Merge lp:~bjornt/charms/precise/storage/multiple-units into lp:charms/storage

[Björn Tillenius]

Allow multiple storage units to work reliably.

Currently, the storage charm reads the block-device-path setting to get the path of the attached volume to mount. This is full of race conditions when you have multiple storage units, since that single setting is shared for all units. In practice, when you add a second storage unit, it will see the existing block-device-path setting for the first unit and try to mount it before any volume has been attached.

I've added a new relation setting, block-device-path-map, in lp:~bjornt/charms/trusty/block-storage-broker/multiple-units/. That works for multiple units. This branch will use it if exists, and if it doesn't, block-device-path is used as before. This ensures that using this branch with old versions of block-storage-broker won't break.

[Chris Glass (tribaal)]

That looks great, thanks a lot.

One little nitpick inline, then I'll go ahead and merge.

review: Approve

[lp:~bjornt/charms/precise/storage/multiple-units]

45. By Björn Tillenius on 2016-01-21

Typos.

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This item has failed automated testing! Results available here http://juju-ci.vapour.ws:8080/job/charm-bundle-test-lxc/2277/

review: Needs Fixing (automated testing)

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This item has failed automated testing! Results available here http://juju-ci.vapour.ws:8080/job/charm-bundle-test-aws/2256/

review: Needs Fixing (automated testing)

=== modified file 'hooks/storage-provider.d/block-storage-broker/block-storage-relation-changed'
--- hooks/storage-provider.d/block-storage-broker/block-storage-relation-changed	2015-08-24 20:21:07 +0000
+++ hooks/storage-provider.d/block-storage-broker/block-storage-relation-changed	2016-01-21 14:37:26 +0000
@@ -1,4 +1,5 @@
 #!/usr/bin/python
+import json
 
 import common_util
 import sys
@@ -50,5 +51,25 @@
 # data relation
 device_path = common_util._get_from_relation(
     "block-storage", "block-device-path")
+
+# Get the device path from block-device-path-map if it exists, since
+# that works when multiple storage units exist. Older versions of the
+# block-storage-broker charm don't set it, though.
+device_path_map = common_util._get_from_relation(
+    "block-storage", "block-device-path-map")
+if device_path_map is not None:
+    device_path_map = json.loads(device_path_map)
+    hookenv.log(
+        "Getting device_path from block-device-path-map. " +
+        repr(device_path_map))
+    device_path = device_path_map.get(instance_id)
+
+# Don't try to mount the volume before we set the instance id and the
+# block-storage-broker service gives us back the device path, indicating
+# that the volume has been attached.
+if not device_path:
+    hookenv.log("No block-device specified yet.")
+    sys.exit(0)
+
 common_util.mount_volume(device_path,  # Will wait for mountpoint
                          device_timeout=config_data.get('device_timeout'))