commit to push for fear of loss.

== background ==
DataSource Mode (dsmode) is present in many datasources in cloud-init.
dsmode was originally added to cloud-init to specify when this datasource
should be 'realized'.

cloud-init has 4 stages of boot.
 a.) cloud-init --local . network is guaranteed not present.
 b.) cloud-init (--network). network is guaranteed present.
 c.) cloud-config
 d.) cloud-init final

'init_modules' [1] are run "as early as possible".  And as such, are executed
in either 'a' or 'b' based on the datasource.  However, executing them means
that user-data has been fully consumed.  User-data and vendor-data may have
'#include http://...' which then rely on the network being present.  boothooks
are an example of the things run in init_modules.

The 'dsmode' was a way for a user to indicate that init_modules
should run at 'a' (dsmode=local) or 'b' (dsmode=net) directly.

Things were further confused when a datasource could provide networking
configuration.  Then, we needed to apply the networking config at 'a'
but if the user had provided boothooks that expected networking, then the
init_modules would need to be executed at 'b'.  The config drive datasource
hacked its way through this and applies networking if *it* detects it is
a new instance.

== Suggested Change ==
The plan is to 
 1. incorporate 'dsmode' into DataSource superclass
 2. make all existing datasources default to network
 3. apply any networking configuration from a datasource on first boot only
    apply_networking will always rename network devices when it runs.
    for bug 1579130.
 4. run init_modules at cloud-init (network) time frame unless datasource
    is 'local'.
 5. Datasources can provide a 'first_boot' method that will be called when
    a new instance_id is found.  This will allow the config drive's write_files
    to be applied once.

Over all, this will very much simplify things.  We'll no longer have
2 sources like DataSourceNoCloud and DataSourceNoCloudNet, but would just
have one source with a dsmode.

== Concerns ==
Some things have odd reliance on dsmode.  For example, OpenNebula's get_hostname
uses it to determine if it should do a lookup of an ip address.

== Bugs to fix here ==
http://pad.lv/1577982 ConfigDrive: cloud-init fails to configure network from network_data.json
http://pad.lv/1579130 need to support systemd.link renaming of devices in container 
http://pad.lv/1577844 Drop unnecessary blocking of all net udev rules 

1 files changed, 13 insertions, 10 deletions

diff --git a/cloudinit/helpers.py b/cloudinit/helpers.py
index 09d75e65..abfb0cbb 100644
--- a/cloudinit/helpers.py
+++ b/cloudinit/helpers.py
@@ -328,6 +328,7 @@ class Paths(object):
         self.cfgs = path_cfgs
         # Populate all the initial paths
         self.cloud_dir = path_cfgs.get('cloud_dir', '/var/lib/cloud')
+        self.run_dir = path_cfgs.get('run_dir', '/run/cloud-init')
         self.instance_link = os.path.join(self.cloud_dir, 'instance')
         self.boot_finished = os.path.join(self.instance_link, "boot-finished")
         self.upstart_conf_d = path_cfgs.get('upstart_dir')
@@ -349,26 +350,19 @@ class Paths(object):
             "data": "data",
             "vendordata_raw": "vendor-data.txt",
             "vendordata": "vendor-data.txt.i",
+            "instance_id": "instance-id",
         }
         # Set when a datasource becomes active
         self.datasource = ds
 
     # get_ipath_cur: get the current instance path for an item
     def get_ipath_cur(self, name=None):
-        ipath = self.instance_link
-        add_on = self.lookups.get(name)
-        if add_on:
-            ipath = os.path.join(ipath, add_on)
-        return ipath
+        return self._get_path(self.instance_link, name)
 
     # get_cpath : get the "clouddir" (/var/lib/cloud/<name>)
     # for a name in dirmap
     def get_cpath(self, name=None):
-        cpath = self.cloud_dir
-        add_on = self.lookups.get(name)
-        if add_on:
-            cpath = os.path.join(cpath, add_on)
-        return cpath
+        return self._get_path(self.cloud_dir, name)
 
     # _get_ipath : get the instance path for a name in pathmap
     # (/var/lib/cloud/instances/<instance>/<name>)
@@ -397,6 +391,15 @@ class Paths(object):
         else:
             return ipath
 
+    def _get_path(self, base, name=None):
+        add_on = self.lookups.get(name)
+        if not add_on:
+            return base
+        return os.path.join(base, add_on)
+
+    def get_runpath(self, name=None):
+        return self._get_path(self.run_dir, name)
+
 
 # This config parser will not throw when sections don't exist
 # and you are setting values on those sections which is useful