ganeti.md

[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_]]

# 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, we use the following terms:

 * **node** a physical machine is called a *node* and a
 * **instance** a virtual machine
 * **master**: a *node* where on which we issue Ganeti commands and
   that supervises all the other nodes

Nodes are interconnected through a private network that is used to
communicate commands and synchronise disks (with
[howto/drbd](howto/drbd)). Instances are normally assigned two nodes:
a *primary* and a *secondary*: the *primary* is where the virtual
machine actually runs and the *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 with 10G root, 2G swap, 20G spare on SSD, 800G on HDD, 8GB
ram and 2 CPU cores:

    gnt-instance add \
      -o debootstrap+bullseye \
      -t drbd --no-wait-for-sync \
      --net 0:ip=pool,network=gnt-fsn13-02 \
      --no-ip-check \
      --no-name-check \
      --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 \
      test-01.torproject.org

### What that does

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`. TODO: configure disk 2
   and 3 automatically in installer. (`/var` and `/srv`?)
 * 8GB 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 `test-01.torproject.org` hostname

### Next steps

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)

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) or in our own reverse zone
files (if delegated).

Then follow [howto/new-machine](howto/new-machine).

### Known issues

 * **allocator failures**: Note that you may need to use the `--node`
   parameter to pick on which machines you want the machine to end up,
   otherwise Ganeti will choose for you (and may fail). Use, for
   example, `--node fsn-node-01:fsn-node-02` to use `node-01` as
   primary and `node-02` as secondary. The allocator can sometimes
   fail if the allocator is upset about something in the cluster, for
   example:
    
        Can's find primary node using iallocator hail: Request failed: No valid allocation solutions, failure reasons: FailMem: 2, FailN1: 2

   This situation is covered by [ticket 33785](https://bugs.torproject.org/33785). If this problem
   occurs, it might be worth [rebalancing the cluster](#rebalancing-a-cluster).

 * **ping failure**: 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). Note that this was fixed
   in Debian bullseye and later.

### Other examples

This is the same without the HDD partition, in the `gnt-chi` cluster:

    gnt-instance add \
      -o debootstrap+bullseye \
      -t drbd --no-wait-for-sync \
      --net 0:ip=pool,network=gnt-chi-01 \
      --no-ip-check \
      --no-name-check \
      --disk 0:size=10G \
      --disk 1:size=2G,name=swap \
      --disk 2:size=20G \
      --backend-parameters memory=8g,vcpus=2 \
      test-01.torproject.org

A simple test machine, with only 1G of disk, ram, and 1 CPU, without
DRBD, in the FSN cluster:

    gnt-instance add \
          -o debootstrap+bullseye \
          -t plain --no-wait-for-sync \
          --net 0:ip=pool,network=gnt-fsn13-02 \
          --no-ip-check \
          --no-name-check \
          --disk 0:size=10G \
          --disk 1:size=2G,name=swap \
          --backend-parameters memory=1g,vcpus=1 \
          test-01.torproject.org

Do not forget to follow the [next steps](#next-steps), above.

### iSCSI integration

To create a VM with iSCSI backing, a disk must first be created on the
SAN, then adopted in a VM, which needs to be *reinstalled* on top of
that. This is typical how large disks are provisionned in the
`gnt-chi` cluster, in the [Cymru POP](howto/new-machine-cymru).

The following instructions assume you are on a node with an [iSCSI
initiator properly setup](howto/new-machine-cymru#iscsi-initiator-setup), and the [SAN cluster management tools
setup](howto/new-machine-cymru#san-management-tools-setup). It also assumes you are familiar with the `SMcli` tool, see
the [storage servers documentation](howto/new-machine-cymru#storage-servers) for an introduction on that.

This assumes you are creating a 500GB VM, partitioned on the Linux
host, *not* on the iSCSI volume. TODO: change those instructions to
create one volume per partition, so that those can be resized more
easily. The following is how `tb-build-03` was setup.

 1. create the disk on the SAN and assign it to the host group:

        puppet agent --disable "creating a SAN disk"
        $EDITOR /usr/local/sbin/tpo-create-san-disks
        /usr/local/sbin/tpo-create-san-disks
        puppet agent --enable

    WARNING: the above script needs to be edited before it does the
    right thing. It will show the LUN numbers in use below. This,
    obviously, is not ideal, and should be replaced by a Ganeti
    external storage provider.

    NOTE: the `logicalUnitNumber` here must be an increment from the
    previous highest LUN. See also the [disk creation instructions](howto/new-machine-cymru#creating-a-disk)
    for a discussion.

 2. configure the disk on all Ganeti nodes, in Puppet's
    `profile::ganeti::chi` class:

        iscsi::multipath::alias { 'web-chi-03':
          wwid => '36782bcb00063c6a500000d67603f7abf',
        }

 3. propagate the magic to all nodes in the cluster:
 
        gnt-cluster command "puppet agent -t ; iscsiadm -m node --rescan ; multipath -r"

 4. confirm that multipath works, it should look something like this":

        root@chi-node-01:~# multipath -ll
        web-chi-03-srv (36782bcb00063c6a500000d67603f7abf) dm-20 DELL,MD32xxi
        size=500G features='5 queue_if_no_path pg_init_retries 50 queue_mode mq' hwhandler='1 rdac' wp=rw
        |-+- policy='round-robin 0' prio=6 status=active
        | |- 11:0:0:4 sdi 8:128 active ready running
        | |- 12:0:0:4 sdj 8:144 active ready running
        | `- 9:0:0:4  sdh 8:112 active ready running
        `-+- policy='round-robin 0' prio=1 status=enabled
          |- 10:0:0:4 sdk 8:160 active ghost running
          |- 7:0:0:4  sdl 8:176 active ghost running
          `- 8:0:0:4  sdm 8:192 active ghost running
        root@chi-node-01:~#

    and the device `/dev/mapper/web-chi-03` should exist.

 6. adopt the disks in Ganeti:

        gnt-instance add \
              -n chi-node-04.torproject.org \
              -o debootstrap+bullseye \
              -t blockdev --no-wait-for-sync \
              --net 0:ip=pool,network=gnt-chi-01 \
              --no-ip-check \
              --no-name-check \
              --disk 0:adopt=/dev/disk/by-id/dm-name-tb-build-03-root \
              --disk 1:adopt=/dev/disk/by-id/dm-name-tb-build-03-swap,name=swap \
              --disk 2:adopt=/dev/disk/by-id/dm-name-tb-build-03-srv \
              --backend-parameters memory=16g,vcpus=8 \
              tb-build-03.torproject.org

    NOTE: the actual node must be manually picked because the `hail`
    allocator doesn't seem to know about block devices.

 7. at this point, the VM probably doesn't boot, because for some
    reason the `gnt-instance-debootstrap` doesn't fire when disks are
    adopted. so you need to reinstall the machine, which involves
    stopping it first:

        gnt-instance shutdown --timeout=0 tb-build-03
        gnt-instance reinstall tb-build-03

    HACK: the current installer fails on weird partionning errors, see
    [upstream bug 13](https://github.com/ganeti/instance-debootstrap/issues/13). We applied [patch 14](https://github.com/ganeti/instance-debootstrap/pull/14) on `chi-node-04`
    and sent it upstream for review before committing to maintaining
    this in Debian or elsewhere. It should be tested on other installs
    beforehand as well.

From here on, follow the [next steps](#next-steps) above.

TODO: This would ideally be automated by an external storage provider,
see the [storage reference for more information](#storage).

### Troubleshooting

If a Ganeti instance install fails, it will show the end of the
install log, for example:

```
Thu Aug 26 14:11:09 2021  - INFO: Selected nodes for instance tb-pkgstage-01.torproject.org via iallocator hail: chi-node-02.torproject.org, chi-node-01.torproject.org
Thu Aug 26 14:11:09 2021  - INFO: NIC/0 inherits netparams ['br0', 'bridged', '']
Thu Aug 26 14:11:09 2021  - INFO: Chose IP 38.229.82.29 from network gnt-chi-01
Thu Aug 26 14:11:10 2021 * creating instance disks...
Thu Aug 26 14:12:58 2021 adding instance tb-pkgstage-01.torproject.org to cluster config
Thu Aug 26 14:12:58 2021 adding disks to cluster config
Thu Aug 26 14:13:00 2021 * checking mirrors status
Thu Aug 26 14:13:01 2021  - INFO: - device disk/0: 30.90% done, 3m 32s remaining (estimated)
Thu Aug 26 14:13:01 2021  - INFO: - device disk/2:  0.60% done, 55m 26s remaining (estimated)
Thu Aug 26 14:13:01 2021 * checking mirrors status
Thu Aug 26 14:13:02 2021  - INFO: - device disk/0: 31.20% done, 3m 40s remaining (estimated)
Thu Aug 26 14:13:02 2021  - INFO: - device disk/2:  0.60% done, 52m 13s remaining (estimated)
Thu Aug 26 14:13:02 2021 * pausing disk sync to install instance OS
Thu Aug 26 14:13:03 2021 * running the instance OS create scripts...
Thu Aug 26 14:16:31 2021 * resuming disk sync
Failure: command execution error:
Could not add os for instance tb-pkgstage-01.torproject.org on node chi-node-02.torproject.org: OS create script failed (exited with exit code 1), last lines in the log file:
Setting up openssh-sftp-server (1:7.9p1-10+deb10u2) ...
Setting up openssh-server (1:7.9p1-10+deb10u2) ...
Creating SSH2 RSA key; this may take some time ...
2048 SHA256:ZTeMxYSUDTkhUUeOpDWpbuOzEAzOaehIHW/lJarOIQo root@chi-node-02 (RSA)
Creating SSH2 ED25519 key; this may take some time ...
256 SHA256:MWKeA8vJKkEG4TW+FbG2AkupiuyFFyoVWNVwO2WG0wg root@chi-node-02 (ED25519)
Created symlink /etc/systemd/system/sshd.service \xe2\x86\x92 /lib/systemd/system/ssh.service.
Created symlink /etc/systemd/system/multi-user.target.wants/ssh.service \xe2\x86\x92 /lib/systemd/system/ssh.service.
invoke-rc.d: could not determine current runlevel
Setting up ssh (1:7.9p1-10+deb10u2) ...
Processing triggers for systemd (241-7~deb10u8) ...
Processing triggers for libc-bin (2.28-10) ...
Errors were encountered while processing:
 linux-image-4.19.0-17-amd64
E: Sub-process /usr/bin/dpkg returned an error code (1)
run-parts: /etc/ganeti/instance-debootstrap/hooks/ssh exited with return code 100
Using disk /dev/drbd4 as swap...
Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=96111754-c57d-43f2-83d0-8e1c8b4688b4
Not using disk 2 (/dev/drbd5) because it is not named 'swap' (name: )
root@chi-node-01:~#
```

Here the failure which tripped the install is:

```
Errors were encountered while processing:
 linux-image-4.19.0-17-amd64
E: Sub-process /usr/bin/dpkg returned an error code (1)
```

But the actual error is higher up, and we need to go look at the logs
on the server for this, in this case in
`chi-node-02:/var/log/ganeti/os/add-debootstrap+buster-tb-pkgstage-01.torproject.org-2021-08-26_14_13_04.log`,
we can find the real problem:

```
Setting up linux-image-4.19.0-17-amd64 (4.19.194-3) ...
/etc/kernel/postinst.d/initramfs-tools:
update-initramfs: Generating /boot/initrd.img-4.19.0-17-amd64
W: Couldn't identify type of root file system for fsck hook
/etc/kernel/postinst.d/zz-update-grub:
/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).
run-parts: /etc/kernel/postinst.d/zz-update-grub exited with return code 1
dpkg: error processing package linux-image-4.19.0-17-amd64 (--configure):
 installed linux-image-4.19.0-17-amd64 package post-installation script subprocess returned error exit status 1
```

In this case, oddly enough, even though Ganeti thought the install had
failed, the machine can actually start:

```
gnt-instance start tb-pkgstage-01.torproject.org
```

... and after a while, we can even get a console:

```
gnt-instance start tb-pkgstage-01.torproject.org
```

And in *that* case, the procedure can just continue from here on:
reset the root password, and just make sure you finish the install:

```
apt install linux-image-amd64
```

In the above case, the `sources-list` post-install hook was buggy: it
wasn't mounting `/dev` and friends before launching the upgrades,
which was causing issues when a kernel upgrade was queued.

And *if* you are debugging an installer and by mistake end up with
half-open filesystems and stray DRBD devices, do take a look at the
[LVM](howto/lvm) and [DRBD documentation](howto/drbd).

## Modifying an instance

### CPU, memory changes

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=4 test1.torproject.org
    gnt-instance modify -B memory=8g test1.torproject.org
    gnt-instance reboot test1.torproject.org

### IP address change

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

### Resizing disks

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 --absolute test1.torproject.org 0 16g
    gnt-instance reboot test1.torproject.org

The number `0` in this context, indicates the first disk of the
instance.  The amount specified is the final disk size (because of the
`--absolute` flag). In the above example, the final disk size will be
16GB. To *add* space to the existing disk, remove the `--absolute`
flag:

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

In the above example, 16GB will be **ADDED** to the disk. Be careful
with resizes, because it's not possible to revert such a change:
`grow-disk` does support shrinking disks. The only way to revert the
change is by exporting / importing the instance.

Note the reboot, above, will impose a downtime. See [upstream bug
28](https://github.com/ganeti/ganeti/issues/28) about improving that.

Then the filesystem needs to be resized inside the VM:

    ssh root@test1.torproject.org 

#### Resizing under LVM

Use `pvs` to display information about the physical volumes:

    root@cupani:~# pvs
    PV         VG        Fmt  Attr PSize   PFree   
    /dev/sdc   vg_test   lvm2 a--  <8.00g  1020.00m

Resize the physical volume to take up the new space:

    pvresize /dev/sdc

Use `lvs` to display information about logical volumes:

    # lvs
    LV            VG               Attr       LSize    Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
    var-opt       vg_test-01     -wi-ao---- <10.00g                                                    
    test-backup vg_test-01_hdd   -wi-ao---- <20.00g            

Use lvextend to add space to the volume:

    lvextend -l '+100%FREE' vg_test-01/var-opt

Finally resize the filesystem:

    resize2fs /dev/vg_test-01/var-opt

See also the [LVM howto](howto/lvm).

#### Resizing without LVM, no partitions

If there's no LVM inside the VM (a more common configuration
nowadays), the above procedure will obviously not work. If this is a
secondary disk (e.g. `/dev/sdc`) there is a good chance a partition
was created directly on it and that you do not need to repartition the
drive. This is an example of a good configuration if we want to resize
`sdc`:

```
root@bacula-director-01:~# lsblk 
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
fd0      2:0    1    4K  0 disk 
sda      8:0    0   10G  0 disk 
└─sda1   8:1    0   10G  0 part /
sdb      8:16   0    2G  0 disk [SWAP]
sdc      8:32   0  250G  0 disk /srv
```

Note that if we would need to resize `sda`, we'd have to follow the
other procedure, in the next section.

If we check the free disk space on the device we will notice it has
not changed yet:

```
# df -h /srv
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdc        196G  160G   27G  86% /srv
```

The resize is then simply:

```
# resize2fs /dev/sdc
resize2fs 1.44.5 (15-Dec-2018)
Filesystem at /dev/sdc is mounted on /srv; on-line resizing required
old_desc_blocks = 25, new_desc_blocks = 32
The filesystem on /dev/sdc is now 65536000 (4k) blocks long.
```

Read on for the most complicated scenario.

#### Resizing without LVM, with partitions

If the filesystem to resize is not *directly* on the device, you will
need to resize the partition manually, which can be done using
fdisk. In the following example we have a `sda1` partition that we
want to extend from 10G to 20G to fill up the free space on
`/dev/sda`. Here is what the partition layout looks like before the
resize:

```
# lsblk -a
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
fd0      2:0    1   4K  0 disk 
sda      8:0    0  20G  0 disk 
└─sda1   8:1    0  10G  0 part /
sdb      8:16   0   2G  0 disk [SWAP]
sdc      8:32   0  40G  0 disk /srv
```

We use fdisk on the device:

```
# fdisk /dev/sda

Welcome to fdisk (util-linux 2.33.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p # prints the partition table
Disk /dev/sda: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: QEMU HARDDISK   
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x73ab5f76

Device     Boot Start      End  Sectors Size Id Type
/dev/sda1  *     2048 20971519 20969472  10G 83 Linux # note the starting sector for later

```

Now we delete the partition. Note that the data will not be deleted, only the partition table will be altered:

```
Command (m for help): d
Selected partition 1
Partition 1 has been deleted.

Command (m for help): p
Disk /dev/sda: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: QEMU HARDDISK   
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x73ab5f76
```

Now we create the new partition to take up the whole space:

```
Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-41943039, default 2048): 2048 # this is the starting sector from above.
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-41943039, default 41943039): 41943039

Created a new partition 1 of type 'Linux' and of size 20 GiB.
Partition #1 contains a ext4 signature.

Do you want to remove the signature? [Y]es/[N]o: n # we want to keep the previous signature

Command (m for help): p

Disk /dev/sda: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: QEMU HARDDISK   
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x73ab5f76

Device     Boot Start      End  Sectors Size Id Type
/dev/sda1        2048 41943039 41940992  20G 83 Linux

Command (m for help): w
The partition table has been altered.
Syncine disks.
```

Now we check the partitions:

```
# lsblk -a
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
fd0      2:0    1   4K  0 disk 
sda      8:0    0  20G  0 disk 
└─sda1   8:1    0  20G  0 part /
sdb      8:16   0   2G  0 disk [SWAP]
sdc      8:32   0  40G  0 disk /srv
```

If we check the free disk space on the device we will notice it has not changed  yet:

```
# df -h /
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       9.8G  8.5G  874M  91% /
```

We need to resize it:

```
# resize2fs /dev/sda1
resize2fs 1.44.5 (15-Dec-2018)
Filesystem at /dev/sda1 is mounted on /; on-line resizing required
old_desc_blocks = 2, new_desc_blocks = 3
The filesystem on /dev/sda1 is now 5242624 (4k) blocks long.
```

The resize is now complete.

#### Resizing an iSCSI LUN

Growing a disk hosted on a iSCSI SAN like the Dell PowerVault MD3200i involves
several steps beginning with resizing the LUN itself.

First, we identify how much space is available on the virtual disks' diskGroup:

    # SMcli -n chi-san-01 -c "show allVirtualDisks summary;"

	STANDARD VIRTUAL DISKS SUMMARY
	Number of standard virtual disks: 5

	Name                Thin Provisioned     Status     Capacity     Accessible by       Source
	example-01-srv      No                   Optimal    700.000 GB   Host Group gnt-chi  Disk Group 5

This shows that `tb-build-03-srv` is hosted on Disk Group "5":

    # SMcli -n chi-san-01 -c "show diskGroup [5];"

    DETAILS

       Name:              5

          Status:         Optimal
          Capacity:       1,852.026 GB
          Current owner:  RAID Controller Module in slot 1

          Data Service (DS) Attributes

             RAID level:                    5
             Physical Disk media type:      Physical Disk
             Physical Disk interface type:  Serial Attached SCSI (SAS)
             Enclosure loss protection:     No
             Secure Capable:                No
             Secure:                        No


          Total Virtual Disks:          1
             Standard virtual disks:    1
             Repository virtual disks:  0
             Free Capacity:             1,152.026 GB

          Associated physical disks - present (in piece order)
          Total physical disks present: 3

             Enclosure     Slot
             0             6
             1             11
             0             7

`Free Capacity` indicates about 1,5 TB of free space available. So we can go
ahead with the actual resize:

    # SMcli -n chi-san-01 -p $PASSWORD -c "set virtualdisk [\"example-01-srv\"] addCapacity=100GB;"

Next, on the instance's primary node we need to tell `iscsiadm` to rescan the
LUN. To do this we first need to learn the iSCSI `targetname` we need to run the
rescan command against.

    # multipath -ll

This shows which device nodes (eg. `sdw`) are associated with the volume we need
to resize. There are usually six such nodes for each iSCSI LUN, and they will be
listed under the same "Target:" header in the output of the next command:

    # iscsiadm -m session -P 3 | grep -e ^Target -e 'Attached scsi disk' -e 'Current Portal'

To trigger the iSCSI rescan:

    # iscsiadm -m node --targetname iqn.foo.org.example -R

The success of this step can be validated by looking at the output of `lsblk`:
the device nodes associated with the LUN should now display the new size.

Next, we need to also *kick* `multipathd` to make it rescan the iSCSI LUN. The
volume name used here must correspond to the volume name in the output of
`multipath -ll`.

    # multipathd -v3 -k"resize map example-01-srv"

Another look at the output of `multipath -ll` should confirm the volume now
reflects the new size of the underlying iSCSI LUN.

In order for ganeti/qemu to make this extra space available to the instance, a
reboot must be performed from outside the instance.

Depending on whether LVM volumes or partitions are used within the VM, there
could be extra steps required before running the `resize2fs` command. See the
instructions above for details on how to resize those bits.

### Adding disks

A disk can be added to an instance with the `modify` command as
well. This, for example, will add a 100GB disk to the `test1` instance
on teh `vg_ganeti_hdd` volume group, which is "slow" rotating disks:

    gnt-instance modify --disk add:size=100g,vg=vg_ganeti_hdd test1.torproject.org
    gnt-instance reboot test1.torproject.org

### Changing disk type

If you have, say, a test instance that was created with a `plain` disk
template but we actually want it in production, with a `drbd` disk
template. Switching to `drbd` is easy:

    gnt-instance shutdown test-01
    gnt-instance modify -t drbd test-01
    gnt-instance start test-01

The second command will use the allocator to find a secondary node. If
that fails, you can assign a node manually with `-n`.

You can also switch back to `plain`, although you should generally
never do that.

See also the [upstream procedure](https://docs.ganeti.org/docs/ganeti/3.0/html/admin.html#conversion-of-an-instance-s-disk-type) and [design document](https://docs.ganeti.org/docs/ganeti/3.0/html/design-disk-conversion.html).

### Adding a network interface on the rfc1918 vlan

We have a vlan that some VMs that do not have public addresses sit on.
Its vlanid is 4002 and its backed by Hetzner vswitch vSwitch #11973 "fsn-gnt-rfc1918-traffic".
Note that traffic on this vlan will travel in the clear between nodes.

To add an instance to this vlan, give it a second network interface using

    gnt-instance modify --net add:link=br0,vlan=4002,mode=openvswitch test1.torproject.org

## Destroying an instance

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

    gnt-instance remove test01.torproject.org

## Getting information

Information about an instances can be found in the rather verbose
`gnt-instance info`:

    root@fsn-node-01:~# gnt-instance info tb-build-02.torproject.org
    - Instance name: tb-build-02.torproject.org
      UUID: 8e9f3ca6-204f-4b6c-8e3e-6a8fda137c9b
      Serial number: 5
      Creation time: 2020-12-15 14:06:41
      Modification time: 2020-12-15 14:07:31
      State: configured to be up, actual state is up
      Nodes: 
        - primary: fsn-node-03.torproject.org
          group: default (UUID 8c32fd09-dc4c-4237-9dd2-3da3dfd3189e)
        - secondaries: fsn-node-04.torproject.org (group default, group UUID 8c32fd09-dc4c-4237-9dd2-3da3dfd3189e)
      Operating system: debootstrap+buster

A quick command that can be done is this, which shows the
primary/secondary for a given instance:

    gnt-instance info tb-build-02.torproject.org | grep -A 3 Nodes

An equivalent command will show the primary and secondary for *all*
instances, on top of extra information (like the CPU count, memory and
disk usage):

    gnt-instance list -o pnode,snodes,name,be/vcpus,be/memory,disk_usage,disk_template,status | sort

It can be useful to run this in a loop to see changes:

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

## Disk operations (DRBD)

Instances should be setup using the DRBD backend, in which case you
should probably take a look at [howto/drbd](howto/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:

    gnt-instance list -o pnode,name,be/vcpus,be/memory,disk_usage,disk_template,status | sort &&
    echo &&
    gnt-node list

The latter does not show disk usage for secondary volume groups (see
[upstream issue 1379](https://github.com/ganeti/ganeti/issues/1379)), for a complete picture of disk usage, use:

    gnt-node list-storage

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

Also note the `hspace -L` command, which can tell you how many
instances can be created in a given cluster. It uses the "standard"
instance template defined in the cluster (which we haven't configured
yet).

## 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 libvirt 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
 * the `SPARE_NODE` has space in `/srv/` to host all the virtual
   machines to import, to check, use:

        fab -H crm-ext-01.torproject.org,crm-int-01.torproject.org,forrestii.torproject.org,nevii.torproject.org,rude.torproject.org,troodi.torproject.org,vineale.torproject.org libvirt.du -p kvm3.torproject.org | sed '/-swap$/d;s/ .*$//' <f | awk '{s+=$1} END {print s}'

   You will very likely need to create a `/srv` big enough for this,
   for example:

        lvcreate -L 300G vg_ganeti -n srv-tmp &&
        mkfs /dev/vg_ganeti/srv-tmp &&
        mount /dev/vg_ganeti/srv-tmp /srv

Import procedure:

 1. pick a viable SPARE NODE to import the INSTANCE (see "evaluating
    cluster capacity" above, when in doubt) and find on which KVM HOST
    the INSTANCE lives

 2. copy the disks, without downtime:
 
        ./ganeti -v -H $INSTANCE libvirt-import  --ganeti-node $SPARE_NODE --libvirt-host $KVM_HOST

 3. copy the disks again, this time suspending the machine:

        ./ganeti -v -H $INSTANCE libvirt-import  --ganeti-node $SPARE_NODE --libvirt-host $KVM_HOST --suspend --adopt

 4. renumber the host:
    
        ./ganeti -v -H $INSTANCE renumber-instance --ganeti-node $SPARE_NODE

 5. test services by changing your `/etc/hosts`, possibly warning
    service admins:

    > Subject: $INSTANCE IP address change planned for Ganeti migration
    >
    > I will soon migrate this virtual machine to the new ganeti cluster. this
    > will involve an IP address change which might affect the service.
    >
    > Please let me know if there are any problems you can think of. in
    > particular, do let me know if any internal (inside the server) or external
    > (outside the server) services hardcodes the IP address of the virtual
    > machine.
    >
    > A test instance has been setup. You can test the service by
    > adding the following to your /etc/hosts:
    >
    >     116.202.120.182 $INSTANCE
    >     2a01:4f8:fff0:4f:266:37ff:fe32:cfb2 $INSTANCE

 6. destroy test instance:
 
        gnt-instance remove $INSTANCE
 
 7. lower TTLs to 5 minutes. this procedure varies a lot according to
    the service, but generally if all DNS entries are `CNAME`s
    pointing to the main machine domain name, the TTL can be lowered
    by adding a `dnsTTL` entry in the LDAP entry for this host. For
    example, this sets the TTL to 5 minutes:
    
        dnsTTL: 300

    Then to make the changes immediate, you need the following
    commands:
    
        ssh root@alberti.torproject.org sudo -u sshdist ud-generate &&
        ssh root@nevii.torproject.org ud-replicate
 
    Warning: if you migrate one of the hosts ud-ldap depends on, this
    can fail and not only the TTL will not update, but it might also
    fail to update the IP address in the below procedure. See [ticket
    33766](https://bugs.torproject.org/33766) for
    details.
 
 8. shutdown original instance and redo migration as in step 3 and 4:
 
        fab -H $INSTANCE reboot.halt-and-wait --delay-shutdown 60 --reason='migrating to new server' &&
        ./ganeti -v -H $INSTANCE libvirt-import  --ganeti-node $SPARE_NODE --libvirt-host $KVM_HOST --adopt &&
        ./ganeti -v -H $INSTANCE renumber-instance --ganeti-node $SPARE_NODE

 9. final test procedure

    TODO: establish host-level test procedure and run it here.

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

         gnt-instance stop $INSTANCE &&
         gnt-instance modify -t drbd $INSTANCE &&
         gnt-instance failover -f $INSTANCE &&
         gnt-instance start $INSTANCE

     The above can sometimes fail if the allocator is upset about
     something in the cluster, for example:
     
         Can's find secondary node using iallocator hail: Request failed: No valid allocation solutions, failure reasons: FailMem: 2, FailN1: 2

     This situation is covered by [ticket 33785](https://bugs.torproject.org/33785). To work around the
     allocator, you can specify a secondary node directly:
     
         gnt-instance modify -t drbd -n fsn-node-04.torproject.org $INSTANCE &&
         gnt-instance failover -f $INSTANCE &&
         gnt-instance start $INSTANCE

     TODO: move into fabric, maybe in a `libvirt-import-live` or
     `post-libvirt-import` job that would also do the renumbering below

 11. change IP address in the following locations:

     * LDAP (`ipHostNumber` field, but also change the `physicalHost` and `l` fields!).  Also drop the dnsTTL attribute while you're at it.
     * 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)
     * nagios (don't forget to change the parent)
     * reverse DNS (upstream web UI, e.g. Hetzner Robot)
     * grep for the host's IP address on itself:

            grep -r -e 78.47.38.227  -e 2a01:4f8:fff0:4f:266:37ff:fe77:1ad8 /etc
            grep -r -e 78.47.38.227  -e 2a01:4f8:fff0:4f:266:37ff:fe77:1ad8 /srv

     * grep for the host's IP on *all* hosts:

            cumin-all-puppet
            cumin-all 'grep -r -e 78.47.38.227  -e 2a01:4f8:fff0:4f:266:37ff:fe77:1ad8 /etc'

     TODO: move those jobs into fabric