More fun with etcd-compute

Last time I ended my work getting etcd-compute running at the point where I needed to configure the virtual networking. I’ve been busy the past few days with meetings and other work-related stuff, so it’s taken me a while to continue on this experiment. But I have some time now; let’s jump back in!

The reason I thought that I needed to set up virtual networking was that when I ran ip a on my controller node, all I had was the loopback and main ethernet interfaces. The directions for etcd-compute talked about setting up the metadata server by adding the IP address it uses to a virtual bridge: sudo ip addr add 169.254.169.254 dev virbr0. As I didn’t have such a bridge on my VM, I figured I had to add it. I tried sever guides on adding a bridge to an Ubuntu server, but each one ended up messing up the networking, making the VM unreachable. I ended up re-creating my etcd1 so many times that I gave up and figured I try without the metadata server. I started the placement and etcd servers by running docker.sh, and then just on a lark I re-ran ip a. This time it showed:

ed@etcd1:~$ ip a
1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: ens3: mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether fa:16:3e:90:6d:d0 brd ff:ff:ff:ff:ff:ff
inet 9.114.111.201/24 brd 9.114.111.255 scope global ens3
valid_lft forever preferred_lft forever
inet6 fe80::f816:3eff:fe90:6dd0/64 scope link
valid_lft forever preferred_lft forever
3: virbr0: mtu 1500 qdisc noqueue state DOWN group default qlen 1000
link/ether 52:54:00:35:c1:0d brd ff:ff:ff:ff:ff:ff
inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
valid_lft forever preferred_lft forever
4: virbr0-nic: mtu 1500 qdisc fq_codel master virbr0 state DOWN group default qlen 1000
link/ether 52:54:00:35:c1:0d brd ff:ff:ff:ff:ff:ff

I’m not sure how those entries for ‘virbr0’ and ‘virbr0-nic’ got added (maybe docker added them?), but I wasn’t going to worry about that! So I ran the following commands, and they worked without a problem:

sudo ip addr add 169.254.169.254 dev virbr
sudo python md_server/mdserver/server.py mdserver.conf &

So now that the metadata server is running, time to try running ecompute on all the nodes. I use iTerm2, which has some sweet tools for splitting the terminal screen and running the same command in the different panes. I recorded a script of what happened:

I ran the command ecompute & on all the nodes to start the compute service in the background.

ed@etcd1:~/projects/etcd-compute(master)$ ecompute &
[1] 4661
ed@etcd1:~/projects/etcd-compute(master)$ 1556230694.3633301: PID: 4661 [None] {'uuid': '19a89e30-4bdd-49e7-b1a0-d4172bf7b289', 'placement': {'endpoint': 'http://etcd1:8080'}, 'etcd': {'host': 'etcd1'}, 'resize': False, 'bridge': 'br0'}
1556230694.364856: PID: 4661 [19a89e30-4bdd-49e7-b1a0-d4172bf7b289] {'VCPU': 4, 'DISK_GB': 77, 'MEMORY_MB': 7976}
1556230694.5012665: PID: 4661 [19a89e30-4bdd-49e7-b1a0-d4172bf7b289] Existing resource provider with gen 7 found with usages: VCPU: 0, MEMORY_MB: 0, DISK_GB: 0.

It’s interesting to see that because I had run this a few times earlier, etcd-compute recognized the UUID of the node, and noted that there was already an entry for that resource provider, with a generation of 7. If I were to stop that ecompute service and then re-start it, I would see the same as above, except this time the generation would be 8. That’s because when the service is killed, it changes the ‘reserved’ amount of its VCPU inventrory to the total amount, effectively preventing that node from being provisioned. That change increments the resource provider’s generation.

At about the 30-second mark, I tried to create a VM by running the command eschedule 'resources=VCPU:1,DISK_GB:1,MEMORY_MB:256' on the etcd3 node. That worked, and almost immediately you can see that it was scheduled to the etcd1 node, and the build process starts. However, there were many errors output, with the main one being error: failed to get domain ‘ff77fe58-e96a-498b-a3f5-a59030987238’. This is repeated several times, along with a bunch of network errors. So at this point I stopped the experiment.

There’s a lot I learned by going through all this, and I see many places where the etcd-compute project could be improved, starting with the documentation. I’d also like to get some less ethereal debugging output, so that when there are problems like I had spinning up a VM, they are recorded for later analysis. I’d also like to learn a lot more about the details of the networking required so that I can make sense of some of the networking errors.

The author of etcd-compute, Chris Dent, and I are hoping to have a mini-sprint on this project next week at the Open Infrastructure Summit in Denver, Colorado. If you will be there and want to join in the fun, drop me an email and I’ll let you know when we settle on a time and place.

One thought on “More fun with etcd-compute”

  1. This points out a couple (more) things I failed to explain well in the README. In this case the meanings of the various nodes/hosts that are involved. ecompute is a virt host. eschedule runs anywhere you want as long as it knows how to talk to the two containers. And the containers run wherever is convenient. When I first started the work they were all the same host but as my testing continued it turned into 3+N, to make sure the networked interactions were behaving.

    The repeated “domain not found” errors are the result of a loop in which the ecompute is querying libvirt for IP information. It’s probably overly verbose and should only report when the loop completely fails, instead of each iteration.

    One relatively simple and reasonable fix would be for both ecompute and eschedule to use real loggging instead of my hacked up print statements.

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