I did some smoke testing of this, and it seems like there is still work to do.

Doing a 'restart juju-machine-agent' on a machine, I got this:

2012-02-21 23:35:40,411:1524(0xb7108b70):ZOO_INFO@check_events@1632: session establishment complete on server [10.207.38.151:2181], se
ssionId=0x135a23c31a5000a, negotiated timeout=10000
2012-02-21 23:35:40,424: juju.agents.machine@DEBUG: Units changed old:set([]) new:set(['mysql/0'])
2012-02-21 23:35:40,424: juju.agents.machine@DEBUG: Starting service unit: mysql/0 ...
2012-02-21 23:35:40,425: juju.agents.machine@INFO: Machine agent started id:1 deploy:<class 'juju.machine.unit.UnitMachineDeployment'>
 provider:'ec2'
2012-02-21 23:35:40,533: juju.agents.machine@DEBUG: Downloading charm local:oneiric/mysql-1329352875 to /var/lib/juju/charms
2012-02-21 23:35:41,061: juju.agents.machine@DEBUG: Starting service unit mysql/0
2012-02-21 23:35:42,247: juju.agents.machine@INFO: Started service unit mysql/0
2012-02-21 23:37:44,036:1524(0xb7108b70):ZOO_WARN@zookeeper_interest@1461: Exceeded deadline by 26ms
2012-02-21 23:37:47,385:1524(0xb7108b70):ZOO_WARN@zookeeper_interest@1461: Exceeded deadline by 15ms
2012-02-21 23:37:50,739:1524(0xb7108b70):ZOO_WARN@zookeeper_interest@1461: Exceeded deadline by 19ms
2012-02-21 23:58:38,875:1524(0xb7108b70):ZOO_WARN@zookeeper_interest@1461: Exceeded deadline by 19ms
2012-02-22 00:00:43,114:1524(0xb736d6c0):ZOO_INFO@zookeeper_close@2304: Closing zookeeper sessionId=0x135a23c31a5000a to [10.207.38.151:2181]

2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.3
2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@log_env@662: Client environment:host.name=domU-12-31-39-09-F0-F6
2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@log_env@669: Client environment:os.name=Linux
2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@log_env@670: Client environment:os.arch=3.0.0-14-virtual
2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@log_env@671: Client environment:os.version=#23-Ubuntu SMP Mon Nov 21 23:40:55 UTC 2011
2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@log_env@679: Client environment:user.name=(null)
2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@log_env@687: Client environment:user.home=/root
2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@log_env@699: Client environment:user.dir=/
2012-02-22 00:00:43,901:3654(0xb74f76c0):ZOO_INFO@zookeeper_init@727: Initiating client connection, host=domU-12-31-39-15-25-69.compute-1.internal:2181 sessionTimeout=10000 watcher=0xb730e5c0 sessionId=0 sessionPasswd=<null> context=0x8d62028 flags=0
2012-02-22 00:00:43,903:3654(0xb7294b70):ZOO_INFO@check_events@1585: initiated connection to server [10.207.38.151:2181]
2012-02-22 00:00:43,907:3654(0xb7294b70):ZOO_INFO@check_events@1632: session establishment complete on server [10.207.38.151:2181], sessionId=0x135a23c31a5000d, negotiated timeout=10000
2012-02-22 00:00:43,918: juju.agents.machine@DEBUG: Units changed old:set([]) new:set(['mysql/0'])
2012-02-22 00:00:43,918: juju.agents.machine@DEBUG: Starting service unit: mysql/0 ...
2012-02-22 00:00:43,918: juju.agents.machine@INFO: Machine agent started id:1 deploy:<class 'juju.machine.unit.UnitMachineDeployment'> provider:'ec2'
2012-02-22 00:00:43,984: juju.agents.machine@DEBUG: Downloading charm local:oneiric/mysql-1329352875 to /var/lib/juju/charms


Seems odd that it would download the mysql charm again.

Restarting the unit agent was a bit bizarre too, I don't see why config-changed was run:

2012-02-22 06:14:20,149: unit.lifecycle@DEBUG: pre-stop acquire, running:True
2012-02-22 06:14:20,150: unit.lifecycle@DEBUG: stopping relation lifecycles
2012-02-22 06:14:20,150: unit.lifecycle@DEBUG: stopped unit lifecycle
2012-02-22 06:14:20,150: hook.executor@DEBUG: stopped
2012-02-22 06:14:20,196:3576(0xb74506c0):ZOO_INFO@zookeeper_close@2304: Closing zookeeper sessionId=0x135a23c31a5000c to [10.207.38.151:2181]

2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.3
2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@log_env@662: Client environment:host.name=domU-12-31-39-09-F0-F6
2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@log_env@669: Client environment:os.name=Linux
2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@log_env@670: Client environment:os.arch=3.0.0-14-virtual
2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@log_env@671: Client environment:os.version=#23-Ubuntu SMP Mon Nov 21 23:40:55 UTC 2011
2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@log_env@679: Client environment:user.name=(null)
2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@log_env@687: Client environment:user.home=/root
2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@log_env@699: Client environment:user.dir=/
2012-02-22 06:14:20,932:3997(0xb73796c0):ZOO_INFO@zookeeper_init@727: Initiating client connection, host=domU-12-31-39-15-25-69.compute-1.internal:2181 sessionTimeout=10000 watcher=0xb71de5c0 sessionId=0 sessionPasswd=<null> context=0x9c63718 flags=0
2012-02-22 06:14:20,958:3997(0xb7116b70):ZOO_INFO@check_events@1585: initiated connection to server [10.207.38.151:2181]
2012-02-22 06:14:20,961:3997(0xb7116b70):ZOO_INFO@check_events@1632: session establishment complete on server [10.207.38.151:2181], sessionId=0x135a23c31a50011, negotiated timeout=10000
2012-02-22 06:14:21,057: hook.executor@DEBUG: started
2012-02-22 06:14:21,057: unit.lifecycle@DEBUG: pre-start acquire, running:False
2012-02-22 06:14:21,057: unit.lifecycle@DEBUG: start running, unit lifecycle
2012-02-22 06:14:21,058: unit.lifecycle@DEBUG: starting service relation watch
2012-02-22 06:14:21,058: unit.lifecycle@DEBUG: starting unit relation resolved watch
2012-02-22 06:14:21,059: unit.lifecycle@DEBUG: relation resolved changed
2012-02-22 06:14:21,059: unit.lifecycle@INFO: processing relation resolved changed
2012-02-22 06:14:21,062: unit.lifecycle@DEBUG: services changed old:None new:[]
2012-02-22 06:14:21,062: unit.lifecycle@DEBUG: processing relations changed
2012-02-22 06:14:21,063: unit.lifecycle@DEBUG: started unit lifecycle
2012-02-22 06:14:21,067: juju.agents.unit@DEBUG: Configuration Changed
2012-02-22 06:14:21,075: statemachine@DEBUG: unitworkflowstate: transition configure (started -> started) {}
2012-02-22 06:14:21,075: statemachine@DEBUG: unitworkflowstate:  execute action do_configure
2012-02-22 06:14:21,075: hook.executor@DEBUG: Running hook: /var/lib/juju/units/mysql-0/charm/hooks/config-changed
2012-02-22 06:14:22,250: unit.hook.api@INFO: my.cnf not changed, skipping restart/replace
2012-02-22 06:14:22,251: hook.output@INFO: {}

2012-02-22 06:14:22,267: hook.output@DEBUG: hook config-changed exited, exit code 0.
2012-02-22 06:14:22,276: hook.executor@DEBUG: Hook complete: /var/lib/juju/units/mysql-0/charm/hooks/config-changed
2012-02-22 06:14:22,276: unit.lifecycle@DEBUG: configured unit
2012-02-22 06:14:22,295: statemachine@DEBUG: unitworkflowstate: transition complete configure (state started) {}
2012-02-22 06:14:22,298: juju.agents.unit@INFO: No upgrade flag set.

Rebooting worked in much the same manner. Its important to note that the reboot only took about 24 seconds...

2012-02-22 06:15:56,635:3997(0xb73796c0):ZOO_INFO@zookeeper_close@2304: Closing zookeeper sessionId=0x135a23c31a50011 to [10.207.38.151:2181]
2012-02-22 06:16:32,669:602(0xb735f6c0):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.3

When I stopped the instance, and ran juju status, I got an ERROR, which I think is erroneous, and should probably just be indicated with instance-state and running:

2012-02-21 22:28:09,940 INFO Connecting to environment...
2012-02-21 22:28:14,727 INFO Connected to environment.
2012-02-21 22:28:18,952 ERROR Machine provider information missing: machine 1
machines:
  0:
    dns-name: ec2-50-19-20-85.compute-1.amazonaws.com
    instance-id: i-bc7277d9
    instance-state: running
    state: running
  1:
    instance-id: i-be1712db
services:
  mysql:
    charm: local:oneiric/mysql-1329352875
    relations: {}
    units:
      mysql/0:
        machine: 1
        public-address: ec2-50-17-61-47.compute-1.amazonaws.com
        relations: {}
        state: down
2012-02-21 22:28:18,958 INFO 'status' command finished successfully

After leaving it off for 3 minutes, I started it back up, and had no problems:

2012-02-22 06:25:41,999:577(0xb73606c0):ZOO_INFO@zookeeper_close@2304: Closing zookeeper sessionId=0x135a23c31a50016 to [10.207.38.151:2181]
2012-02-22 06:28:58,070:574(0xb74f06c0):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.3

This included adding and removing relations.