Except for UPS instance types, the cloud systems do not and will not have battery or generator backup, if we lose power that’s too bad. Individual physical nodes are single points of failure for the virtual instances running on them, at this point it is left as an exercise for the user to implement HA Clustering across multiple VMs or to monitor their services and restart them if they fail. If your system is a single VM and is not fault tolerant be sure to use one of the ups instance types.
OpenStack requires the use of predefined “Instance Types” also referred to as “Flavors”. These define the virtual hardware including number of cpus, memory size, size of the root disk and optionally additional ephemeral disk space. We’ve defined instance types using the following scheme:
- s1.<N>core - N cores, N x 512m RAM, 10G root disk
- m1.<N>core - N cores, N x 1024m RAM, 16G root disk
- lg.<N>core - N cores, N x 2048m RAM, 32G root disk
- xl.<N>core - N cores, N x 4096m RAM, 64G root disk
These standard types run on cluster nodes without redundant components and without UPS power and are best suited to tasks where the uptime of an individual component is not critical such as compute nodes or worker nodes behind a load balancer (see LBaaS section).
There’s one special flavor for instances launched specifically for creating image snapshots:
- for.snapshot - 2 cores, 4096M RAM, 0G root disk
For a fixed total amount of resources, a greater number of smaller instances (say a few cores and a few GB of RAM each) will be easier to pack onto the available host machines than a smaller number of larger instances (tens of cores or tens of GB of RAM).
Obviously it’s not really 0G, that is magic for whatever the minimum size of the base image is. This is ideal for making snapshots as you want them to be as small as possible.
We also provide a selection of instance types that run on a (much) smaller pool or less performant but more redundant hardware (including UPS and Generator backed power, redundant power supplies and mirrored hard drives). This is the same configuration used by TIG for hosting our virtualized services on OpenStack such as http://people.csail.mit.edu. These instance types all have 32G root disks with the number of cores © and gigabytes of RAM (g) encoded in the name:
It is possible to create custom instance types for specific projects, so your project may have extra types available, ask someone in your group why that is and what they are for. If you need a custom size created email firstname.lastname@example.org.
See also Launching a VM