Synnefo » snf-ganeti

Ganeti walk-through

===================

Documents Ganeti version |version|

.. contents::

.. highlight:: shell-example

Introduction

------------

This document serves as a more example-oriented guide to Ganeti; while

the administration guide shows a conceptual approach, here you will find

a step-by-step example to managing instances and the cluster.

Our simulated, example cluster will have three machines, named

``node1``, ``node2``, ``node3``. Note that in real life machines will

usually have FQDNs but here we use short names for brevity. We will use

a secondary network for replication data, ``192.0.2.0/24``, with nodes

having the last octet the same as their index. The cluster name will be

``example-cluster``. All nodes have the same simulated hardware

configuration, two disks of 750GB, 32GB of memory and 4 CPUs.

On this cluster, we will create up to seven instances, named

``instance1`` to ``instance7``.

Cluster creation

----------------

Follow the :doc:`install` document and prepare the nodes. Then it's time

to initialise the cluster::

  $ gnt-cluster init -s %192.0.2.1% --enabled-hypervisors=xen-pvm %example-cluster%

  $

The creation was fine. Let's check that one node we have is functioning

correctly::

  $ gnt-node list

  Node  DTotal DFree MTotal MNode MFree Pinst Sinst

  node1   1.3T  1.3T  32.0G  1.0G 30.5G     0     0

  $ gnt-cluster verify

  Mon Oct 26 02:08:51 2009 * Verifying global settings

  Mon Oct 26 02:08:51 2009 * Gathering data (1 nodes)

  Mon Oct 26 02:08:52 2009 * Verifying node status

  Mon Oct 26 02:08:52 2009 * Verifying instance status

  Mon Oct 26 02:08:52 2009 * Verifying orphan volumes

  Mon Oct 26 02:08:52 2009 * Verifying remaining instances

  Mon Oct 26 02:08:52 2009 * Verifying N+1 Memory redundancy

  Mon Oct 26 02:08:52 2009 * Other Notes

  Mon Oct 26 02:08:52 2009 * Hooks Results

  $

Since this proceeded correctly, let's add the other two nodes::

  $ gnt-node add -s %192.0.2.2% %node2%

  -- WARNING --

  Performing this operation is going to replace the ssh daemon keypair

  on the target machine (node2) with the ones of the current one

  and grant full intra-cluster ssh root access to/from it

  Unable to verify hostkey of host xen-devi-5.fra.corp.google.com:

  f7:…. Do you want to accept it?

  y/[n]/?: %y%

  Mon Oct 26 02:11:53 2009  Authentication to node2 via public key failed, trying password

  root password:

  Mon Oct 26 02:11:54 2009  - INFO: Node will be a master candidate

  $ gnt-node add -s %192.0.2.3% %node3%

  -- WARNING --

  Performing this operation is going to replace the ssh daemon keypair

  on the target machine (node3) with the ones of the current one

  and grant full intra-cluster ssh root access to/from it

  …

  Mon Oct 26 02:12:43 2009  - INFO: Node will be a master candidate

Checking the cluster status again::

  $ gnt-node list

  Node  DTotal DFree MTotal MNode MFree Pinst Sinst

  node1   1.3T  1.3T  32.0G  1.0G 30.5G     0     0

  node2   1.3T  1.3T  32.0G  1.0G 30.5G     0     0

  node3   1.3T  1.3T  32.0G  1.0G 30.5G     0     0

  $ gnt-cluster verify

  Mon Oct 26 02:15:14 2009 * Verifying global settings

  Mon Oct 26 02:15:14 2009 * Gathering data (3 nodes)

  Mon Oct 26 02:15:16 2009 * Verifying node status

  Mon Oct 26 02:15:16 2009 * Verifying instance status

  Mon Oct 26 02:15:16 2009 * Verifying orphan volumes

  Mon Oct 26 02:15:16 2009 * Verifying remaining instances

  Mon Oct 26 02:15:16 2009 * Verifying N+1 Memory redundancy

  Mon Oct 26 02:15:16 2009 * Other Notes

  Mon Oct 26 02:15:16 2009 * Hooks Results

  $

And let's check that we have a valid OS::

  $ gnt-os list

  Name

  debootstrap

  node1#

Running a burn-in

-----------------

Now that the cluster is created, it is time to check that the hardware

works correctly, that the hypervisor can actually create instances,

etc. This is done via the debootstrap tool as described in the admin

guide. Similar output lines are replaced with ``…`` in the below log::

  $ /usr/lib/ganeti/tools/burnin -o debootstrap -p instance{1..5}

  - Testing global parameters

  - Creating instances

    * instance instance1

      on node1, node2

    * instance instance2

      on node2, node3

    …

    * instance instance5

      on node2, node3

    * Submitted job ID(s) 157, 158, 159, 160, 161

      waiting for job 157 for instance1

      …

      waiting for job 161 for instance5

  - Replacing disks on the same nodes

    * instance instance1

      run replace_on_secondary

      run replace_on_primary

    …

    * instance instance5

      run replace_on_secondary

      run replace_on_primary

    * Submitted job ID(s) 162, 163, 164, 165, 166

      waiting for job 162 for instance1

      …

  - Changing the secondary node

    * instance instance1

      run replace_new_secondary node3

    * instance instance2

      run replace_new_secondary node1

    …

    * instance instance5

      run replace_new_secondary node1

    * Submitted job ID(s) 167, 168, 169, 170, 171

      waiting for job 167 for instance1

      …

  - Growing disks

    * instance instance1

      increase disk/0 by 128 MB

    …

    * instance instance5

      increase disk/0 by 128 MB

    * Submitted job ID(s) 173, 174, 175, 176, 177

      waiting for job 173 for instance1

      …

  - Failing over instances

    * instance instance1

    …

    * instance instance5

    * Submitted job ID(s) 179, 180, 181, 182, 183

      waiting for job 179 for instance1

      …

  - Migrating instances

    * instance instance1

      migration and migration cleanup

    …

    * instance instance5

      migration and migration cleanup

    * Submitted job ID(s) 184, 185, 186, 187, 188

      waiting for job 184 for instance1

      …

  - Exporting and re-importing instances

    * instance instance1

      export to node node3

      remove instance

      import from node3 to node1, node2

      remove export

    …

    * instance instance5

      export to node node1

      remove instance

      import from node1 to node2, node3

      remove export

    * Submitted job ID(s) 196, 197, 198, 199, 200

      waiting for job 196 for instance1

      …

  - Reinstalling instances

    * instance instance1

      reinstall without passing the OS

      reinstall specifying the OS

    …

    * instance instance5

      reinstall without passing the OS

      reinstall specifying the OS

    * Submitted job ID(s) 203, 204, 205, 206, 207

      waiting for job 203 for instance1

      …

  - Rebooting instances

    * instance instance1

      reboot with type 'hard'

      reboot with type 'soft'

      reboot with type 'full'

    …

    * instance instance5

      reboot with type 'hard'

      reboot with type 'soft'

      reboot with type 'full'

    * Submitted job ID(s) 208, 209, 210, 211, 212

      waiting for job 208 for instance1

    …

  - Adding and removing disks

    * instance instance1

      adding a disk

      removing last disk

    …

    * instance instance5

      adding a disk

      removing last disk

    * Submitted job ID(s) 213, 214, 215, 216, 217

      waiting for job 213 for instance1

      …

  - Adding and removing NICs

    * instance instance1

      adding a NIC

      removing last NIC

    …

    * instance instance5

      adding a NIC

      removing last NIC

    * Submitted job ID(s) 218, 219, 220, 221, 222

      waiting for job 218 for instance1

      …

  - Activating/deactivating disks

    * instance instance1

      activate disks when online

      activate disks when offline

      deactivate disks (when offline)

    …

    * instance instance5

      activate disks when online

      activate disks when offline

      deactivate disks (when offline)

    * Submitted job ID(s) 223, 224, 225, 226, 227

      waiting for job 223 for instance1

      …

  - Stopping and starting instances

    * instance instance1

    …

    * instance instance5

    * Submitted job ID(s) 230, 231, 232, 233, 234

      waiting for job 230 for instance1

      …

  - Removing instances

    * instance instance1

    …

    * instance instance5

    * Submitted job ID(s) 235, 236, 237, 238, 239

      waiting for job 235 for instance1

      …

  $

You can see in the above what operations the burn-in does. Ideally, the

burn-in log would proceed successfully through all the steps and end

cleanly, without throwing errors.

Instance operations

-------------------

Creation

++++++++

At this point, Ganeti and the hardware seems to be functioning

correctly, so we'll follow up with creating the instances manually::

  $ gnt-instance add -t drbd -o debootstrap -s %256m% %instance3%

  Mon Oct 26 04:06:52 2009  - INFO: Selected nodes for instance instance1 via iallocator hail: node2, node3

  Mon Oct 26 04:06:53 2009 * creating instance disks...

  Mon Oct 26 04:06:57 2009 adding instance instance1 to cluster config

  Mon Oct 26 04:06:57 2009  - INFO: Waiting for instance instance1 to sync disks.

  Mon Oct 26 04:06:57 2009  - INFO: - device disk/0: 20.00\% done, 4 estimated seconds remaining

  Mon Oct 26 04:07:01 2009  - INFO: Instance instance1's disks are in sync.

  Mon Oct 26 04:07:01 2009 creating os for instance instance1 on node node2

  Mon Oct 26 04:07:01 2009 * running the instance OS create scripts...

  Mon Oct 26 04:07:14 2009 * starting instance...

  $ gnt-instance add -t drbd -o debootstrap -s %256m% -n %node1%:%node2% %instance2%

  Mon Oct 26 04:11:37 2009 * creating instance disks...

  Mon Oct 26 04:11:40 2009 adding instance instance2 to cluster config

  Mon Oct 26 04:11:41 2009  - INFO: Waiting for instance instance2 to sync disks.

  Mon Oct 26 04:11:41 2009  - INFO: - device disk/0: 35.40\% done, 1 estimated seconds remaining

  Mon Oct 26 04:11:42 2009  - INFO: - device disk/0: 58.50\% done, 1 estimated seconds remaining

  Mon Oct 26 04:11:43 2009  - INFO: - device disk/0: 86.20\% done, 0 estimated seconds remaining

  Mon Oct 26 04:11:44 2009  - INFO: - device disk/0: 92.40\% done, 0 estimated seconds remaining

  Mon Oct 26 04:11:44 2009  - INFO: - device disk/0: 97.00\% done, 0 estimated seconds remaining

  Mon Oct 26 04:11:44 2009  - INFO: Instance instance2's disks are in sync.

  Mon Oct 26 04:11:44 2009 creating os for instance instance2 on node node1

  Mon Oct 26 04:11:44 2009 * running the instance OS create scripts...

  Mon Oct 26 04:11:57 2009 * starting instance...

  $

The above shows one instance created via an iallocator script, and one

being created with manual node assignment. The other three instances

were also created and now it's time to check them::

  $ gnt-instance list

  Instance  Hypervisor OS          Primary_node Status  Memory

  instance1 xen-pvm    debootstrap node2        running   128M

  instance2 xen-pvm    debootstrap node1        running   128M

  instance3 xen-pvm    debootstrap node1        running   128M

  instance4 xen-pvm    debootstrap node3        running   128M

  instance5 xen-pvm    debootstrap node2        running   128M

Accessing instances

+++++++++++++++++++

Accessing an instance's console is easy::

  $ gnt-instance console %instance2%

  [    0.000000] Bootdata ok (command line is root=/dev/sda1 ro)

  [    0.000000] Linux version 2.6…

  [    0.000000] BIOS-provided physical RAM map:

  [    0.000000]  Xen: 0000000000000000 - 0000000008800000 (usable)

  [13138176.018071] Built 1 zonelists.  Total pages: 34816

  [13138176.018074] Kernel command line: root=/dev/sda1 ro

  [13138176.018694] Initializing CPU#0

  …

  Checking file systems...fsck 1.41.3 (12-Oct-2008)

  done.

  Setting kernel variables (/etc/sysctl.conf)...done.

  Mounting local filesystems...done.

  Activating swapfile swap...done.

  Setting up networking....

  Configuring network interfaces...done.

  Setting console screen modes and fonts.

  INIT: Entering runlevel: 2

  Starting enhanced syslogd: rsyslogd.

  Starting periodic command scheduler: crond.

  Debian GNU/Linux 5.0 instance2 tty1

  instance2 login:

At this moment you can login to the instance and, after configuring the

network (and doing this on all instances), we can check their

connectivity::

  $ fping %instance{1..5}%

  instance1 is alive

  instance2 is alive

  instance3 is alive

  instance4 is alive

  instance5 is alive

  $

Removal

+++++++

Removing unwanted instances is also easy::

  $ gnt-instance remove %instance5%

  This will remove the volumes of the instance instance5 (including

  mirrors), thus removing all the data of the instance. Continue?

  y/[n]/?: %y%

  $

Recovering from hardware failures

---------------------------------

Recovering from node failure

++++++++++++++++++++++++++++

We are now left with four instances. Assume that at this point, node3,

which has one primary and one secondary instance, crashes::

  $ gnt-node info %node3%

  Node name: node3

    primary ip: 198.51.100.1

    secondary ip: 192.0.2.3

    master candidate: True

    drained: False

    offline: False

    primary for instances:

      - instance4

    secondary for instances:

      - instance1

  $ fping %node3%

  node3 is unreachable

At this point, the primary instance of that node (instance4) is down,

but the secondary instance (instance1) is not affected except it has

lost disk redundancy::

  $ fping %instance{1,4}%

  instance1 is alive

  instance4 is unreachable

  $

If we try to check the status of instance4 via the instance info

command, it fails because it tries to contact node3 which is down::

  $ gnt-instance info %instance4%

  Failure: command execution error:

  Error checking node node3: Connection failed (113: No route to host)

  $

So we need to mark node3 as being *offline*, and thus Ganeti won't talk

to it anymore::

  $ gnt-node modify -O yes -f %node3%

  Mon Oct 26 04:34:12 2009  - WARNING: Not enough master candidates (desired 10, new value will be 2)

  Mon Oct 26 04:34:15 2009  - WARNING: Communication failure to node node3: Connection failed (113: No route to host)

  Modified node node3

   - offline -> True

   - master_candidate -> auto-demotion due to offline

  $

And now we can failover the instance::

  $ gnt-instance failover %instance4%

  Failover will happen to image instance4. This requires a shutdown of

  the instance. Continue?

  y/[n]/?: %y%

  Mon Oct 26 04:35:34 2009 * checking disk consistency between source and target

  Failure: command execution error:

  Disk disk/0 is degraded on target node, aborting failover.

  $ gnt-instance failover --ignore-consistency %instance4%

  Failover will happen to image instance4. This requires a shutdown of

  the instance. Continue?

  y/[n]/?: y

  Mon Oct 26 04:35:47 2009 * checking disk consistency between source and target

  Mon Oct 26 04:35:47 2009 * shutting down instance on source node

  Mon Oct 26 04:35:47 2009  - WARNING: Could not shutdown instance instance4 on node node3. Proceeding anyway. Please make sure node node3 is down. Error details: Node is marked offline

  Mon Oct 26 04:35:47 2009 * deactivating the instance's disks on source node

  Mon Oct 26 04:35:47 2009  - WARNING: Could not shutdown block device disk/0 on node node3: Node is marked offline

  Mon Oct 26 04:35:47 2009 * activating the instance's disks on target node

  Mon Oct 26 04:35:47 2009  - WARNING: Could not prepare block device disk/0 on node node3 (is_primary=False, pass=1): Node is marked offline

  Mon Oct 26 04:35:48 2009 * starting the instance on the target node

  $

Note in our first attempt, Ganeti refused to do the failover since it

wasn't sure what is the status of the instance's disks. We pass the

``--ignore-consistency`` flag and then we can failover::

  $ gnt-instance list

  Instance  Hypervisor OS          Primary_node Status  Memory

  instance1 xen-pvm    debootstrap node2        running   128M

  instance2 xen-pvm    debootstrap node1        running   128M

  instance3 xen-pvm    debootstrap node1        running   128M

  instance4 xen-pvm    debootstrap node1        running   128M

  $

But at this point, both instance1 and instance4 are without disk

redundancy::

  $ gnt-instance info %instance1%

  Instance name: instance1

  UUID: 45173e82-d1fa-417c-8758-7d582ab7eef4

  Serial number: 2

  Creation time: 2009-10-26 04:06:57

  Modification time: 2009-10-26 04:07:14

  State: configured to be up, actual state is up

    Nodes:

      - primary: node2

      - secondaries: node3

    Operating system: debootstrap

    Allocated network port: None

    Hypervisor: xen-pvm

      - root_path: default (/dev/sda1)

      - kernel_args: default (ro)

      - use_bootloader: default (False)

      - bootloader_args: default ()

      - bootloader_path: default ()

      - kernel_path: default (/boot/vmlinuz-2.6-xenU)

      - initrd_path: default ()

    Hardware:

      - VCPUs: 1

      - maxmem: 256MiB

      - minmem: 512MiB

      - NICs:

        - nic/0: MAC: aa:00:00:78:da:63, IP: None, mode: bridged, link: xen-br0

    Disks:

      - disk/0: drbd8, size 256M

        access mode: rw

        nodeA:       node2, minor=0

        nodeB:       node3, minor=0

        port:        11035

        auth key:    8e950e3cec6854b0181fbc3a6058657701f2d458

        on primary:  /dev/drbd0 (147:0) in sync, status *DEGRADED*

        child devices:

          - child 0: lvm, size 256M

            logical_id: xenvg/22459cf8-117d-4bea-a1aa-791667d07800.disk0_data

            on primary: /dev/xenvg/22459cf8-117d-4bea-a1aa-791667d07800.disk0_data (254:0)

          - child 1: lvm, size 128M

            logical_id: xenvg/22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta

            on primary: /dev/xenvg/22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta (254:1)

The output is similar for instance4. In order to recover this, we need

to run the node evacuate command which will change from the current

secondary node to a new one (in this case, we only have two working

nodes, so all instances will be end on nodes one and two)::

  $ gnt-node evacuate -I hail %node3%

  Relocate instance(s) 'instance1','instance4' from node

   node3 using iallocator hail?

  y/[n]/?: %y%

  Mon Oct 26 05:05:39 2009  - INFO: Selected new secondary for instance 'instance1': node1

  Mon Oct 26 05:05:40 2009  - INFO: Selected new secondary for instance 'instance4': node2

  Mon Oct 26 05:05:40 2009 Replacing disk(s) 0 for instance1

  Mon Oct 26 05:05:40 2009 STEP 1/6 Check device existence

  Mon Oct 26 05:05:40 2009  - INFO: Checking disk/0 on node2

  Mon Oct 26 05:05:40 2009  - INFO: Checking volume groups

  Mon Oct 26 05:05:40 2009 STEP 2/6 Check peer consistency

  Mon Oct 26 05:05:40 2009  - INFO: Checking disk/0 consistency on node node2

  Mon Oct 26 05:05:40 2009 STEP 3/6 Allocate new storage

  Mon Oct 26 05:05:40 2009  - INFO: Adding new local storage on node1 for disk/0

  Mon Oct 26 05:05:41 2009 STEP 4/6 Changing drbd configuration

  Mon Oct 26 05:05:41 2009  - INFO: activating a new drbd on node1 for disk/0

  Mon Oct 26 05:05:42 2009  - INFO: Shutting down drbd for disk/0 on old node

  Mon Oct 26 05:05:42 2009  - WARNING: Failed to shutdown drbd for disk/0 on oldnode: Node is marked offline

  Mon Oct 26 05:05:42 2009       Hint: Please cleanup this device manually as soon as possible

  Mon Oct 26 05:05:42 2009  - INFO: Detaching primary drbds from the network (=> standalone)

  Mon Oct 26 05:05:42 2009  - INFO: Updating instance configuration

  Mon Oct 26 05:05:45 2009  - INFO: Attaching primary drbds to new secondary (standalone => connected)

  Mon Oct 26 05:05:46 2009 STEP 5/6 Sync devices

  Mon Oct 26 05:05:46 2009  - INFO: Waiting for instance instance1 to sync disks.

  Mon Oct 26 05:05:46 2009  - INFO: - device disk/0: 13.90\% done, 7 estimated seconds remaining

  Mon Oct 26 05:05:53 2009  - INFO: Instance instance1's disks are in sync.

  Mon Oct 26 05:05:53 2009 STEP 6/6 Removing old storage

  Mon Oct 26 05:05:53 2009  - INFO: Remove logical volumes for 0

  Mon Oct 26 05:05:53 2009  - WARNING: Can't remove old LV: Node is marked offline

  Mon Oct 26 05:05:53 2009       Hint: remove unused LVs manually

  Mon Oct 26 05:05:53 2009  - WARNING: Can't remove old LV: Node is marked offline

  Mon Oct 26 05:05:53 2009       Hint: remove unused LVs manually

  Mon Oct 26 05:05:53 2009 Replacing disk(s) 0 for instance4

  Mon Oct 26 05:05:53 2009 STEP 1/6 Check device existence

  Mon Oct 26 05:05:53 2009  - INFO: Checking disk/0 on node1

  Mon Oct 26 05:05:53 2009  - INFO: Checking volume groups

  Mon Oct 26 05:05:53 2009 STEP 2/6 Check peer consistency

  Mon Oct 26 05:05:53 2009  - INFO: Checking disk/0 consistency on node node1

  Mon Oct 26 05:05:54 2009 STEP 3/6 Allocate new storage

  Mon Oct 26 05:05:54 2009  - INFO: Adding new local storage on node2 for disk/0

  Mon Oct 26 05:05:54 2009 STEP 4/6 Changing drbd configuration

  Mon Oct 26 05:05:54 2009  - INFO: activating a new drbd on node2 for disk/0

  Mon Oct 26 05:05:55 2009  - INFO: Shutting down drbd for disk/0 on old node

  Mon Oct 26 05:05:55 2009  - WARNING: Failed to shutdown drbd for disk/0 on oldnode: Node is marked offline

  Mon Oct 26 05:05:55 2009       Hint: Please cleanup this device manually as soon as possible

  Mon Oct 26 05:05:55 2009  - INFO: Detaching primary drbds from the network (=> standalone)

  Mon Oct 26 05:05:55 2009  - INFO: Updating instance configuration

  Mon Oct 26 05:05:55 2009  - INFO: Attaching primary drbds to new secondary (standalone => connected)

  Mon Oct 26 05:05:56 2009 STEP 5/6 Sync devices

  Mon Oct 26 05:05:56 2009  - INFO: Waiting for instance instance4 to sync disks.

  Mon Oct 26 05:05:56 2009  - INFO: - device disk/0: 12.40\% done, 8 estimated seconds remaining

  Mon Oct 26 05:06:04 2009  - INFO: Instance instance4's disks are in sync.

  Mon Oct 26 05:06:04 2009 STEP 6/6 Removing old storage

  Mon Oct 26 05:06:04 2009  - INFO: Remove logical volumes for 0

  Mon Oct 26 05:06:04 2009  - WARNING: Can't remove old LV: Node is marked offline

  Mon Oct 26 05:06:04 2009       Hint: remove unused LVs manually

  Mon Oct 26 05:06:04 2009  - WARNING: Can't remove old LV: Node is marked offline

  Mon Oct 26 05:06:04 2009       Hint: remove unused LVs manually

  $

And now node3 is completely free of instances and can be repaired::

  $ gnt-node list

  Node  DTotal DFree MTotal MNode MFree Pinst Sinst

  node1   1.3T  1.3T  32.0G  1.0G 30.2G     3     1

  node2   1.3T  1.3T  32.0G  1.0G 30.4G     1     3

  node3      ?     ?      ?     ?     ?     0     0

Re-adding a node to the cluster

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Let's say node3 has been repaired and is now ready to be

reused. Re-adding it is simple::

  $ gnt-node add --readd %node3%

  The authenticity of host 'node3 (198.51.100.1)' can't be established.

  RSA key fingerprint is 9f:2e:5a:2e:e0:bd:00:09:e4:5c:32:f2:27:57:7a:f4.

  Are you sure you want to continue connecting (yes/no)? yes

  Mon Oct 26 05:27:39 2009  - INFO: Readding a node, the offline/drained flags were reset

  Mon Oct 26 05:27:39 2009  - INFO: Node will be a master candidate

And it is now working again::

  $ gnt-node list

  Node  DTotal DFree MTotal MNode MFree Pinst Sinst

  node1   1.3T  1.3T  32.0G  1.0G 30.2G     3     1

  node2   1.3T  1.3T  32.0G  1.0G 30.4G     1     3

  node3   1.3T  1.3T  32.0G  1.0G 30.4G     0     0

.. note:: If Ganeti has been built with the htools

   component enabled, you can shuffle the instances around to have a

   better use of the nodes.

Disk failures

+++++++++++++

A disk failure is simpler than a full node failure. First, a single disk

failure should not cause data-loss for any redundant instance; only the

performance of some instances might be reduced due to more network

traffic.

Let take the cluster status in the above listing, and check what volumes

are in use::

  $ gnt-node volumes -o phys,instance %node2%

  PhysDev   Instance

  /dev/sdb1 instance4

  /dev/sdb1 instance4

  /dev/sdb1 instance1

  /dev/sdb1 instance1

  /dev/sdb1 instance3

  /dev/sdb1 instance3

  /dev/sdb1 instance2

  /dev/sdb1 instance2

  $

You can see that all instances on node2 have logical volumes on

``/dev/sdb1``. Let's simulate a disk failure on that disk::

  $ ssh node2

  # on node2

  $ echo offline > /sys/block/sdb/device/state

  $ vgs

    /dev/sdb1: read failed after 0 of 4096 at 0: Input/output error

    /dev/sdb1: read failed after 0 of 4096 at 750153695232: Input/output error

    /dev/sdb1: read failed after 0 of 4096 at 0: Input/output error

    Couldn't find device with uuid '954bJA-mNL0-7ydj-sdpW-nc2C-ZrCi-zFp91c'.

    Couldn't find all physical volumes for volume group xenvg.

    /dev/sdb1: read failed after 0 of 4096 at 0: Input/output error

    /dev/sdb1: read failed after 0 of 4096 at 0: Input/output error

    Couldn't find device with uuid '954bJA-mNL0-7ydj-sdpW-nc2C-ZrCi-zFp91c'.

    Couldn't find all physical volumes for volume group xenvg.

    Volume group xenvg not found

  $

At this point, the node is broken and if we are to examine

instance2 we get (simplified output shown)::

  $ gnt-instance info %instance2%

  Instance name: instance2

  State: configured to be up, actual state is up

    Nodes:

      - primary: node1

      - secondaries: node2

    Disks:

      - disk/0: drbd8, size 256M

        on primary:   /dev/drbd0 (147:0) in sync, status ok

        on secondary: /dev/drbd1 (147:1) in sync, status *DEGRADED* *MISSING DISK*

This instance has a secondary only on node2. Let's verify a primary

instance of node2::

  $ gnt-instance info %instance1%

  Instance name: instance1

  State: configured to be up, actual state is up

    Nodes:

      - primary: node2

      - secondaries: node1

    Disks:

      - disk/0: drbd8, size 256M

        on primary:   /dev/drbd0 (147:0) in sync, status *DEGRADED* *MISSING DISK*

        on secondary: /dev/drbd3 (147:3) in sync, status ok

  $ gnt-instance console %instance1%

  Debian GNU/Linux 5.0 instance1 tty1

  instance1 login: root

  Last login: Tue Oct 27 01:24:09 UTC 2009 on tty1

  instance1:~# date > test

  instance1:~# sync

  instance1:~# cat test

  Tue Oct 27 01:25:20 UTC 2009

  instance1:~# dmesg|tail

  [5439785.235448] NET: Registered protocol family 15

  [5439785.235489] 802.1Q VLAN Support v1.8 Ben Greear <greearb@candelatech.com>

  [5439785.235495] All bugs added by David S. Miller <davem@redhat.com>

  [5439785.235517] XENBUS: Device with no driver: device/console/0

  [5439785.236576] kjournald starting.  Commit interval 5 seconds

  [5439785.236588] EXT3-fs: mounted filesystem with ordered data mode.

  [5439785.236625] VFS: Mounted root (ext3 filesystem) readonly.

  [5439785.236663] Freeing unused kernel memory: 172k freed

  [5439787.533779] EXT3 FS on sda1, internal journal

  [5440655.065431] eth0: no IPv6 routers present

  instance1:~#

As you can see, the instance is running fine and doesn't see any disk

issues. It is now time to fix node2 and re-establish redundancy for the

involved instances.

.. note:: For Ganeti 2.0 we need to fix manually the volume group on

   node2 by running ``vgreduce --removemissing xenvg``

::

  $ gnt-node repair-storage %node2% lvm-vg %xenvg%

  Mon Oct 26 18:14:03 2009 Repairing storage unit 'xenvg' on node2 ...

  $ ssh %node2% vgs

  VG    #PV #LV #SN Attr   VSize   VFree

  xenvg   1   8   0 wz--n- 673.84G 673.84G

  $

This has removed the 'bad' disk from the volume group, which is now left

with only one PV. We can now replace the disks for the involved

instances::

  $ for i in %instance{1..4}%; do gnt-instance replace-disks -a $i; done

  Mon Oct 26 18:15:38 2009 Replacing disk(s) 0 for instance1

  Mon Oct 26 18:15:38 2009 STEP 1/6 Check device existence

  Mon Oct 26 18:15:38 2009  - INFO: Checking disk/0 on node1

  Mon Oct 26 18:15:38 2009  - INFO: Checking disk/0 on node2

  Mon Oct 26 18:15:38 2009  - INFO: Checking volume groups

  Mon Oct 26 18:15:38 2009 STEP 2/6 Check peer consistency

  Mon Oct 26 18:15:38 2009  - INFO: Checking disk/0 consistency on node node1

  Mon Oct 26 18:15:39 2009 STEP 3/6 Allocate new storage

  Mon Oct 26 18:15:39 2009  - INFO: Adding storage on node2 for disk/0

  Mon Oct 26 18:15:39 2009 STEP 4/6 Changing drbd configuration

  Mon Oct 26 18:15:39 2009  - INFO: Detaching disk/0 drbd from local storage

  Mon Oct 26 18:15:40 2009  - INFO: Renaming the old LVs on the target node

  Mon Oct 26 18:15:40 2009  - INFO: Renaming the new LVs on the target node

  Mon Oct 26 18:15:40 2009  - INFO: Adding new mirror component on node2

  Mon Oct 26 18:15:41 2009 STEP 5/6 Sync devices

  Mon Oct 26 18:15:41 2009  - INFO: Waiting for instance instance1 to sync disks.

  Mon Oct 26 18:15:41 2009  - INFO: - device disk/0: 12.40\% done, 9 estimated seconds remaining

  Mon Oct 26 18:15:50 2009  - INFO: Instance instance1's disks are in sync.

  Mon Oct 26 18:15:50 2009 STEP 6/6 Removing old storage

  Mon Oct 26 18:15:50 2009  - INFO: Remove logical volumes for disk/0

  Mon Oct 26 18:15:52 2009 Replacing disk(s) 0 for instance2

  Mon Oct 26 18:15:52 2009 STEP 1/6 Check device existence

  …

  Mon Oct 26 18:16:01 2009 STEP 6/6 Removing old storage

  Mon Oct 26 18:16:01 2009  - INFO: Remove logical volumes for disk/0

  Mon Oct 26 18:16:02 2009 Replacing disk(s) 0 for instance3

  Mon Oct 26 18:16:02 2009 STEP 1/6 Check device existence

  …

  Mon Oct 26 18:16:09 2009 STEP 6/6 Removing old storage

  Mon Oct 26 18:16:09 2009  - INFO: Remove logical volumes for disk/0

  Mon Oct 26 18:16:10 2009 Replacing disk(s) 0 for instance4

  Mon Oct 26 18:16:10 2009 STEP 1/6 Check device existence

  …

  Mon Oct 26 18:16:18 2009 STEP 6/6 Removing old storage

  Mon Oct 26 18:16:18 2009  - INFO: Remove logical volumes for disk/0

  $

As this point, all instances should be healthy again.

.. note:: Ganeti 2.0 doesn't have the ``-a`` option to replace-disks, so

   for it you have to run the loop twice, once over primary instances

   with argument ``-p`` and once secondary instances with argument

   ``-s``, but otherwise the operations are similar::

     $ gnt-instance replace-disks -p instance1

     …

     $ for i in %instance{2..4}%; do gnt-instance replace-disks -s $i; done

Common cluster problems

-----------------------

There are a number of small issues that might appear on a cluster that

can be solved easily as long as the issue is properly identified. For

this exercise we will consider the case of node3, which was broken

previously and re-added to the cluster without reinstallation. Running

cluster verify on the cluster reports::

  $ gnt-cluster verify

  Mon Oct 26 18:30:08 2009 * Verifying global settings

  Mon Oct 26 18:30:08 2009 * Gathering data (3 nodes)

  Mon Oct 26 18:30:10 2009 * Verifying node status

  Mon Oct 26 18:30:10 2009   - ERROR: node node3: unallocated drbd minor 0 is in use

  Mon Oct 26 18:30:10 2009   - ERROR: node node3: unallocated drbd minor 1 is in use

  Mon Oct 26 18:30:10 2009 * Verifying instance status

  Mon Oct 26 18:30:10 2009   - ERROR: instance instance4: instance should not run on node node3

  Mon Oct 26 18:30:10 2009 * Verifying orphan volumes

  Mon Oct 26 18:30:10 2009   - ERROR: node node3: volume 22459cf8-117d-4bea-a1aa-791667d07800.disk0_data is unknown

  Mon Oct 26 18:30:10 2009   - ERROR: node node3: volume 1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_data is unknown

  Mon Oct 26 18:30:10 2009   - ERROR: node node3: volume 1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_meta is unknown

  Mon Oct 26 18:30:10 2009   - ERROR: node node3: volume 22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta is unknown

  Mon Oct 26 18:30:10 2009 * Verifying remaining instances

  Mon Oct 26 18:30:10 2009 * Verifying N+1 Memory redundancy

  Mon Oct 26 18:30:10 2009 * Other Notes

  Mon Oct 26 18:30:10 2009 * Hooks Results

  $

Instance status

+++++++++++++++

As you can see, *instance4* has a copy running on node3, because we

forced the failover when node3 failed. This case is dangerous as the

instance will have the same IP and MAC address, wreaking havoc on the

network environment and anyone who tries to use it.

Ganeti doesn't directly handle this case. It is recommended to logon to

node3 and run::

  $ xm destroy %instance4%

Unallocated DRBD minors

+++++++++++++++++++++++

There are still unallocated DRBD minors on node3. Again, these are not

handled by Ganeti directly and need to be cleaned up via DRBD commands::

  $ ssh %node3%

  # on node 3

  $ drbdsetup /dev/drbd%0% down

  $ drbdsetup /dev/drbd%1% down

  $

Orphan volumes

++++++++++++++

At this point, the only remaining problem should be the so-called

*orphan* volumes. This can happen also in the case of an aborted

disk-replace, or similar situation where Ganeti was not able to recover

automatically. Here you need to remove them manually via LVM commands::

  $ ssh %node3%

  # on node3

  $ lvremove %xenvg%

  Do you really want to remove active logical volume "22459cf8-117d-4bea-a1aa-791667d07800.disk0_data"? [y/n]: %y%

    Logical volume "22459cf8-117d-4bea-a1aa-791667d07800.disk0_data" successfully removed

  Do you really want to remove active logical volume "22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta"? [y/n]: %y%

    Logical volume "22459cf8-117d-4bea-a1aa-791667d07800.disk0_meta" successfully removed

  Do you really want to remove active logical volume "1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_data"? [y/n]: %y%

    Logical volume "1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_data" successfully removed

  Do you really want to remove active logical volume "1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_meta"? [y/n]: %y%

    Logical volume "1aaf4716-e57f-4101-a8d6-03af5da9dc50.disk0_meta" successfully removed

  node3#

At this point cluster verify shouldn't complain anymore::

  $ gnt-cluster verify

  Mon Oct 26 18:37:51 2009 * Verifying global settings

  Mon Oct 26 18:37:51 2009 * Gathering data (3 nodes)

  Mon Oct 26 18:37:53 2009 * Verifying node status

  Mon Oct 26 18:37:53 2009 * Verifying instance status

  Mon Oct 26 18:37:53 2009 * Verifying orphan volumes

  Mon Oct 26 18:37:53 2009 * Verifying remaining instances

  Mon Oct 26 18:37:53 2009 * Verifying N+1 Memory redundancy

  Mon Oct 26 18:37:53 2009 * Other Notes

  Mon Oct 26 18:37:53 2009 * Hooks Results

  $

N+1 errors

++++++++++

Since redundant instances in Ganeti have a primary/secondary model, it

is needed to leave aside on each node enough memory so that if one of

its peer node fails, all the secondary instances that have that node as

primary can be relocated. More specifically, if instance2 has node1 as

primary and node2 as secondary (and node1 and node2 do not have any

other instances in this layout), then it means that node2 must have

enough free memory so that if node1 fails, we can failover instance2

without any other operations (for reducing the downtime window). Let's

increase the memory of the current instances to 4G, and add three new

instances, two on node2:node3 with 8GB of RAM and one on node1:node2,

with 12GB of RAM (numbers chosen so that we run out of memory)::

  $ gnt-instance modify -B memory=%4G% %instance1%

  Modified instance instance1

   - be/maxmem -> 4096

   - be/minmem -> 4096

  Please don't forget that these parameters take effect only at the next start of the instance.

  $ gnt-instance modify …

  $ gnt-instance add -t drbd -n %node2%:%node3% -s %512m% -B memory=%8G% -o %debootstrap% %instance5%

  …

  $ gnt-instance add -t drbd -n %node2%:%node3% -s %512m% -B memory=%8G% -o %debootstrap% %instance6%

  …

  $ gnt-instance add -t drbd -n %node1%:%node2% -s %512m% -B memory=%8G% -o %debootstrap% %instance7%

  $ gnt-instance reboot --all

  The reboot will operate on 7 instances.

  Do you want to continue?

  Affected instances:

    instance1

    instance2

    instance3

    instance4

    instance5

    instance6

    instance7

  y/[n]/?: %y%

  Submitted jobs 677, 678, 679, 680, 681, 682, 683

  Waiting for job 677 for instance1...

  Waiting for job 678 for instance2...

  Waiting for job 679 for instance3...

  Waiting for job 680 for instance4...

  Waiting for job 681 for instance5...

  Waiting for job 682 for instance6...

  Waiting for job 683 for instance7...

  $

We rebooted the instances for the memory changes to have effect. Now the

cluster looks like::

  $ gnt-node list

  Node  DTotal DFree MTotal MNode MFree Pinst Sinst

  node1   1.3T  1.3T  32.0G  1.0G  6.5G     4     1

  node2   1.3T  1.3T  32.0G  1.0G 10.5G     3     4

  node3   1.3T  1.3T  32.0G  1.0G 30.5G     0     2

  $ gnt-cluster verify

  Mon Oct 26 18:59:36 2009 * Verifying global settings

  Mon Oct 26 18:59:36 2009 * Gathering data (3 nodes)

  Mon Oct 26 18:59:37 2009 * Verifying node status

  Mon Oct 26 18:59:37 2009 * Verifying instance status

  Mon Oct 26 18:59:37 2009 * Verifying orphan volumes

  Mon Oct 26 18:59:37 2009 * Verifying remaining instances

  Mon Oct 26 18:59:37 2009 * Verifying N+1 Memory redundancy

  Mon Oct 26 18:59:37 2009   - ERROR: node node2: not enough memory to accommodate instance failovers should node node1 fail

  Mon Oct 26 18:59:37 2009 * Other Notes

  Mon Oct 26 18:59:37 2009 * Hooks Results

  $

The cluster verify error above shows that if node1 fails, node2 will not

have enough memory to failover all primary instances on node1 to it. To

solve this, you have a number of options:

- try to manually move instances around (but this can become complicated

  for any non-trivial cluster)

- try to reduce the minimum memory of some instances on the source node

  of the N+1 failure (in the example above ``node1``): this will allow

  it to start and be failed over/migrated with less than its maximum

  memory

- try to reduce the runtime/maximum memory of some instances on the

  destination node of the N+1 failure (in the example above ``node2``)

  to create additional available node memory (check the :doc:`admin`

  guide for what Ganeti will and won't automatically do in regards to

  instance runtime memory modification)

- if Ganeti has been built with the htools package enabled, you can run

  the ``hbal`` tool which will try to compute an automated cluster

  solution that complies with the N+1 rule

Network issues

++++++++++++++

In case a node has problems with the network (usually the secondary

network, as problems with the primary network will render the node

unusable for ganeti commands), it will show up in cluster verify as::

  $ gnt-cluster verify

  Mon Oct 26 19:07:19 2009 * Verifying global settings

  Mon Oct 26 19:07:19 2009 * Gathering data (3 nodes)

  Mon Oct 26 19:07:23 2009 * Verifying node status

  Mon Oct 26 19:07:23 2009   - ERROR: node node1: tcp communication with node 'node3': failure using the secondary interface(s)

  Mon Oct 26 19:07:23 2009   - ERROR: node node2: tcp communication with node 'node3': failure using the secondary interface(s)

  Mon Oct 26 19:07:23 2009   - ERROR: node node3: tcp communication with node 'node1': failure using the secondary interface(s)

  Mon Oct 26 19:07:23 2009   - ERROR: node node3: tcp communication with node 'node2': failure using the secondary interface(s)

  Mon Oct 26 19:07:23 2009   - ERROR: node node3: tcp communication with node 'node3': failure using the secondary interface(s)

  Mon Oct 26 19:07:23 2009 * Verifying instance status

  Mon Oct 26 19:07:23 2009 * Verifying orphan volumes

  Mon Oct 26 19:07:23 2009 * Verifying remaining instances

  Mon Oct 26 19:07:23 2009 * Verifying N+1 Memory redundancy

  Mon Oct 26 19:07:23 2009 * Other Notes

  Mon Oct 26 19:07:23 2009 * Hooks Results

  $

This shows that both node1 and node2 have problems contacting node3 over

the secondary network, and node3 has problems contacting them. From this

output is can be deduced that since node1 and node2 can communicate

between themselves, node3 is the one having problems, and you need to

investigate its network settings/connection.