glance – Made by Mikal

A first pass at glance replication

Post author:mikal
Post published:July 11, 2012
Post category:OpenStack

A few weeks back I was tasked with turning up a new OpenStack region. This region couldn't share anything with existing regions because the plan was to test pre-release versions of OpenStack there, and if we shared something like glance then we would either have to endanger glance for all regions during testing, or not test glance. However, our users already have a favorite set of images uploaded to glance, and I really wanted to make it as easy as possible for them to use the new region -- I wanted all of their images to magically just appear there. What I needed was some form of glance replication. I'd sat in on the glance replication session at the Folsom OpenStack Design Summit. The NeCTAR use case at the bottom is exactly what I wanted, so its reassuring that other people wanted something like that too. However, no one was working on this feature. So I wrote it. In fact, because of the code review process I wrote it twice, but let's not dwell on that too much. So, as of change id I7dabbd6671ec75a0052db58312054f611707bdcf there is a very simple replicator script in glance/bin. Its not perfect, and I expect it…

Further adventures with base images in OpenStack

Post author:mikal
Post published:January 4, 2012
Post category:OpenStack

I was bored over the New Years weekend, so I figured I'd have a go at implementing image cache management as discussed previously. I actually have an implementation of about 75% of that blueprint now, but its not ready for prime time yet. The point of this post is more to document some stuff I learnt about VM startup along the way so I don't forget it later. So, you want to start a VM on a compute node. Once the scheduler has selected a node to run the VM on, the next step is the compute instance on that machine starting the VM up. First the specified disk image is fetched from your image service (in my case glance), and placed in a temporary location on disk. If the image is already a raw image, it is then renamed to the correct name in the instances/_base directory. If it isn't a raw image then it is converted to raw format, and that converted file is put in the right place. Optionally, the image can be extended to a specified size as part of this process. Then, depending on if you have copy on write (COW) images turned on or…

Openstack compute node cleanup

Post author:mikal
Post published:December 20, 2011
Post category:OpenStack

I've never used openstack before, which I imagine is similar to many other people out there. Its actually pretty cool, although I encountered a problem the other day that I think is worthy of some more documentation. Openstack runs virtual machines for users, in much the same manner as Amazon's EC2 system. These instances are started with a base image, and then copy on write is used to write differences for the instance as it changes stuff. This makes sense in a world where a given machine might be running more than one copy of the instance. However, I encountered a compute node which was running low on disk. This is because there is currently nothing which cleans up these base images, so even if none of the instances on a machine require that image, and even if the machine is experiencing disk stress, the images still hang around. There are a few blog posts out there about this, but nothing really definitive that I could find. I've filed a bug asking for the Ubuntu package to include some sort of cleanup script, and interestingly that led me to learn that there are plans for a pretty comprehensive image management…