Just as we’re wrapping up 2023, one last Incus release!
Incus 0.4 is now out, including keepalive support in the command line tool, improved certificate management, new OVN configuration keys and the ability to create CephFS filesystems directly through Incus!
This is going to be the last release of Incus to benefit from any of the work that goes into Canonical LXD as their decision to re-license will be preventing us from taking in any additional fixes or improvements. You’ll find details about that in one of my previous posts.
Related to that change, we’ve made the decision to progressively phase out access to the Linux Containers image server for those users still on Canonical LXD. You’ll find details about the motivations and timeline for this change here.
The full announcement and changelog can be found here. And for those who prefer videos, here’s the release overview video:
Finally just a quick reminder that my company is offering commercial support on Incus, ranging from by-the-hour support contracts to one-off services on things like initial migration from LXD, review of your deployment to squeeze the most out of Incus or even feature sponsorship. You’ll find all details of that here: https://zabbly.com/incus
Donations towards my work on this and other open source projects is also always appreciated, you can find me on Github Sponsors, Patreon and Ko-fi.
With this release, we finally got to spend less time on building up infrastructure and processes and more on working on meaningful improvements and new features with was really good to see!
This is also the first release with support for migrating LXD clusters over to Incus. The built-in lxd-to-incus migration tool can now handle most standalone and clustered cases, performing a full initial validation of all settings to avoid surprises.
The full announcement and changelog can be found here. And for those who prefer watching over reading, I’ve also recorded a video overview:
And lastly, my company is now offering commercial support on Incus, ranging from by-the-hour support contracts to one-off services on things like initial migration from LXD, review of your deployment to squeeze the most out of Incus or even feature sponsorship.
And for anyone who just wants to contribute a bit towards my work on this and other open source projects, you’ll also find me on Github Sponsors, Patreon and Ko-fi.
Over the past few posts, I covered the hardware I picked up to setup a small LXD cluster and get it all setup at a co-location site near home. I’ve then gone silent for about 6 months, not because anything went wrong but just because of not quite finding the time to come back and complete this story!
So let’s pick things up where I left them with the last post and cover the last few bits of the network setup and then go over what happened over the past 6 months.
Routing in a HA environment
You may recall that the 3 servers are both connected to a top of the rack switch (bonded dual-gigabit) as well as connected to each other (bonded dual-10-gigabit). The netplan config in the previous post would allow each of the servers to talk to the others directly and establish a few VLANs on the link to the top of the rack switch.
Those are for:
WAN-HIVE: Peering VLAN with my provider containing their core routers and mine
INFRA-UPLINK: OVN uplink network (where all the OVN virtual routers get their external addresses)
INFRA-HOSTS: VLAN used for external communication with the servers
INFRA-BMC: VLAN used for the management ports of the servers (BMCs) and switch, isolated from the internet
Simply put, the servers have their main global address and default gateway on INFRA-HOSTS, the BMCs and switch have their management addresses in INFRA-BMC, INFRA-UPLINK is consumed by OVN and WAN-HIVE is how I access the internet.
In my setup, I then run three containers, one on each server which each gets direct access to all those VLANs and act as a router using FRR. FRR is configured to establish BGP sessions with both of my provider’s core routers, getting routing to the internet that way and announcing my IPv4 and IPv6 subnets that way too.
On the internal side of things, I’m using VRRP to provide a virtual router internally. Typically this means that frr01 is the default gateway for all egress traffic while ingress traffic is somewhat spread across all 3 thanks to them having the same BGP weight (so my provider’s routers distribute the connections across all active peers).
With that in place, so long as one of the FRR instances are running, connectivity is maintained. This makes doing maintenance quite easy as there is effectively no SPOF.
Enter LXD networks with OVN
Now for where things get a bit trickier. As I’m using OVN to provide virtual networks inside of LXD, each of those networks will typically need some amount of public addressing. For IPv6, I don’t do NAT so each of my networks get a public /64 subnet. For IPv4, I have a limited number of those, so I just assign them one by one (/32) directly to specific instances.
Whenever such a network is created, it will grab an IPv4 and IPv6 address from the subnet configured on INFRA-UPLINK. That part is all good and the OVN gateway becomes immediately reachable.
The issue is with the public IPv6 subnet used by each network and with any additional addresses (IPv4 or IPv6) which are routed directly to its instances. For that to work, I need my routers to send the traffic headed for those subnets to the correct OVN gateway.
But how do you do that? Well, there are pretty much three options here:
You use LXD’s default mode of performing NDP proxying. Effectively, LXD will configure OVN to directly respond to ARP/NDP on the INFRA-UPLINK VLAN as if the gateway itself was holding the address being reached. This is a nice trick which works well at pretty small scale. But it relies on LXD configuring a static entry for every single address in the subnet. So that’s fine for a few addresses but not so much when you’re talking a /64 IPv6 subnet.
You add static routing rules to your routers. Basically you run lxc network show some-name and look for the IPv4 and IPv6 addresses that the network got assigned, then you go on your routers and you configure static routes for all the addresses that need to be sent to that OVN gateway. It works, but it’s pretty manual and effectively prevents you from delegating network creation to anyone who’s not the network admin too.
You use dynamic routing to have all public subnets and addresses configured on LXD to be advertised to the routers with the correct next-hop address. With this, there is no need to configure anything manually, keeping the OVN config very simple and allowing any user of the cluster to create their own networks and get connectivity.
Naturally I went with the last one. At the time, there was no way to do that through LXD, so I made my own by writing lxd-bgp. This is a pretty simple piece of software which uses the LXD API to inspect its networks, determine all OVN networks tied to a particular uplink network (INFRA-UPLINK in my case) and then inspect all instances running on that network.
It then sends announcements both for the subnets backing each OVN networks as well as for specific routes/addresses that are routed on top of that to specific instances running on the local system.
The result is that when an instance with a static IPv4 and IPv6 starts, the lxd-bgp instance running on that particular system will send an announcement for those addresses and traffic will start flowing.
Now deploy the same service on 3 servers, put them into 3 different LXD networks and set the exact same static IPv4 and IPv6 addresses on them and you now have a working anycast service. When one of the containers or its host go down for some reason, that route announcement goes away and the traffic now heads to the remaining instances. That does a good job at some simplistic load-balancing and provides pretty solid service availability!
The past 6 months
Now that we’ve covered the network setup I’m running, let’s spend a bit of time going over what happened over the past 6 months!
In short, well, not a whole lot. Things have pretty much just been working. The servers were installed in the datacenter on the 21st of December. I’ve then been busy migrating services from my old server at OVH over to the new cluster, finalizing that migration at the end of April.
I’ve gotten into the habit of doing a full reboot of the entire cluster every week and developed a bit of tooling for this called lxd-evacuate. This makes it easy to relocate any instance which isn’t already highly available, emptying a specific machine and then letting me reboot it. By and large this has been working great and it’s always nice to have confidence that should something happen, you know all the machines will boot up properly!
These days, I’m running 63 instances across 9 projects and a dozen networks. I spent a bit of time building up a Grafana dashboard which tracks and alerts on my network consumption (WAN port, uplink to servers and mesh), monitors the health of my servers (fan speeds, temperature, …), tracks CEPH consumption and performance, monitors the CPU, RAM and load of each of the servers and also track performance on my top services (NSD, unbound and HAProxy).
LXD also rolled out support for network ACLs somewhat recently, allowing for proper stateful firewalling directly through LXD and implemented in OVN. It took some time to setup all those ACLs for all instances and networks but that’s now all done and makes me feel a whole lot better about service security!
What’s next
On the LXD front, I’m excited about a few things we’re doing over the next few months which will make environments like mine just that much nicer:
Native BGP support (no more lxd-bgp)
Native cluster server evacuation (no more lxd-evacuate)
Built-in DNS server for instance forward/reverse records as well as DNS zones tied to networks
Built-in metrics (prometheus) endpoint exposing CPU/memory/disk/network usage of all local instances
This will let me deprecate some of those side projects I had to start as part of this work, will reduce the amount of manual labor involved in setting up all the DNS records and will give me much better insight on what’s consuming resources on the cluster.
I’m also in the process of securing my own ASN and address space through ARIN, mostly because that seemed like a fun thing to do and will give me a tiny bit more flexibility too (not to mention let me consolidate a whole bunch of subnets). So soon enough, I expect to have to deal with quite a bit of re-addressing, but I’m sure it will be a fun and interesting experience!
The previous post went over the planned redundancy aspect of this setup at the storage, networking and control plane level. Now let’s see how to get those systems installed and configured for this setup.
Firmware updates and configuration
First thing first, whether its systems coming from an eBay seller or straight from the factory, the first step is always to update all firmware to the latest available.
In my case, that meant updating the SuperMicro BMC firmware and then the BIOS/UEFI firmware too. Once done, perform a factory reset of both the BMC and UEFI config and then go through the configuration to get something that suits your needs.
The main things I had to tweak other than the usual network settings and accounts were:
Switch the firmware to UEFI only and enable Secure Boot This involves flipping all option ROMs to EFI, disabling CSM and enabling Secure Boot using the default keys.
Enable SR-IOV/IOMMU support Useful if you ever want to use SR-IOV or PCI device passthrough.
Disable unused devices In my case, the only storage backplane is connected to a SAS controller with nothing plugged into the SATA controller, so I disabled it.
Tweak storage drive classification The firmware allows configuring if a drive is HDD or SSD, presumably to control spin up on boot.
Base OS install
With that done, I grabbed the Ubuntu 20.04.1 LTS server ISO, dumped it onto a USB stick and booted the servers from it.
I had all servers and their BMCs connected to my existing lab network to make things easy for the initial setup, it’s easier to do complex network configuration after the initial installation.
The main thing to get right at this step is the basic partitioning for your OS drive. My original plan was to carve off some space from the NVME drive for the OS, unfortunately after an initial installation done that way, I realized that my motherboard doesn’t support NVME booting so ended up reinstalling, this time carving out some space from the SATA SSD instead.
In my case, I ended up creating a 35GB root partition (ext4) and 4GB swap partition, leaving the rest of the 2TB drive unpartitioned for later use by Ceph.
With the install done, make sure you can SSH into the system, also check that you can access the console through the BMC both through VGA and through the IPMI text console. That last part can be done by dumping a file in /etc/default/grub.d/ that looks like:
Finally you’ll want to make sure you apply any pending updates and reboot, then check dmesg for anything suspicious coming from the kernel. Better catch compatibility and hardware issues early on.
Networking setup
On the networking front you may remember I’ve gotten configs with 6 NICs, two gigabit ports and four 10gbit ports. The gigabit NICs are bonded together and go to the switch, the 10gbit ports are used to create a mesh with each server using a two ports bond to the others.
Combined with the dedicated BMC ports, this ends up looking like this:
Here we can see the switch receiving its uplink over LC fiber, each server has its BMC plugged into a separate switch port and VLAN (green cables), each server is also connected to the switch with a two port bond (black cables) and each server is connected to the other two using a two port bond (blue cables).
Ubuntu uses Netplan for its network configuration these days, the configuration on those servers looks something like this:
That’s the part which is common to all servers, then on top of that, each server needs its own tiny bit of config to setup the right routes to its other two peers, this looks like this:
network:
version: 2
bonds:
# server 2
bond-mesh01:
addresses:
- 2602:XXXX:Y:ZZZ::101/64
routes:
- to: 2602:XXXX:Y:ZZZ::100/128
via: fe80::ec7c:7eff:fe69:55fa
# server 3
bond-mesh02:
addresses:
- 2602:XXXX:Y:ZZZ::101/64
routes:
- to: 2602:XXXX:Y:ZZZ::102/128
via: fe80::8cd6:b3ff:fe53:7cc
bridges:
br-hosts:
addresses:
- 2602:XXXX:Y:ZZZ::101/64
My setup is pretty much entirely IPv6 except for a tiny bit of IPv4 for some specific services so that’s why everything above very much relies on IPv6 addressing, but the same could certainly be done using IPv4 instead.
With this setup, I have a 2Gbit/s bond to the top of the rack switch configured to use static addressing but using the gateway provided through IPv6 router advertisements. I then have a first 20Gbit/s bond to the second server with a static route for its IP and then another identical bond to the third server.
This allows all three servers to communicate at 20Gbit/s and then at 2Gbit/s to the outside world. The fast links will almost exclusively be carrying Ceph, OVN and LXD internal traffic, the kind of traffic that’s using a lot of bandwidth and requires good latency.
To complete the network setup, OVN is installed using the ovn-central and ovn-host packages from Ubuntu and then configured to communicate using the internal mesh subnet.
This part is done by editing /etc/default/ovn-central on all 3 systems and updating OVN_CTL_OPTS to pass a number of additional parameters:
--db-nb-addr to the local address
--db-sb-addr to the local address
--db-nb-cluster-local-addr to the local address
--db-sb-cluster-local-addr to the local address
--db-nb-cluster-remote-addr to the first server’s address
--db-sb-cluster-remote-addr to the first server’s address
--ovn-northd-nb-db to all the addresses (port 6641)
--ovn-northd-sb-db to all the addresses (port 6642)
The first server shouldn’t have the remote-addr ones set as it’s the bootstrap server, the others will then join that initial server and join the cluster at which point that startup argument isn’t needed anymore (but it doesn’t really hurt to keep it in the config).
If OVN was running unclustered, you’ll want to reset it by wiping /var/lib/ovn and restarting ovn-central.service.
Storage setup
On the storage side, I won’t go over how to get a three nodes Ceph cluster, there are many different ways to achieve that using just about every deployment/configuration management tool in existence as well as upstream’s own ceph-deploy tool.
In short, the first step is to deploy a Ceph monitor (ceph-mon) per server, followed by a Ceph manager (ceph-mgr) and a Ceph metadata server (ceph-mds). With that done, one Ceph OSD (ceph-osd) per drive needs to be setup. In my case, both the HDDs and the NVME SSD are consumed in full for this while for the SATA SSD I created a partition using the remaining space from the installation and put that into Ceph.
At that stage, you may want to learn about Ceph crush maps and do any tweaking that you want based on your storage setup.
In my case, I have two custom crush rules, one which targets exclusively HDDs and one which targets exclusively SSDs. I’ve also made sure that each drive has the proper device class and I’ve tweaked the affinity a bit such that the faster drives will be prioritized for the first replica.
I’ve also created an initial ceph fs filesystem for use by LXD with:
ceph osd pool create lxd-cephfs_metadata 32 32 replicated replicated_rule_ssd
ceph osd pool create lxd-cephfs_data 32 32 replicated replicated_rule_hdd
ceph fs new lxd-cephfs lxd-cephfs_metadata lxd-cephfs_data
ceph fs set lxd-cephfs allow_new_snaps true
This makes use of those custom rules, putting the metadata on SSD with the actual data on HDD.
The cluster should then look something a bit like that:
root@langara:~# ceph osd tree
ID CLASS WEIGHT TYPE NAME STATUS REWEIGHT PRI-AFF
-1 34.02979 root default
-3 11.34326 host abydos
4 hdd 3.63869 osd.4 up 1.00000 0.12500
7 hdd 5.45799 osd.7 up 1.00000 0.25000
0 ssd 0.46579 osd.0 up 1.00000 1.00000
10 ssd 1.78079 osd.10 up 1.00000 0.75000
-5 11.34326 host langara
5 hdd 3.63869 osd.5 up 1.00000 0.12500
8 hdd 5.45799 osd.8 up 1.00000 0.25000
1 ssd 0.46579 osd.1 up 1.00000 1.00000
11 ssd 1.78079 osd.11 up 1.00000 0.75000
-7 11.34326 host orilla
3 hdd 3.63869 osd.3 up 1.00000 0.12500
6 hdd 5.45799 osd.6 up 1.00000 0.25000
2 ssd 0.46579 osd.2 up 1.00000 1.00000
9 ssd 1.78079 osd.9 up 1.00000 0.75000
LXD setup
The last piece is building up a LXD cluster which will then be configured to consume both the OVN networking and Ceph storage.
For OVN support, using an LTS branch of LXD won’t work as 4.0 LTS predates OVN support, so instead I’ll be using the latest stable release.
Installation is as simple as: snap install lxd --channel=latest/stable
Then on run lxd init on the first server, answer yes to the clustering question, make sure the hostname is correct and that the address used is that on the mesh subnet, then create the new cluster setting an initial password and skipping over all the storage and network questions, it’s easier to configure those by hand later on.
After that, run lxd init on the remaining two servers, this time pointing them to the first server to join the existing cluster.
In my case, I’ve also setup a lxd-hdd pool, resulting in a final setup of:
root@langara:~# lxc storage list
+--------+-------------+--------+---------+---------+
| NAME | DESCRIPTION | DRIVER | STATE | USED BY |
+--------+-------------+--------+---------+---------+
| hdd | | ceph | CREATED | 1 |
+--------+-------------+--------+---------+---------+
| shared | | cephfs | CREATED | 0 |
+--------+-------------+--------+---------+---------+
| ssd | | ceph | CREATED | 16 |
+--------+-------------+--------+---------+---------+
Up next
The next post is likely to be quite network heavy, going into why I’m using dynamic routing and how I’ve got it all setup. This is the missing piece of the puzzle in what I’ve shown so far as without it, you’d need an external router with a bunch of static routes to send traffic to the OVN networks.
In the previous post I went over the reasons for switching to my own hardware and what hardware I ended up selecting for the job.
Now it’s time to look at how I intend to achieve the high availability goals of this setup. Effectively limiting the number of single point of failure as much as possible.
Hardware redundancy
On the hardware front, every server has:
Two power supplies
Hot swappable storage
6 network ports served by 3 separate cards
BMC (IPMI/redfish) for remote monitoring and control
The switch is the only real single point of failure on the hardware side of things. But it also has two power supplies and hot swappable fans. If this ever becomes a problem, I can also source a second unit and use data and power stacking along with MLAG to get rid of this single point of failure.
I mentioned that each server has four 10Gbit ports yet my switch is Gigabit. This is fine as I’ll be using a mesh type configuration for the high-throughput part of the setup. Effectively connecting each server to the other two with a dual 10Gbit bond each. Then each server will get a dual Gigabit bond to the switch for external connectivity.
Software redundancy
The software side is where things get really interesting, there are three main aspects that need to be addressed:
Storage
Networking
Compute
Storage
For storage, the plan is to rely on Ceph, each server will run a total of 4 OSDs, one per physical drive with the SATA SSD acting as boot drive too with the OSD being a large partition on it instead of the full disk.
Each server will also act as MON, MGR and MDS providing a fully redundant Ceph cluster on 3 machines capable of providing both block and filesystem storage through RBD and FS.
Two maps will be setup, one for HDD storage and one for SSD storage. Storage affinity will also be configured such that the NVME drives will be used for the primary replica in the SSD map with the SATA drives holding secondary/tertiary replicas instead.
This makes the storage layer quite reliable. A full server can go down with only minimal impact. Should a server being offline be caused by hardware failure, the on-site staff can very easily relocate the drives from the failed server to the other two servers allowing Ceph to recover the majority of its OSDs until the defective server can be repaired.
Networking
Networking is where things get quite complex when you want something really highly available. I’ll be getting a Gigabit internet drop from the co-location facility on top of which a /27 IPv4 and a /48 IPv6 subnet will be routed.
Internally, I’ll be running many small networks grouping services together. None of those networks will have much in the way of allowed ingress/egress traffic and the majority of them will be IPv6 only.
The majority of egress will be done through a proxy server and IPv4 access will be handled through a DNS64/NAT64 setup. Ingress when needed will be done by directly routing an additional IPv4 or IPv6 address to the instance running the external service.
At the core of all this will be OVN which will run on all 3 machines with its database clustered. Similar to Ceph for storage, this allows machines to go down with no impact on the virtual networks.
Where things get tricky is on providing a highly available uplink network for OVN. OVN draws addresses from that uplink network for its virtual routers and routes egress traffic through the default gateway on that network.
One option would be for a static setup, have the switch act as the gateway on the uplink network, feed that to OVN over a VLAN and then add manual static routes for every public subnet or public address which needs routing to a virtual network. That’s easy to setup, but I don’t like the need to constantly update static routing information in my switch.
Another option is to use LXD’s l2proxy mode for OVN, this effectively makes OVN respond to ARP/NDP for any address it’s responsible for but then requires the entire IPv4 and IPv6 subnet to be directly routed to the one uplink subnet. This can get very noisy and just doesn’t scale well with large subnets.
The more complicated but more flexible option is to use dynamic routing. Dynamic routing involves routers talking to each other, advertising and receiving routes. That’s the core of how the internet works but can also be used for internal networking.
My setup effectively looks like this:
Three containers running FRR each connected to both the direct link with the internet provider and to the OVN uplink network.
Each one of those will maintain BGP sessions with the internet provider’s routers AS WELL as with the internal hosts running OVN.
VRRP is used to provide a single highly available gateway address on the OVN uplink network.
I wrote lxd-bgp as a small BGP daemon that integrates with the LXD API to extract all the OVN subnets and instance addresses which need to be publicly available and announces those routes to the three routers.
This may feel overly complex and it quite possibly is, but that gives me three routers, one on each server and only one of which need to be running at any one time. It also gives me the ability to balance routing traffic both ingress or egress by tweaking the BGP or VRRP priorities.
The nice side effect of this setup is that I’m also able to use anycast for critical services both internally and externally. Effectively running three identical copies of the service, one per server, all with the exact same address. The routers will be aware of all three and will pick one at the destination. If that instance or server goes down, the route disappears and the traffic goes to one of the other two!
Compute
On the compute side, I’m obviously going to be using LXD with the majority of services running in containers and with a few more running in virtual machines.
Stateless services that I want to always be running no matter what happens will be using anycast as shown above. This also applies to critical internal services as is the case above with my internal DNS resolvers (unbound).
Other services may still run two or more instances and be placed behind a load balancing proxy (HAProxy) to spread the load as needed and handle failures.
Lastly even services that will only be run by a single instance will still benefit from the highly available environment. All their data will be stored on Ceph, meaning that in the event of a server maintenance or failure, it’s a simple matter of running lxc move to relocate them to any of the others and bring them back online. When planned ahead of time, this is service downtime of less than 5s or so.
Up next
In the next post, I’ll be going into more details on the host setup, setting up Ubuntu 20.04 LTS, Ceph, OVN and LXD for such a cluster.
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