add the limit option, which can be used to further confine the patterns selected by "hosts:" in ansible-playbooks

to an additional pattern (a subset) specified on the command line.  For instance, a playbook could be reusable
and target "webservers" and "dbservers", but you want to test only in the stage environment, or a few boxes at a time.

CHANGELOG.md

@@ -28,6 +28,7 @@ Ansible Changes By Release
 * make remote_md5 internal function work with non-bash shells
 * allow user to be passed in via --extra-vars (regression)
 * add ability to store the result of any command in a register (see examples/playbooks/register_logic.yml)
+* add --limit option, which can be used to further confine the pattern given in ansible-playbooks
 
 0.6 "Cabo" -- August 6, 2012
 

bin/ansible-playbook

@@ -52,7 +52,7 @@ def main(args):
 
     # create parser for CLI options
     usage = "%prog playbook.yml"
-    parser = utils.base_parser(constants=C, usage=usage, connect_opts=True, runas_opts=True)
+    parser = utils.base_parser(constants=C, usage=usage, connect_opts=True, runas_opts=True, subset_opts=True)
     parser.add_option('-e', '--extra-vars', dest="extra_vars", default=None,
         help="set additional key=value variables from the CLI")
     parser.add_option('-t', '--tags', dest='tags', default='all',
@@ -102,6 +102,7 @@ def main(args):
             extra_vars=extra_vars,
             private_key_file=options.private_key_file,
             only_tags=only_tags,
+            subset=options.subset,
         )
         try:
 

lib/ansible/constants.py

@@ -35,4 +35,5 @@ DEFAULT_SUDO_USER      = os.environ.get('ANSIBLE_SUDO_USER','root')
 DEFAULT_REMOTE_PORT    = 22
 DEFAULT_TRANSPORT      = os.environ.get('ANSIBLE_TRANSPORT','paramiko')
 DEFAULT_TRANSPORT_OPTS = ['local', 'paramiko', 'ssh']
+DEFAULT_SUBSET         = None
 

lib/ansible/inventory/__init__.py

@@ -34,7 +34,7 @@ class Inventory(object):
     Host inventory for ansible.
     """
 
-    __slots__ = [ 'host_list', 'groups', '_restriction', '_is_script',
+    __slots__ = [ 'host_list', 'groups', '_restriction', '_subset', '_is_script',
                   'parser', '_vars_per_host', '_vars_per_group', '_hosts_cache' ]
 
     def __init__(self, host_list=C.DEFAULT_HOST_LIST):
@@ -55,6 +55,7 @@ class Inventory(object):
 
         # a list of host(names) to contain current inquiries to
         self._restriction = None
+        self._subset = None
 
         # whether the inventory file is a script
         self._is_script = False
@@ -103,7 +104,9 @@ class Inventory(object):
                 inverted = False
             for group in groups:
                 for host in group.get_hosts():
-                    if self._match(group.name, pat) or pat == 'all' or self._match(host.name, pat):
+                    if self._subset and host.name not in self._subset:
+                        continue
+                    if pat == 'all' or self._match(group.name, pat) or self._match(host.name, pat):
                         # must test explicitly for None because [] means no hosts allowed
                         if self._restriction==None or host.name in self._restriction:
                             if inverted:
@@ -187,12 +190,28 @@ class Inventory(object):
     def get_restriction(self):
         return self._restriction
 
-    def restrict_to(self, restriction, append_missing=False):
+    def restrict_to(self, restriction):
-        """ Restrict list operations to the hosts given in restriction """
+        """ 
+        Restrict list operations to the hosts given in restriction.  This is used
+        to exclude failed hosts in main playbook code, don't use this for other
+        reasons.
+        """
         if type(restriction) != list:
             restriction = [ restriction ]
         self._restriction = restriction
 
+    def subset(self, subset_pattern):
+        """ 
+        Limits inventory results to a subset of inventory that matches a given
+        pattern, such as to select a given geographic of numeric slice amongst
+        a previous 'hosts' selection that only select roles, or vice versa.  
+        Corresponds to --limit parameter to ansible-playbook
+        """        
+        if subset_pattern is None:
+            self._subset = None
+        else:
+            self._subset = self.list_hosts(subset_pattern)
+
     def lift_restriction(self):
         """ Do not restrict list operations """
 

lib/ansible/playbook/__init__.py

@@ -57,7 +57,8 @@ class PlayBook(object):
         sudo             = False,
         sudo_user        = C.DEFAULT_SUDO_USER,
         extra_vars       = None,
-        only_tags        = None):
+        only_tags        = None,
+        subset           = C.DEFAULT_SUBSET):
 
         """
         playbook:         path to a playbook file
@@ -105,6 +106,7 @@ class PlayBook(object):
         self.only_tags        = only_tags
 
         self.inventory        = ansible.inventory.Inventory(host_list)
+        self.inventory.subset(subset)
 
         if not self.inventory._is_script:
             self.global_vars.update(self.inventory.get_group_variables('all'))

lib/ansible/utils.py

@@ -336,7 +336,8 @@ def increment_debug(option, opt, value, parser):
     global VERBOSITY
     VERBOSITY += 1
 
-def base_parser(constants=C, usage="", output_opts=False, runas_opts=False, async_opts=False, connect_opts=False):
+def base_parser(constants=C, usage="", output_opts=False, runas_opts=False, 
+    async_opts=False, connect_opts=False, subset_opts=False):
     ''' create an options parser for any ansible script '''
 
     parser = SortedOptParser(usage, version=version("%prog"))
@@ -357,6 +358,11 @@ def base_parser(constants=C, usage="", output_opts=False, runas_opts=False, asyn
     parser.add_option('-M', '--module-path', dest='module_path',
         help="specify path(s) to module library (default=%s)" % constants.DEFAULT_MODULE_PATH,
         default=constants.DEFAULT_MODULE_PATH)
+
+    if subset_opts:
+        parser.add_option('-l', '--limit', default=constants.DEFAULT_SUBSET, dest='subset',
+            help='further limit selected hosts to an additional pattern')
+
     parser.add_option('-T', '--timeout', default=constants.DEFAULT_TIMEOUT, type='int',
         dest='timeout',
         help="override the SSH timeout in seconds (default=%s)" % constants.DEFAULT_TIMEOUT)