Commit 2e5f0b42 authored by Mac Newbold's avatar Mac Newbold
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Add a new page. Not linked in yet, but accessible as usual through...

Add a new page. Not linked in yet, but accessible as usual through docwrapper.php3?docname=states.html for those who know how.
parent 9e906611
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<center>
<h1>Emulab State Machines</h1>
</center>
<ul>
<li><b><a href="#nodeboot">Node Boot Process</a></b>
<p>
<li><b><a href="#exptstatus">Experiment Status</a></b>
<p>
<li><b><a href="#nodealloc">Node Allocation</a></b>
<p>
<li><b><a href="#userstatus">User Status</a></b>
</ul>
<hr>
<a name="nodeboot">
<h3>Node Boot Process</h3>
<img align="right" src="nodeboot.gif">
The node boot process shows the legal state transitions a node may
make during its cycle of rebooting. The NORMALv1 subgraph shows the
normal boot cycle. If a node starts out off, it is in the SHUTDOWN
state. When it is turned on, it moves to the BOOTING state, where it
contacts the Emulab server and gets its boottime configuration
information, and starts to load the operating system. In standard
Emulab disk images, as part of the OS startup, certain
testbed-specific scripts run, to perform node configuration. This is
done during the TBSETUP state. When the node has finished
initialization, it moves to the ISUP state. It may remain in this
state indefinitely before it shuts down again and returns to the
SHUTDOWN state to start the cycle over again. This machine is labeled
NORMALv1 because there will be other, more detailed versions of the
NORMAL machine that come in the near future, to better aid in error
recovery.
<p>
The MINIMAL machine shows what a minimally compliant custom operating
system image or kernal will do. Even an OS that doesn't support any
external interaction can use the MINIMAL machine. Emulab software is
responsable for seeing when nodes shut down and start booting, so in
the worst case, the node will cycle between SHUTDOWN and BOOTING. If
the custom OS supports ping replies, Emulab software will use ping to
infer when the node has moved to the ISUP state. In this way, an OS
without any Emulab-specific capabilities can comply with the state
machine transitions properly.
<p>
A special case of the normal boot process is the disk reloading
cycle. When we reload a disk, the node starts out in the SHUTDOWN
state. It then proceeds through the BOOTING, RELOADSETUP, RELOADING,
and RELOADDONE states as it performs the reloading tasks. This
granularity gives us the ability to perform appropriate error recovery
in a timely fashion while nodes are reloading.
<p>
The transitions shown between the different machines show how a node
can move from one machine or mode to another. A node that has been
shut down may be reconfigured to boot a different OS, so it may move
from NORMALv1 to MINIMAL mode, or vice versa. It may also be
reconfigured to reload its disk, and moves from NORMALv1 to
RELOAD. When the reload has completed, it moves back to NORMALv1
again. These are called Mode Transitions, and they define
relationships between machines that govern the same state data, in
this case the node boot status data.
<p>
<br clear="right">
<a name="exptstatus">
<h3>Experiment Status</h3>
<img align="right" src="exptstatus.gif">
<br clear="left">
The experiment status state machine shows the states that an Emulab
experiment may be in at any given time. Experiments always start as
NEW experiments. During PRERUN, they are loaded into the database, and
marked as SWAPPED, since they are currently swapped out. When an
experiment swapin is attempted, it moves to ACTIVATING. From there it
may find it cannot swap in, in which case it returns to SWAPPED. If it
succeeds it moves to the ACTIVE state until the experiment is swapped
out. It may also go to the TESTING state if it is running in test
mode, a special mode used by Emulab developers to test the Emulab
system itself. When it starts swapping out, the experiment moves to
the SWAPPING state, followed by the SWAPPED state. Because it has
returned to the SWAPPED state, it may proceed to activate again, or it
may be terminated. When termination starts, it moves to the
TERMINATING state, and then the TERMINATED state, where it may be
safely removed from the Emulab database.
<p>
<br clear="right">
<a name="nodealloc">
<h3>Node Allocation</h3>
<img align="right" src="nodealloc.gif">
The node allocation state machie also governs nodes, like the node
boot process, but instead of their boot status, it governs their
allocation status. A node that is not reserved and has a fresh copy of
the Emulab standard disk images starts in the FREE_CLEAN state. When
an experiment swaps in, it may reserve a node, and it moves to the
RESERVED state. When the experiment has finished using the node, it
may move to the REBOOT state, where it will be rebooted, to clear any
experimental configuration, or the RELOAD state, to refresh the disk
image to the standard version. If the node gets reloaded, it may move
the the FREE_CLEAN state. If it simply reboots, it moves to the
FREE_DIRTY state, meaning the disk may be "dirty", and not identical
to the standard image. A node in the FREE_DIRTY state may then be
reserved again, or may move to the RELOAD state prior to becoming a
FREE_CLEAN node. (FREE_DIRTY nodes are typically only reserved by
experiments in the same project as used them last.)
<p>
<br clear="right">
<a name="userstatus">
<h3>User Status</h3>
<img align="right" src="userstatus.gif">
The user status state machine shows the states a user's account may be
in at any given time. A user who applies for an account on Emulab
starts out as a NEWUSER. When they perform the email address
verification step, they become an UNAPPROVED user. When a project
leader approves them as a member of their project, they become an
ACTIVE user, and are granted the priviledges that normal users have on
Emulab. The actions they may perform depend on the access level they
were granted for each project in which they are a member. At any time
their account may be FROZEN, at which time their access is temporarily
suspended. They may be returned to ACTIVE status after being FROZEN. A
user account may safely be deleted in any state.
<p>
<br clear="right">
<hr>
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