Single node support

[masnax]

Adds basic single-node support.

This adds an initial question to microcloud init asking if the user wants to set up just one node.

Do you want to set up more than one cluster member? (yes/no) [default=yes]: 

If the user enters no, the system will follow the ordinary setup with ZFS and OVN (or optionally a FAN network instead), but the user will not be prompted for a lookup subnet and will not be presented a list of systems.

The cluster can be grown after this point by using microcloud add.

TODO:

• Add tests
• Support preseed
• Support adding missing services (maybe, if it makes sense)
• Test MicroOVN functions properly with 1 node.

[masnax]

Right now, this assumes the current behaviour where MicroCeph requires 3 nodes. This can be configured, but will require changing a lot of the tests which check for MicroCeph to be skipped with fewer than 3 nodes.

Preseed is also ignored here. We arbitrarily require at least 2 nodes for preseed but this doesn't necessarily have to be the case anymore.

[roosterfish]

Looks good, only two small comments.

What is missing when it comes to adding existing services? Do you think about something like deploying a single node MicroCloud without OVN and then adding OVN to it later using service add?

Should the option of single node MicroCloud also be reflected in the docs? I was thinking about something like https://canonical-microcloud.readthedocs-hosted.com/en/latest/microovn/tutorial/single-node/.

The PRs description still says Ceph will be skipped but after #378 got merged I think this sentence can be removed too.

[roosterfish]

As mentioned earlier the only other thing I found with this PR is adding services (like MicroOVN) after the single node MicroCloud is deployed seems to be not working currently.

It reports Error: All services have already been set up:

root@m1:~# microcloud init
Waiting for LXD to start ...
Do you want to set up more than one cluster member? (yes/no) [default=yes]: no
Select an address for MicroCloud's internal traffic:

 Using address "10.165.133.71" for MicroCloud

Gathering system information ...
Would you like to set up local storage? (yes/no) [default=yes]:  
Select exactly one disk from each cluster member:

Select which disks to wipe:

 Using "/dev/disk/by-id/scsi-SQEMU_QEMU_HARDDISK_lxd_volm1--local" on "m1" for local storage pool

Would you like to set up distributed storage? (yes/no) [default=yes]: 
Select from the available unpartitioned disks:

Select which disks to wipe:

Disk configuration does not meet recommendations for fault tolerance. At least 3 systems must supply disks.
Continuing with this configuration will leave MicroCloud susceptible to data loss
Change disk selection? (yes/no) [default=yes]: no
 Using 1 disk(s) on "m1" for remote storage pool

Do you want to encrypt the selected disks? (yes/no) [default=no]: 
Would you like to set up CephFS remote storage? (yes/no) [default=yes]: 
What subnet (either IPv4 or IPv6 CIDR notation) would you like your Ceph internal traffic on? [default: 10.165.133.0/24] 
Configure distributed networking? (yes/no) [default=yes]: no
Initializing new services
 Local MicroCloud is ready
 Local LXD is ready
 Local MicroOVN is ready
 Local MicroCeph is ready
Awaiting cluster formation ...
Configuring cluster-wide devices ...
MicroCloud is ready
root@m1:~# microcloud service add
Error: All services have already been set up

[masnax]

@roosterfish Ah I see, it's just a miscommunication. microcloud service add does not let you re-configure services that are already clustered, it initializes new services that were not previously initialized.

For example, if MicroOVN was not installed when microcloud init was first run, but installed later. You can then use microcloud service add to add MicroOVN to the MicroCloud cluster.

You get the error Error: All services have already been set up because MicroOVN has already been initialized by MicroCloud during microcloud init, the configuration on the LXD side is what was skipped.

For example:

snap remove microovn --purge
microcloud init
...
snap install microovn
microcloud service add

We've been discussing adding a microcloud service edit to change the configuration of the already-installed services, but that likely won't be part of the LTS release.

[roosterfish]

You get the error Error: All services have already been set up because MicroOVN has already been initialized by MicroCloud during microcloud init, the configuration on the LXD side is what was skipped.

Thanks I see but is it a bug that MicroCloud initializes MicroOVN as you can see in the output above I have proactively answered no on the Configure distributed networking? question?

It gave me a single node MicroCloud using fan networking so I would suspect MicroCloud doesn't even look at MicroOVN in this situation.

[masnax]

You get the error Error: All services have already been set up because MicroOVN has already been initialized by MicroCloud during microcloud init, the configuration on the LXD side is what was skipped.

Thanks I see but is it a bug that MicroCloud initializes MicroOVN as you can see in the output above I have proactively answered no on the Configure distributed networking? question?

It gave me a single node MicroCloud using fan networking so I would suspect MicroCloud doesn't even look at MicroOVN in this situation.

Configure != Initialize. MicroCloud will form the MicroOVN cluster if the snap is installed irrespective of whether or not you want to configure the network in LXD at the precise moment you ran microcloud init. The primary objective is to create the clusters. If a user wants to configure their network some other way, then at least they will have the MicroOVN cluster formed.

[roosterfish]

LGTM!

[token47]

Sunbeam uses very similar approach and can do microceph in one node. Can't the same be done for microcloud?

[masnax]

Sunbeam uses very similar approach and can do microceph in one node. Can't the same be done for microcloud?

If you're referring to the line in the PR description about MicroCeph being skipped, that was out of date and is now removed. Single node does support MicroCeph.