Merge lp:~kim0/pyjuju/adding-hook-traces-to-readme-for-bashified-example into lp:pyjuju

[Ahmed Kamal]

Fixed docs to match hook changes (joined instead of changed) and new execution order

[Kapil Thangavelu (hazmat)]

Excerpts from Ahmed Kamal's message of Thu May 26 18:51:41 UTC 2011:
> Ahmed Kamal has proposed merging lp:~kim0/ensemble/adding-hook-traces-to-readme-for-bashified-example into lp:ensemble.
>
> Requested reviews:
> Ensemble Team (ensemble)
>
> For more details, see:
> https://code.launchpad.net/~kim0/ensemble/adding-hook-traces-to-readme-for-bashified-example/+merge/62537
>
> Fixed docs to match hook changes (joined instead of changed) and new execution order

Thanks again, for working on the documentation. Looks good but there are some errors in the traces.

There is no ensemble 'established' hook for relations. Instead we have joined called, all joines
are followed by a changed invocation (independent of if there is an actual change subsequent to
the join). All subsequent change invocations are due to changes in the related units.

[lp:~kim0/pyjuju/adding-hook-traces-to-readme-for-bashified-example]

188. By Ahmed Kamal on 2011-05-27

Updating hook trace, changed always gets fired after joined

[Ahmed Kamal (kim0)]

Just pushed fixed docs, let me know if that looks good

[William Reade (fwereade)]

I'd prefer it if there were a little more distinction between the explanatory comments and the actual hooks which are firing, but this is still useful information and I can't see any drawback to adding it.

review: Approve

[Clint Byrum (clint-fewbar)]

lgtm as well

review: Approve

[Clint Byrum (clint-fewbar)]

This was created before config-changed, I just realized. So it needs to be updated before merging to reflect when config-changed is run as well.

review: Needs Fixing

Unmerged revisions

188. By Ahmed Kamal on 2011-05-27

Updating hook trace, changed always gets fired after joined

187. By Ahmed Kamal on 2011-05-26

Fixing docs to match hook changes (joined)

186. By Ahmed Kamal on 2011-04-14

Adding a sample hook execution trace to readme to better understand execution dynamics

=== modified file 'examples/readme.txt'
--- examples/readme.txt	2011-02-23 19:08:28 +0000
+++ examples/readme.txt	2011-05-27 15:29:31 +0000
@@ -1,7 +1,6 @@
 Examples
 ========
 
-
 These are some example formulas that can be deployed together to create some connected services.
 
 Many more formulas of greater functionality and utility exist in the Principia project, which
@@ -9,7 +8,6 @@
 
 http://launchpad.net/principia
 
-
 Deploying
 =========
 
@@ -22,3 +20,35 @@
   $ ensemble status
 
 The status command will show the address of the newly deployed wordpress service.
+
+Hooks Triggering Sequence
+=========================
+
+To better understand the above deployment dynamics, let's trace through hook execution
+
+  $ ensemble deploy --repository=examples mysql
+  mysql/0(install)
+  mysql/0(start)
+  $ ensemble deploy --repository=examples wordpress
+  wordpress/0(install)
+  wordpress/0(start)
+  $ ensemble add-relation wordpress mysql
+  Two joined hooks are fired in parallel
+  wordpress/0(db-relation-joined): Hook doesn't exist, skipped
+  mysql/0(db-relation-joined): Does DB setup, might consume some time
+  After joined hooks, changed hooks always get fired regardless
+  wordpress/0(db-relation-changed): Hook finds out database is still being created, early exits
+  mysql/0(db-relation-changed): Hook doesn't exist, skipped
+  At end of mysql/0(db-relation-joined) relation-set is called, triggering a run of
+  wordpress/0(db-relation-changed): Read DB settings from relation, applies config
+
+Assuming another wordpress service unit is to be added
+  $ ensemble add-unit wordpress
+  wordpress/1(install)
+  wordpress/1(start)
+  Two joins in no particular order
+  wordpress/1(db-relation-joined): Hook doesn't exist, skipped
+  mysql/0(db-relation-joined): Hook detects DB already exists, does early exit
+  Two db-relation-changed in no particular order
+  mysql/0(db-relation-changed): Hook doesn't exist, skipped
+  wordpress/1(db-relation-changed): Read DB settings from relation, applies config