ganeti.mdwn

[Ganeti](http://ganeti.org/) is software designed to facilitate the management of
virtual machines (KVM or Xen). It helps you move virtual machine
instances from one node to another, create an instance with DRBD
replication on another node and do the live migration from one to
another, etc.

[[!toc levels=3]]

# Tutorial

## Listing virtual machines (instances)

This will show the running guests, known as "instances":

    gnt-instance list

## Accessing serial console

Our instances do serial console, starting in grub.  To access it, run

    gnt-instance console test01.torproject.org

To exit, use `^]` -- that is, Control-<Closing Bracket>.

# How-to

## Glossary

In Ganeti, a physical machine is called a *node* and a virtual machine
is an *instance*. A node is elected to be the *master* where all
commands should be ran from. Nodes are interconnected through a
private network that is used to communicate commands and synchronise
disks (with [[drbd]]). Instances are normally assigned two nodes: a
*primary* and a *secondary*: the *primary* is where the virtual
machine actually runs and th *secondary* acts as a hot failover.

See also the more extensive [glossary in the Ganeti documentation](http://docs.ganeti.org/ganeti/2.15/html/glossary.html).

## Adding a new instance

This command creates a new guest, or "instance" in Ganeti's
vocabulary:

    gnt-instance add \
      -o debootstrap+buster \
      -t drbd --no-wait-for-sync \
      --disk 0:size=10G \
      --disk 1:size=2G,name=swap \
      --disk 2:size=20G \
      --disk 3:size=800G,vg=vg_ganeti_hdd \
      --backend-parameters memory=8g,vcpus=2 \
      --net 0:ip=pool,network=gnt-fsn \
      --no-name-check \
      --no-ip-check \
      static-master-fsn.torproject.org

WARNING: there is a bug in `ganeti-instance-debootstrap` which
misconfigures `ping` (among other things), see [bug #31781](https://bugs.torproject.org/31781). It's
currently patched in our version of the Debian package, but that patch
might disappear if Debian upgrade the package without [shipping our
patch](https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=944538).

This configures the following:

 * redundant disks in a DRBD mirror, use `-t plain` instead of `-t drbd` for
   tests as that avoids syncing of disks and will speed things up considerably
   (even with `--no-wait-for-sync` there are some operations that block on
   synced mirrors).  Only one node should be provided as the argument for
   `--node` then.
 * three partitions: one on the default VG (SSD), one on another (HDD)
   and a swap file on the default VG, if you don't specify a swap device,
   a 512MB swapfile is created in `/swapfile`
 * 2GB of RAM with 2 virtual CPUs
 * an IP allocated from the public gnt-fsn pool:
   `gnt-instance add` will print the IPv4 address it picked to stdout.  The
   IPv6 address can be found in `/var/log/ganeti/os/` on the primary node
   of the instance, see below.
 * with the `test01.torproject.org` hostname

To find the root password, ssh host key fingerprints, and the IPv6
address, run this **on the node where the instance was created**, for
example:

    egrep 'root password|configured eth0 with|SHA256' $(ls -tr /var/log/ganeti/os/* | tail -1) | grep -v $(hostname)

Note that you need to use the `--node` parameter to pick on which
machines you want the machine to end up, otherwise Ganeti will choose
for you. Use, for example, `--node fsn-node-01:fsn-node-02` to use
`node-01` as primary and `node-02` as secondary. It might be better to
let the Ganeti allocator do its job since it will, eventually do this
during cluster rebalancing.

We copy root's authorized keys into the new instance, so you should be able to
log in with your token.  You will be required to change the root password immediately.
Pick something nice and document it in `tor-passwords`.

Also set reverse DNS for both IPv4 and IPv6 in [hetzner's robot](https://robot.your-server.de/).
(Chek under servers -> vSwitch -> IPs)

Then follow [[new-machine]].

## Modifying an instance

It's possible to change the IP, CPU, or memory allocation of an instance
using the [gnt-instance modify](http://docs.ganeti.org/ganeti/2.15/man/gnt-instance.html#modify) command:

    gnt-instance modify -B vcpus=2 test1.torproject.org
    gnt-instance modify -B memory=4g test1.torproject.org
    gnt-instance reboot test1.torproject.org

IP address changes require a full stop and will require manual changes
to the `/etc/network/interfaces*` files:

    gnt-instance modify --net 0:modify,ip=116.202.120.175 test1.torproject.org
    gnt-instance stop test1.torproject.org
    gnt-instance start test1.torproject.org
    gnt-instance console test1.torproject.org

The [gnt-instance grow-disk](http://docs.ganeti.org/ganeti/2.15/man/gnt-instance.html#grow-disk) command can be used to change the size
of the underlying device:

    gnt-instance grow-disk test1.torproject.org 0 16g
    gnt-instance reboot test1.torproject.org

The number `0` in this context, indicates the first disk of the
instance. Then the filesystem needs to be resized inside the VM:

    ssh root@test1.torproject.org resize2fs /dev/sda1

## Destroying an instance

This totally deletes the instance, including all mirrors and
everything, be very careful with it:

    gnt-instance remove test01.torproject.org

## Disk operations (DRBD)

Instances should be setup using the DRBD backend, in which case you
should probably take a look at [[drbd]] if you have problems with
that. Ganeti handles most of the logic there so that should generally
not be necessary.

## Evaluating cluster capacity

This will list instances repeatedly, but also show their assigned
memory, and compare it with the node's capacity:

    watch -n5 -d 'gnt-instance list -o pnode,name,be/vcpus,be/memory,status,disk_template  |  sort; echo; gnt-node list'

The [gnt-cluster verify](http://docs.ganeti.org/ganeti/2.15/man/gnt-cluster.html#verify) command will also check to see if there's
enough space on secondaries to account for the failure of a
node. Healthy output looks like this:

    root@fsn-node-01:~# gnt-cluster verify
    Submitted jobs 48030, 48031
    Waiting for job 48030 ...
    Fri Jan 17 20:05:42 2020 * Verifying cluster config
    Fri Jan 17 20:05:42 2020 * Verifying cluster certificate files
    Fri Jan 17 20:05:42 2020 * Verifying hypervisor parameters
    Fri Jan 17 20:05:42 2020 * Verifying all nodes belong to an existing group
    Waiting for job 48031 ...
    Fri Jan 17 20:05:42 2020 * Verifying group 'default'
    Fri Jan 17 20:05:42 2020 * Gathering data (2 nodes)
    Fri Jan 17 20:05:42 2020 * Gathering information about nodes (2 nodes)
    Fri Jan 17 20:05:45 2020 * Gathering disk information (2 nodes)
    Fri Jan 17 20:05:45 2020 * Verifying configuration file consistency
    Fri Jan 17 20:05:45 2020 * Verifying node status
    Fri Jan 17 20:05:45 2020 * Verifying instance status
    Fri Jan 17 20:05:45 2020 * Verifying orphan volumes
    Fri Jan 17 20:05:45 2020 * Verifying N+1 Memory redundancy
    Fri Jan 17 20:05:45 2020 * Other Notes
    Fri Jan 17 20:05:45 2020 * Hooks Results

A sick node would have said something like this instead:

    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

See the [ganeti manual](http://docs.ganeti.org/ganeti/2.15/html/walkthrough.html#n-1-errors) for a more extensive example

## Moving instances and failover

Ganeti is smart about assigning instances to nodes. There's also a
command (`hbal`) to automatically rebalance the cluster (see
below). If for some reason hbal doesn’t do what you want or you need
to move things around for other reasons, here are a few commands that
might be handy.

Make an instance switch to using it's secondary:

    gnt-instance migrate test1.torproject.org

Make all instances on a node switch to their secondaries:

    gnt-node migrate test1.torproject.org

The `migrate` commands does a "live" migrate which should avoid any
downtime during the migration. It might be preferable to actually
shutdown the machine for some reason (for example if we actually want
to reboot because of a security upgrade). Or we might not be able to
live-migrate because the node is down. In this case, we do a
[failover](http://docs.ganeti.org/ganeti/2.15/html/admin.html#failing-over-an-instance)

    gnt-instance failover test1.torproject.org

The [gnt-node evacuate](http://docs.ganeti.org/ganeti/2.15/man/gnt-node.html#evacuate) command can also be used to "empty" a given
node altogether, in case of an emergency:

    gnt-node evacuate -I . fsn-node-02.torproject.org

Similarly, the [gnt-node failover](http://docs.ganeti.org/ganeti/2.15/man/gnt-node.html#failover) command can be used to
hard-recover from a completely crashed node:

    gnt-node failover fsn-node-02.torproject.org

Note that you might need the `--ignore-consistency` flag if the
node is unresponsive.

## Importing external instances

Assumptions:

 * `INSTANCE`: name of the instance being migrated, the "old" one
   being outside the cluster and the "new" one being the one created
   inside the cluster (e.g. `chiwui.torproject.org`)
 * `SPARE_NODE`: a ganeti node with free space
   (e.g. `fsn-node-03.torproject.org`) where the `INSTANCE` will be
   migrated
 * `MASTER_NODE`: the master ganeti node
   (e.g. `fsn-node-01.torproject.org`)
 * `KVM_HOST`: the machine which we migrate the `INSTANCE` from
 * the `INSTANCE` has only `root` and `swap` partitions

Import procedure:

 1. pick a viable SPARE NODE to import the instance (see "evaluating
    cluster capacity" above, when in doubt), login to the three
    servers, setting the proper environment everywhere, for example:
    
        MASTER_NODE=fsn-node-01.torproject.org
        SPARE_NODE=fsn-node-03.torproject.org
        KVM_HOST=kvm1.torproject.org
        INSTANCE=test.torproject.org

 2. establish VM specs, on the KVM HOST:
 
    * disk space in GiB:
    
          for disk in /srv/vmstore/$INSTANCE/*; do
              printf "$disk: "
              echo "$(qemu-img info --output=json $disk | jq '."virtual-size"') / 1024 / 1024 / 1024" | bc -l
          done

    * number of CPU cores:

          sed -n '/<vcpu/{s/[^>]*>//;s/<.*//;p}' < /etc/libvirt/qemu/$INSTANCE.xml

    * memory, assuming from KiB to GiB:

          echo "$(sed -n '/<memory/{s/[^>]*>//;s/<.*//;p}' < /etc/libvirt/qemu/$INSTANCE.xml) /1024 /1024" | bc -l

      TODO: make sure the memory line is in KiB and that the number
      makes sense.

    * on the INSTANCE, find the swap device UUID so we can recreate it later:

          blkid -t TYPE=swap -s UUID -o value

 3. setup a copy channel, on the SPARE NODE:
 
        ssh-agent bash
        ssh-add /etc/ssh/ssh_host_ed25519_key
        cat /etc/ssh/ssh_host_ed25519_key.pub

    on the KVM HOST:
    
        echo "$KEY_FROM_SPARE_NODE" >> /etc/ssh/userkeys/root

 4. copy the `.qcow` file(s) over, from the KVM HOST to the SPARE NODE:
 
        rsync -P $KVM_HOST:/srv/vmstore/$INSTANCE/$INSTANCE-root /srv/
        rsync -P $KVM_HOST:/srv/vmstore/$INSTANCE/$INSTANCE-lvm /srv/ || true

    Warning: the FSN nodes don't have SSH access everywhere due to a
    flaw in our installation process ([ticket #33143](https://trac.torproject.org/projects/tor/ticket/33143]). You will
    need to manually allow them to connect with iptables before the
    above will work, on the KVM HOST:
    
        iptables -I INPUT -s $SPARE_NODE -j ACCEPT

    Note: it's possible there is not enough room in `/srv`: in the
    base Ganeti installs, everything is in the same root partition
    (`/`) which will fill up if the instance is (say) over ~30GiB. In
    that case, create a filesystem in `/srv`:

        (mkdir /root/srv && mv /srv/* /root/srv true) || true &&
        lvcreate -L 200G vg_ganeti -n srv &&
        mkfs /dev/vg_ganeti/srv &&
        echo "/dev/vg_ganeti/srv /srv ext4 rw,noatime,errors=remount-ro 0 2" >> /etc/fstab &&
        mount /srv &&
        ( mv /root/srv/* ; rmdir /root/srv )

    This partition can be reclaimed once the VM migrations are
    completed, as it needlessly takes up space on the node.

 5. on the SPARE NODE, create and initialize a logical volume with the predetermined size:
 
        lvcreate -L 4GiB -n $INSTANCE-swap vg_ganeti
        mkswap --uuid $SWAP_UUID /dev/vg_ganeti/$INSTANCE-swap
        lvcreate -L 20GiB -n $INSTANCE-root vg_ganeti
        qemu-img convert /srv/$INSTANCE-root  -O raw /dev/vg_ganeti/$INSTANCE-root
        lvcreate -L 40GiB -n $INSTANCE-lvm vg_ganeti_hdd
        qemu-img convert /srv/$INSTANCE-lvm  -O raw /dev/vg_ganeti_hdd/$INSTANCE-lvm

    Note how we assume two disks above, but the instance might have a
    different configuration that would require changing the above. The
    above, common, configuration is to have an LVM disk separate from
    the "root" disk, the former being on a HDD, but the HDD is
    sometimes completely omitted and sizes can differ.
    
    Sometimes it might be worth using pv to get progress on long
    transfers:
    
        qemu-img convert /srv/$INSTANCE-lvm -O raw /srv/$INSTANCE-lvm.raw
        pv /srv/$INSTANCE-lvm.raw | dd of=/dev/vg_ganeti_hdd/$INSTANCE-lvm bs=4k

    TODO: ideally, the above procedure (and many steps below as well)
    would be automatically deduced from the disk listing established
    in the first step.

 6. on the MASTER NODE, create the instance, adopting the LV:
 
        gnt-instance add -t plain \
            -n fsn-node-03 \
            --disk 0:adopt=$INSTANCE-root \
            --disk 1:adopt=$INSTANCE-swap \
            --disk 2:adopt=$INSTANCE-lvm,vg=vg_ganeti_hdd \
            --backend-parameters memory=2g,vcpus=2 \
            --net 0:ip=pool,network=gnt-fsn \
            --no-name-check \
            --no-ip-check \
            -o debootstrap+default \
            $INSTANCE

 7. cross your fingers and watch the party:
 
        gnt-instance console $INSTANCE

 9. IP address change on new instance:
 
      edit `/etc/hosts` and `/etc/network/interfaces` by hand and add
      IPv4 and IPv6 ip. IPv4 configuration can be found in:
      
          gnt-instance show $INSTANCE
          
      Latter can be guessed by concatenating `2a01:4f8:fff0:4f::` and
      the IPv6 local local address without `fe80::`. For example: a
      link local address of `fe80::266:37ff:fe65:870f/64` should yield
      the following configuration:
      
          iface eth0 inet6 static
              accept_ra 0
              address 2a01:4f8:fff0:4f:266:37ff:fe65:870f/64
              gateway 2a01:4f8:fff0:4f::1

      TODO: reuse `gnt-debian-interfaces` from the ganeti puppet
      module script here?

 10. functional tests: change your `/etc/hosts` to point to the new
     server and see if everything still kind of works

 11. shutdown original instance

 12. resync and reconvert image, on the Ganeti MASTER NODE:
 
         gnt-instance stop $INSTANCE

     on the Ganeti node:

         rsync -P $KVM_HOST:/srv/vmstore/$INSTANCE/$INSTANCE-root /srv/ &&
         qemu-img convert /srv/$INSTANCE-root  -O raw /dev/vg_ganeti/$INSTANCE-root &&
         rsync -P $KVM_HOST:/srv/vmstore/$INSTANCE/$INSTANCE-lvm /srv/ &&
         qemu-img convert /srv/$INSTANCE-lvm  -O raw /dev/vg_ganeti_hdd/$INSTANCE-lvm

 13. switch to DRBD, still on the Ganeti MASTER NODE:

         gnt-instance modify -t drbd $INSTANCE
         gnt-instance failover $INSTANCE
         gnt-instance startup $INSTANCE

 14. redo IP adress change in `/etc/network/interfaces` and `/etc/hosts`

 15. final functional test

 16. change IP address in the following locations:

     * nagios (don't forget to change the parent)
     * LDAP (`ipHostNumber` field, but also change the `physicalHost` and `l` fields!)
     * Puppet (grep in tor-puppet source, run `puppet agent -t; ud-replicate` on pauli)
     * DNS (grep in tor-dns source, `puppet agent -t; ud-replicate` on nevii)
     * reverse DNS (upstream web UI, e.g. Hetzner Robot)

 17. decomission old instance ([[retire-a-host]])

### Troubleshooting

 * if boot takes a long time and you see a message like this on the console:
 
        [  *** ] A start job is running for dev-disk-by\x2duuid-484b5...26s / 1min 30s)

   ... which is generally followed by:
   
        [DEPEND] Dependency failed for /dev/disk/by-…6f4b5-f334-4173-8491-9353d4f94e04.
        [DEPEND] Dependency failed for Swap.

   it means the swap device UUID wasn't setup properly, and does not
   match the one provided in `/etc/fstab`. That is probably because
   you missed the `mkswap -U` step documented above.

### References

 * [Upstream docs](http://docs.ganeti.org/ganeti/2.15/html/admin.html#import-of-foreign-instances) have the canonical incantation:

        gnt-instance add -t plain -n HOME_NODE ... --disk 0:adopt=lv_name[,vg=vg_name] INSTANCE_NAME

 * [DSA docs](https://dsa.debian.org/howto/install-ganeti/) also use disk adoption and have a procedure to
   migrate to DRBD

 * [Riseup docs](https://we.riseup.net/riseup+tech/ganeti#move-an-instance-from-one-cluster-to-another-from-) suggest creating a VM without installing, shutting
   down and then syncing

Ganeti [supports importing and exporting](http://docs.ganeti.org/ganeti/2.15/html/design-ovf-support.html?highlight=qcow) from the [Open
Virtualization Format](https://en.wikipedia.org/wiki/Open_Virtualization_Format) (OVF), but unfortunately it [doesn't seem
libvirt supports *exporting* to OVF](https://forums.centos.org/viewtopic.php?t=49231). There's a [virt-convert](http://manpages.debian.org/virt-convert)
tool which can *import* OVF, but not the reverse. The [libguestfs](http://www.libguestfs.org/)
library also has a [converter](http://www.libguestfs.org/virt-v2v.1.html) but it also doesn't support
exporting to OVF or anything Ganeti can load directly.

So people have written [their own conversion tools](https://virtuallyhyper.com/2013/06/migrate-from-libvirt-kvm-to-virtualbox/) or [their own
conversion procedure](https://scienceofficersblog.blogspot.com/2014/04/using-cloud-images-with-ganeti.html).

Ganeti also supports [file-backed instances](http://docs.ganeti.org/ganeti/2.15/html/design-file-based-storage.html) but "adoption" is
specifically designed for logical volumes, so it doesn't work for our
use case.

## Rebooting

Those hosts need special care, as we can accomplish zero-downtime
reboots on those machines. There's a script (`ganeti-reboot-cluster`)
deployed in the ganeti cluster that can be ran on the master to
migrate all instances around and perform a clean reboot.

Such a reboot should be ran interactively, inside a `tmux` or `screen`
session, and takes over 15 minutes to complete right now, but depends
on the size of the cluster (in terms of core memory usage).

Once the reboot is completed, all instances might end up on a single
machine, and the cluster might need to be rebalanced. This is
automatically scheduled by the `ganeti-reboot-cluster` script and will
be done within 30 minutes of the reboot.

## Rebalancing a cluster

After a reboot or a downtime, all nodes might end up on the same
machine. This is normally handled by the reboot script, but it might
be desirable to do this by hand if there was a crash or another
special condition.

This can be easily corrected with this command, which will spread
instances around the cluster to balance it:

    hbal -L -C -v -X

This will automatically move the instances around and rebalance the
cluster. Here's an example run on a small cluster:

    root@fsn-node-01:~# gnt-instance list
    Instance                          Hypervisor OS                 Primary_node               Status  Memory
    loghost01.torproject.org          kvm        debootstrap+buster fsn-node-02.torproject.org running   2.0G
    onionoo-backend-01.torproject.org kvm        debootstrap+buster fsn-node-02.torproject.org running  12.0G
    static-master-fsn.torproject.org  kvm        debootstrap+buster fsn-node-02.torproject.org running   8.0G
    web-fsn-01.torproject.org         kvm        debootstrap+buster fsn-node-02.torproject.org running   4.0G
    web-fsn-02.torproject.org         kvm        debootstrap+buster fsn-node-02.torproject.org running   4.0G
    root@fsn-node-01:~# hbal -L -X
    Loaded 2 nodes, 5 instances
    Group size 2 nodes, 5 instances
    Selected node group: default
    Initial check done: 0 bad nodes, 0 bad instances.
    Initial score: 8.45007519
    Trying to minimize the CV...
        1. onionoo-backend-01 fsn-node-02:fsn-node-01 => fsn-node-01:fsn-node-02   4.98124611 a=f
        2. loghost01          fsn-node-02:fsn-node-01 => fsn-node-01:fsn-node-02   1.78271883 a=f
    Cluster score improved from 8.45007519 to 1.78271883
    Solution length=2
    Got job IDs 16345
    Got job IDs 16346
    root@fsn-node-01:~# gnt-instance list
    Instance                          Hypervisor OS                 Primary_node               Status  Memory
    loghost01.torproject.org          kvm        debootstrap+buster fsn-node-01.torproject.org running   2.0G
    onionoo-backend-01.torproject.org kvm        debootstrap+buster fsn-node-01.torproject.org running  12.0G
    static-master-fsn.torproject.org  kvm        debootstrap+buster fsn-node-02.torproject.org running   8.0G
    web-fsn-01.torproject.org         kvm        debootstrap+buster fsn-node-02.torproject.org running   4.0G
    web-fsn-02.torproject.org         kvm        debootstrap+buster fsn-node-02.torproject.org running   4.0G

In the above example, you should notice that the `web-fsn` instances both
ended up on the same node. That's because the balancer did not know
that they should be distributed. A special configuration was done,
below, to avoid that problem in the future. But as a workaround,
instances can also be moved by hand and the cluster re-balanced.

## Redundant instances distribution

Some instances are redundant across the cluster and should *not* end up
on the same node. A good example are the `web-fsn-01` and `web-fsn-02`
instances which, in theory, would serve similar traffic. If they end
up on the same node, it might flood the network on that machine or at
least defeats the purpose of having redundant machines.

The way to ensure they get distributed properly by the balancing
algorithm is to "tag" them. For the web nodes, for example, this was
performed on the master:

    gnt-instance add-tags web-fsn-01.torproject.org web-fsn
    gnt-instance add-tags web-fsn-02.torproject.org web-fsn
    gnt-cluster add-tags htools:iextags:web-fsn

This tells Ganeti that `web-fsn` is an "exclusion tag" and the
optimizer will not try to schedule instances with those tags on the
same node.

To see which tags are present, use:

    # gnt-cluster list-tags
    htools:iextags:web-fsn

You can also find which nodes are assigned to a tag with:

    # gnt-cluster search-tags web-fsn
    /cluster htools:iextags:web-fsn
    /instances/web-fsn-01.torproject.org web-fsn
    /instances/web-fsn-02.torproject.org web-fsn

## Adding and removing addresses on instances

Say you created an instance but forgot to need to assign an extra
IP. You can still do so with:

    gnt-instance modify --net -1:add,ip=116.202.120.174,network=gnt-fsn test01.torproject.org

## Pager playbook

### I/O overload

In case of excessive I/O, it might be worth looking into which machine
is in cause. The [[drbd]] page explains how to map a DRBD device to a
VM. You can also find which logical volume is backing an instance (and
vice versa) with this command:

    lvs -o+tags

This will list all logical volumes and their associated tags. If you
already know which logical volume you're looking for, you can address
it directly:

    root@fsn-node-01:~# lvs -o tags /dev/vg_ganeti_hdd/4091b668-1177-41ac-9310-1eac45b46620.disk2_data
      LV Tags
      originstname+bacula-director-01.torproject.org

### Node failures

Ganeti clusters are designed to be [self-healing](http://docs.ganeti.org/ganeti/2.15/html/admin.html#autorepair). As long as only
one machine disappears, the cluster should be able to recover by
failing over other nodes. This is currently done manually, see the
migrate section above.

This could eventually be automated if such situations occur more
often, by scheduling a [harep](http://docs.ganeti.org/ganeti/2.15/man/harep.html) cron job, which isn't enabled in
Debian by default. See also the [autorepair](http://docs.ganeti.org/ganeti/2.15/html/admin.html#autorepair) section of the admin
manual.

### Other troubleshooting

Riseup has [documentation on various failure scenarios](https://we.riseup.net/riseup+tech/ganeti#failure-scenarios) including
master failover, which we haven't tested. There's also upstream
documentation on [changing node roles](http://docs.ganeti.org/ganeti/2.15/html/admin.html#changing-the-node-role) which might be useful for a
master failover scenario.

The [walkthrough](http://docs.ganeti.org/ganeti/2.15/html/walkthrough.html) also has a few recipes to resolve common
problems.

## Disaster recovery

If things get completely out of hand and the cluster becomes too
unreliable for service, the only solution is to rebuild another one
elsewhere. Since Ganeti 2.2, there is a [move-instance](http://docs.ganeti.org/ganeti/2.15/html/move-instance.html) command to
move instances between cluster that can be used for that purpose.

If Ganeti is completely destroyed and its APIs don't work anymore, the
last resort is to restore all virtual machines from
[[backup]]. Hopefully, this should not happen except in the case of a
catastrophic data loss bug in Ganeti or [[drbd]].

# Reference

## Installation

### New node

- To create a new box, follow [[new-machine-hetzner-robot]] but change
  the following settings:

  * Server: [PX62-NVMe][]
  * Location: `FSN1`
  * Operating system: Rescue
  * Additional drives: 2x10TB
  * Add in the comment form that the server needs to be in the same
    datacenter as the other machines (FSN1-DC13, but double-check)

[PX62-NVMe]: https://www.hetzner.com/dedicated-rootserver/px62-nvme?country=OTHER

- follow the [[new-machine]] post-install configuration

- Network setup:

  1. Add the server to the two `vSwitch` systems in [Hetzner Robot web UI](https://robot.your-server.de/vswitch)

  2. install openvswitch and allow modules to be loaded

         touch /etc/no_modules_disabled
         reboot
         apt install openvswitch-switch

  3. Allocate a private IP address in the `30.172.in-addr.arpa` zone for
     the node.

  4. copy over the `/etc/network/interfaces` from another ganeti node,
     changing the `address` and `gateway` fields to match the local
     entry.

  5. knock on wood, cross your fingers, pet a cat, help your local
     book store, and reboot:
  
         reboot

- Prepare all the nodes by configuring them in puppet.  They should be
  in the class `roles::ganeti::fsn` if they are part of the fsn
  cluster.

- Re-enable modules disabling:

        rm /etc/no_modules_disabled

- reboot again

Then the node is ready to be added to the cluster, by running this on
the master node:

    puppet agent -t
    gnt-node add \
      --secondary-ip 172.30.135.2 \
      --no-ssh-key-check \
      --no-node-setup \
      fsn-node-02.torproject.org

If this is an entirely new cluster, you need a different procedure:

    gnt-cluster init \
      --master-netdev vlan-gntbe \
      --vg-name vg_ganeti \
      --secondary-ip 172.30.135.1 \
      --enabled-hypervisors kvm \
      --nic-parameters link=br0,vlan=4000 \
      --mac-prefix 00:66:37 \
      --no-ssh-init \
      --no-etc-hosts \
      fsngnt.torproject.org

The above assumes that `fsngnt` is already in DNS.

### cluster config

These could probably be merged into the cluster init, but just to document what has been done:

    gnt-cluster modify --reserved-lvs vg_ganeti/root,vg_ganeti/swap
    gnt-cluster modify -H kvm:kernel_path=,initrd_path=,
    gnt-cluster modify -H kvm:security_model=pool
    gnt-cluster modify -H kvm:kvm_extra='-device virtio-rng-pci\,bus=pci.0\,addr=0x1e\,max-bytes=1024\,period=1000'
    gnt-cluster modify -H kvm:disk_cache=none
    gnt-cluster modify -H kvm:disk_discard=unmap
    gnt-cluster modify -H kvm:scsi_controller_type=virtio-scsi-pci
    gnt-cluster modify -H kvm:disk_type=scsi-hd
    gnt-cluster modify --uid-pool 4000-4019
    gnt-cluster modify --nic-parameters mode=openvswitch,link=br0,vlan=4000
    gnt-cluster modify -D drbd:c-plan-ahead=0,disk-custom='--c-plan-ahead 0'
    gnt-cluster modify -H kvm:migration_bandwidth=950
    gnt-cluster modify -H kvm:migration_downtime=500

### Network configuration

IP allocation is managed by Ganeti through the `gnt-network(8)`
system. Say we have `192.0.2.0/24` reserved for the cluster, with
the host IP `192.0.2.100`` and the gateway on `192.0.2.1`. You will
create this network with:

    gnt-network add --network 192.0.2.0/24 --gateway 192.0.2.1 --network6 2001:db8::/32 --gateway6 fe80::1 example-network

Then we associate the new network to the default node group:

    gnt-network connect --nic-parameters=link=br0,vlan=4000,mode=openvswitch example-network default

The arguments to `--nic-parameters` come from the values configured in
the cluster, above. The current values can be found with `gnt-cluster
info`.

## SLA

As long as the cluster is not over capacity, it should be able to
survive the loss of a node in the cluster unattended.

Justified machines can be provisionned within a few business days
without problems.

New nodes can be provisioned within a week or two, depending on budget
and hardware availability.

## Design

Our first Ganeti cluster (`gnt-fsn`) is made of multiple machines
hosted with [Hetzner Robot](https://robot.your-server.de/), Hetzner's dedicated server hosting
service. All machines use the same hardware to avoid problems with
live migration. That is currently a customized build of the
[PX62-NVMe][] line.

### Network layout

Machines are interconnected over a [vSwitch](https://wiki.hetzner.de/index.php/Vswitch/en), a "virtual layer 2
network" probably implemented using [Software-defined Networking](https://en.wikipedia.org/wiki/Software-defined_networking)
(SDN) on top of Hetzner's network. The details of that implementation
do not matter much to us, since we do not trust the network and run an
IPsec layer on top of the vswitch. We communicate with the `vSwitch`
through [Open vSwitch](https://en.wikipedia.org/wiki/Open_vSwitch) (OVS), which is (currently manually)
configured on each node of the cluster.

There are two distinct IPsec networks:

 * `gnt-fsn-public`: the public network, which maps to the
   `fsn-gnt-inet-vlan` vSwitch at Hetzner, the `vlan-gntinet` OVS
   network, and the `gnt-fsn` network pool in Ganeti. it provides
   public IP addresses and routing across the network. instances get
   IP allocated in this network.

 * `gnt-fsn-be`: the private ganeti network which maps to the
   `fsn-gnt-backend-vlan` vSwitch at Hetzner and the `vlan-gntbe` OVS
   network. it has no matching `gnt-network` component and IP
   addresses are allocated manually in the 172.30.135.0/24 network
   through DNS. it provides internal routing for Ganeti commands and
   [[drbd]] storage mirroring.

### Hardware variations

We considered experimenting with the new AX line ([AX51-NVMe](https://www.hetzner.com/dedicated-rootserver/ax51-nvme?country=OTHER)) but
in the past DSA had problems live-migrating (it wouldn't immediately
fail but there were "issues" after). So we might need to [failover](http://docs.ganeti.org/ganeti/2.15/man/gnt-instance.html#failover)
instead of migrate between those parts of the cluster. There are also
doubts that the Linux kernel supports those shiny new processors at
all: similar processors had [trouble booting before Linux 5.5](https://www.phoronix.com/scan.php?page=news_item&px=Threadripper-3000-MCE-5.5-Fix) for
example, so it might be worth waiting a little before switching to
that new platform, even if it's cheaper. See the cluster configuration
section below for a larger discussion of CPU emulation.

### CPU emulation

Note that we might want to tweak the `cpu_type` parameter. By default,
it emulates a lot of processing that can be delegated to the host CPU
instead. If we use `kvm:cpu_type=host`, then each node will tailor the
emulation system to the CPU on the node. But that might make the live
migration more brittle: VMs or processes can crash after a live
migrate because of a slightly different configuration (microcode, CPU,
kernel and QEMU versions all play a role). So we need to find the
lowest common demoninator in CPU families. The list of available
families supported by QEMU varies between releases, but is visible
with:

    # qemu-system-x86_64 -cpu help
    Available CPUs:
    x86 486
    x86 Broadwell             Intel Core Processor (Broadwell)
    [...]
    x86 Skylake-Client        Intel Core Processor (Skylake)
    x86 Skylake-Client-IBRS   Intel Core Processor (Skylake, IBRS)
    x86 Skylake-Server        Intel Xeon Processor (Skylake)
    x86 Skylake-Server-IBRS   Intel Xeon Processor (Skylake, IBRS)
    [...]

The current [PX62 line][PX62-NVMe] is based on the [Coffee Lake](https://en.wikipedia.org/wiki/Coffee_Lake) Intel
micro-architecture. The closest matching family would be
`Skylake-Server` or `Skylake-Server-IBRS`, [according to wikichip](https://en.wikichip.org/wiki/intel/microarchitectures/coffee_lake#Compiler_support).
Note that newer QEMU releases (4.2, currently in unstable) have more
supported features.

In that context, of course, supporting different CPU manufacturers
(say AMD vs Intel) is impractical: they will have totally different
families that are not compatible with each other. This will break live
migration, which can trigger crashes and problems in the migrated
virtual machines.

If there are problems live-migrating between machines, it is still
possible to "failover" (`gnt-instance failover` instead of `migrate`)
which shuts off the machine, fails over disks, and starts it on the
other side. That's not such of a big problem: we often need to reboot
the guests when we reboot the hosts anyways. But it does complicate
our work. Of course, it's also possible that live migrates work fine
if *no* `cpu_type` at all is specified in the cluster, but that needs
to be verified.

Nodes could also [grouped](http://docs.ganeti.org/ganeti/2.15/man/gnt-group.html) to limit (automated) live migration to a
subset of nodes.

References:

 * <https://dsa.debian.org/howto/install-ganeti/>
 * <https://qemu.weilnetz.de/doc/qemu-doc.html#recommendations_005fcpu_005fmodels_005fx86>

### Installer

The [ganeti-instance-debootstrap](https://tracker.debian.org/pkg/ganeti-instance-debootstrap) package is used to install
instances. It is configured through Puppet with the [shared ganeti
module](https://forge.puppet.com/smash/ganeti), which deploys a few hooks to automate the install as much
as possible. The installer will:

 1. setup grub to respond on the serial console
 2. setup and log a random root password
 3. make sure SSH is installed and log the public keys and
    fingerprints
 4. setup swap if a labeled partition is present, or a 512MB swapfile
    otherwise
 5. setup basic static networking through `/etc/network/interfaces.d`

We have custom configurations on top of that to:

 1. add a few base packages
 2. do our own custom SSH configuration
 3. fix the hostname to be a FQDN
 4. add a line to `/etc/hosts`
 5. add a tmpfs

There is work underway to refactor and automate the install better,
see [ticket 31239](https://trac.torproject.org/projects/tor/ticket/31239) for details.

## Issues

There is no issue tracker specifically for this project, [File][] or
[search][] for issues in the [generic internal services][search] component.

 [File]: https://trac.torproject.org/projects/tor/newticket?component=Internal+Services%2FTor+Sysadmin+Team
 [search]: https://trac.torproject.org/projects/tor/query?status=!closed&component=Internal+Services%2FTor+Sysadmin+Team

# Discussion

## Overview

The project of creating a Ganeti cluster for Tor has appeared in the
summer of 2019. The machines were delivered by Hetzner in July 2019
and setup by weasel by the end of the month.

## Goals

The goal was to replace the aging group of KVM servers (kvm[1-5], AKA
textile, unifolium, macrum, kvm4 and kvm5).

### Must have

 * arbitrary virtual machine provisionning
 * redundant setup
 * automated VM installation
 * replacement of existing infrastructure

### Nice to have

 * fully configured in Puppet
 * full high availability with automatic failover
 * extra capacity for new projects

### Non-Goals

 * Docker or "container" provisionning - we consider this out of scope
   for now
 * self-provisionning by end-users: TPA remains in control of
   provisionning

## Approvals required

A budget was proposed by weasel in may 2019 and approved by Vegas in
June. An extension to the budget was approved in january 2020 by
Vegas.

## Proposed Solution

Setup a Ganeti cluster of two machines with a Hetzner vSwitch backend.

## Cost

The design based on the [PX62 line][PX62-NVMe] has the following monthly cost
structure:

 * per server: 118EUR (79EUR + 39EUR for 2x10TB HDDs)
 * IPv4 space: 35.29EUR (/27)
 * IPv6 space: 8.40EUR (/64)
 * bandwidth cost: 1EUR/TB (currently 38EUR)

At three servers, that adds up to around 435EUR/mth. Up to date costs
are available in the [Tor VM hosts.xlsx](https://nc.torproject.net/apps/onlyoffice/5395) spreadsheet.

## Alternatives considered

<!-- include benchmarks and procedure if relevant -->