Tag Archives: mclu

Mini Cloud/Cluster v2.0

Last year I wrote and rewrote a little command line tool for managing my virtualization cluster.

Of course I could use OpenStack RDO but OpenStack is a vast box of somewhat working bits and pieces. I think for a small cluster like mine you can get the essential functionality of OpenStack a lot more simply — in 1300 lines of code as it turns out.

The first thing that small cluster management software doesn’t need is any permanent daemon running on the nodes. The reason is that we already have sshd (for secure management access) and libvirtd (to manage the guests) out of the box. That’s quite sufficient to manage all the state we care about. My Mini Cloud/Cluster software just goes out and queries each node for that information whenever it needs it (in parallel of course). Nodes that are switched off are handled by ignoring them.

The second thing is that for a small cloud we can toss features that aren’t needed at all: multi-user/multi-tenant, failover, VLANs, a nice GUI.

The old mclu (Mini Cluster) v1.0 was written in Python and used Ansible to query nodes. If you’re not familiar with Ansible, it’s basically parallel ssh on steroids. This was convenient to get the implementation working, but I ended up rewriting this essential feature of Ansible in ~ 60 lines of code.

The huge down-side of Python is that even such a small program has loads of hidden bugs, because there’s no safety at all. The rewrite (in OCaml) is 1,300 lines of code, so a fraction larger, but I have a far higher confidence that it is mostly bug free.

I also changed around the way the software works to make it more “cloud like” (and hence the name change from “Mini Cluster” to “Mini Cloud”). Guests are now created from templates using virt-builder, and are stateless “cattle” (although you can mix in “pets” and mclu will manage those perfectly well because all it’s doing is remote libvirt-over-ssh commands).

$ mclu status
ham0                     on
                           total: 8pcpus 15.2G
                            used: 8vcpus 8.0G by 2 guest(s)
                            free: 6.2G
ham1                     on
                           total: 8pcpus 15.2G
                            free: 14.2G
ham2                     on
                           total: 8pcpus 30.9G
                            free: 29.9G
ham3                     off

You can grab mclu v2.0 from the git repository.

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Mini-cluster (mclu) rewritten to use ansible

As (kind of) requested in several comments on the previous post I’ve rewritten mclu so it uses Ansible for most communications. (diff)

Since Ansible handles communicating with ssh servers in parallel, it’s a bit faster and in theory a bit more scalable.

Update

Another advantage is that you can run regular ansible commands, for example:

ansible cluster -u root -a "yum -y update"

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Mini-cluster (mclu) command line tool

After setting up my virtualization cluster I was disappointed by the available cluster management tools. You can either “go large” (Openstack) with all the associated trauma of setting that up, or go with various GUIs. Or you can run ssh & virsh commands, which gets tedious quickly.

Therefore I wrote some simple scripts to help perform common cluster operations on small clusters (up to about 10 nodes). It’s only 1000 lines of code, and the advantage is you only need sshd and libvirtd on each node, which you almost certainly have already.

You can download them from this git repository.

Get cluster status:

$ mclu status
ham0 (ham0.home.annexia.org) down
ham1 (ham1.home.annexia.org) down
ham2 (ham2.home.annexia.org) down
ham3 (ham3.home.annexia.org) down
$ mclu wake --all
$ mclu status
ham0 (ham0.home.annexia.org) up ssh: OK libvirt: OK
ham1 (ham1.home.annexia.org) up ssh: OK libvirt: OK
ham2 (ham2.home.annexia.org) up ssh: OK libvirt: OK
ham3 (ham3.home.annexia.org) up ssh: OK libvirt: OK

Build a new VM (using virt-builder):

$ mclu build --size=20G -- \
   ham0:tmp-f20-1 fedora-20 \
   --root-password password:123456

List running VMs, live-migrate the new one around:

Note that wildcards can be used when starting, stopping and migrating VMs:

$ mclu list
ham0:tmp-f20-1	running
$ mclu migrate \* ham2:
$ mclu list
ham2:tmp-f20-1	running
$ mclu stop ham2:*
$ mclu list
tmp-f20-1	inactive

Open a console

$ mclu start ham3:tmp-f20-1
$ mclu console tmp-f20-1
Connected to domain tmp-f20-1
Escape character is ^]
^]
$ mclu viewer tmp-f20-1
(graphical window opens)

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