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Tuesday, May 18th, 2010 | Author:

eth0Some friends told me for a while about collectd, why I should look at it, why munin is so painful and so on. If you’ve been reading my posts you know I have tweaked a little my $WORK munin install to make it faster and lighter. But I finally took time to explore collectd, and I regret to not have done this before. It has so many pros that I decided to implement it in parallel with munin (because I can’t afford being blind on metrics). But collectd comes without an UI : it “only” collectds data, but that’s not a problem. There are various web interfaces and after giving a look to a bunch of them I fell in love with Lindsay Holmwood‘s Visage.

This piece of software is definitely cool : all graphs are rendered live in your browser in SVG. Yes ! Realtime graphs, no need for crappy flash s***, zoom. It is based on sinatra, haml and some JS libraries (I won’t talk about this, my JS foo is deeper than the Mariana Trench). But it lacked some features : it’s OK when you have a few hosts but when the hosts list starts being loooong then the interface needs some improvements. So I forked it on github and implemented (some parts of) what I needed. My github fork has host grouping & per host profiles. Check this out and enjoy Visage !

Now working on sets of graphs :)

PS : <3 Guigui2

Category: BOFH Life, Code, NetAdmin, SysAdmin, Tech  | Tags: , , ,  | Comments off
Wednesday, April 14th, 2010 | Author:

eth0I already blogged about my experiments with mcollective & xen but I had something a little bigger in my mind. A friend had sent me a video showing some vmware neat features (DRS mainly) with VMs migrating through hypervisors automatically.

So I wrote a “proof of concept” of what you can do with an awesome tool like mcollective. The setup of this funny game is the following :

  • 1 box used a iSCSI target that serves volumes to the world
  • 2 xen hypervisors (lenny packages) using open-iscsi iSCSI initiator to connect to the target. VMs are stored in LVM, nothing fancy

The 3 boxens are connected on a 100Mb network and the hypervisors have an additionnal gigabit network card with a crossover cable to link them (yes, this is a lab setup). You can find a live migration howto here.

For the mcollective part I used my Xen agent (slightly modified from the previous post to support migration), which is based on my xen gem. The client is the largest part of the work but it’s still less than 200 lines of code. It can (and will) be improved because all the config is hardcoded. It would also deserve a little DSL to be able to handle more “logic” than “if load is superior to foo” but as I said before, it’s a proof of concept.

Let’s see it in action :

hypervisor2:~# xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0   233     2     r-----    873.5
hypervisor3:~# xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0   232     2     r-----  78838.0
test1                                        6   256     1     -b----     18.4
test2                                        4   256     1     -b----     19.3
test3                                       20   256     1     r-----     11.9

test3 is a VM that is “artificially” loaded, as is the machine “hypervisor3” (to trigger migration)

[mordor:~] ./mc-xen-balancer
[+] hypervisor2 : 0.0 load and 0 slice(s) running
[+] init/reset load counter for hypervisor2
[+] hypervisor2 has no slices consuming CPU time
[+] hypervisor3 : 1.11 load and 3 slice(s) running
[+] added test1 on hypervisor3 with 0 CPU time (registered 18.4 as a reference)
[+] added test2 on hypervisor3 with 0 CPU time (registered 19.4 as a reference)
[+] added test3 on hypervisor3 with 0 CPU time (registered 18.3 as a reference)
[+] sleeping for 30 seconds

[+] hypervisor2 : 0.0 load and 0 slice(s) running
[+] init/reset load counter for hypervisor2
[+] hypervisor2 has no slices consuming CPU time
[+] hypervisor3 : 1.33 load and 3 slice(s) running
[+] updated test1 on hypervisor3 with 0.0 CPU time eaten (registered 18.4 as a reference)
[+] updated test2 on hypervisor3 with 0.0 CPU time eaten (registered 19.4 as a reference)
[+] updated test3 on hypervisor3 with 1.5 CPU time eaten (registered 19.8 as a reference)
[+] sleeping for 30 seconds

[+] hypervisor2 : 0.16 load and 0 slice(s) running
[+] init/reset load counter for hypervisor2
[+] hypervisor2 has no slices consuming CPU time
[+] hypervisor3 : 1.33 load and 3 slice(s) running
[+] updated test1 on hypervisor3 with 0.0 CPU time eaten (registered 18.4 as a reference)
[+] updated test2 on hypervisor3 with 0.0 CPU time eaten (registered 19.4 as a reference)
[+] updated test3 on hypervisor3 with 1.7 CPU time eaten (registered 21.5 as a reference)
[+] hypervisor3 has 3 threshold overload
[+] Time to see if we can migrate a VM from hypervisor3
[+] VM key : hypervisor3-test3
[+] Time consumed in a run (interval is 30s) : 1.7
[+] hypervisor2 is a candidate for being a host (step 1 : max VMs)
[+] hypervisor2 is a candidate for being a host (step 2 : max load)
trying to migrate test3 from hypervisor3 to hypervisor2 (10.0.0.2)
Successfully migrated test3 !

Let’s see our hypervisors :

hypervisor2:~# xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0   233     2     r-----    878.9
test3                                       25   256     1     -b----      1.1
hypervisor3:~# xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0   232     2     r-----  79079.3
test1                                        6   256     1     -b----     18.4
test2                                        4   256     1     -b----     19.4

A little word about configuration options :

  • interval : the poll time in seconds.  this should not be too low, let the machine some time and avoid load peeks to distort the logic.
  • load_threshold : where you consider the machine load is too high and that it is time to move some stuff away (tampered with max_over, see below)
  • daemonize : not used yet
  • max_over : maximum time (in minutes) where load should be superior to the limit. When reached, it’s time, really. Don’t set it too low and at least 2*interval or sampling will not be efficient
  • debug : well….
  • max_vm_per_host : the maximum VMs a host can handle. If a host already hit this limit it will not be candidate for receiving a VM
  • max_load_candidate : same thing as above, but for the load
  • host_mapping : a simple CSV file to handle non-DNS destinations (typically my crossover cable address have no DNS entries)

What is left to do :

  • Add some barriers to avoid migration madness to let load go down after a migration or to avoid migrating a VM permanently
  • Add a DSL to insert some more logic
  • Write a real client, not a big fat loop

Enjoy the tool !

Files :