-    def stop(self, provider_key=None, dryrun=False):
+    def stop(self, provider_key=None, dryrun=False, ignore_errors=False):
         """
         Stop the Nulecule component with the specified provider.
         """
@@ -274,7 +275,11 @@ def stop(self, provider_key=None, dryrun=False):
         provider_key, provider = self.get_provider(provider_key, dryrun)
         provider.artifacts = self.rendered_artifacts.get(provider_key, [])
         provider.init()
-        provider.undeploy()
+        try:
+            provider.undeploy()
+        except Exception as e:
+            if not ignore_errors:
+                raise e
 
     def load_config(self, config=None, ask=False, skip_asking=False):
         """

atomicapp/nulecule/main.py

@@ -192,7 +192,7 @@ def run(self, cli_provider, answers_output, ask,
 
         self.nulecule.load_config(config=self.nulecule.config, ask=ask)
         self.nulecule.render(cli_provider, dryrun)
-        self.nulecule.run(cli_provider, dryrun)
+
         runtime_answers = self._get_runtime_answers(
             self.nulecule.config, cli_provider)
         self._write_answers(
@@ -202,12 +202,21 @@ def run(self, cli_provider, answers_output, ask,
             self._write_answers(answers_output, runtime_answers,
                                 self.answers_format)
 
-    def stop(self, cli_provider, **kwargs):
+        try:
+            self.nulecule.run(cli_provider, dryrun)
+        except Exception as e:
+            logger.error('Application run error: %s' % e)
+            logger.debug('Nulecule run error: %s' % e, exc_info=True)
+            logger.info('Rolling back changes')
+            self.stop(cli_provider, ignore_errors=True, **kwargs)
+
+    def stop(self, cli_provider, ignore_errors=False, **kwargs):
         """
         Stops a running Nulecule application.
 
         Args:
             cli_provider (str): Provider running the Nulecule application
+            ignore_errors (bool): Ignore errors, if any, when True
             kwargs (dict): Extra keyword arguments
         """
         # For stop we use the generated answer file from the run
@@ -219,7 +228,7 @@ def stop(self, cli_provider, **kwargs):
             self.app_path, config=self.answers, dryrun=dryrun)
         self.nulecule.load_config(config=self.answers)
         self.nulecule.render(cli_provider, dryrun=dryrun)
-        self.nulecule.stop(cli_provider, dryrun)
+        self.nulecule.stop(cli_provider, dryrun, ignore_errors)
 
     def uninstall(self):
         # For future use