4 ms·
> This is common belief that is just plain wrong. Sorry, you'll need to back that up. Evictions are when your VM is booted off a physical machine to a differe
by zeroxfe 10y ago
> This is common belief that is just plain wrong.
Sorry, you'll need to back that up.
Evictions are when your VM is booted off a physical machine to a different one. This usually happens when something in the the underlying infrastructure is undergoing maintenance (e.g., networking, power, kernel, physical machine, etc.)
VMs have to deal with servers dying plus evictions plus control and management plane failures, which significantly reduces the availability of a single instance. So strictly speaking, cloud instances typically have lower availability than physical machines.
> Physical servers have no soft of failover or persistence for when one server suddenly dies.
Servers suddenly dying is not the failure mode that requires persistence -- it's evictions. This is why cloud services tend to prefer external distributed storage systems to local disk, and a multitude of ways to quickly and automatically reinstall machines on instance turnup.
BTW, GCE recently started supporting VM migration (which you can opt into), where they attempt to migrate your instance to another physical machine without losing any state. There are still limitations to this, but for a lot of simple cases can work well.
- boulos 10y agoWhat do you mean recently? We've been doing this for about three years, and it was part of declaring Compute Engine as generally available. As for "limitations", I mean we can't save you if the NIC or ToR fails, but we lose VMs really rarely. Feel free to ping me internally, and I'll point you at our dashboards. Disclosure: I work on Google Cloud.
- parasubvert 10y agoIn fairness, I could launch EC2 instances as a whole about 10 years ago so the whole of GCP is recent. (Good job on it though, quality is a differentiator)
- boulos 10y agoAgreed! My issue was which word "recently" bound to (GCE or "the universe"). I interpreted it as GCE.
- zeroxfe 10y agoThanks, yes I know :-) I consider three years to be pretty recent (from the perspective of people managing their own servers.)
- user5994461 10y agoIt doesn't matter whether the application is abstracted on bare metal, on VmWare or on AWS. There's still physical hardware down the chain that calls for maintenance. When the physical hardware require maintenance everything on top is fucked or need to be moved. For planned maintenance: - If you're bare metal. You cannot migrate to a working server. - If you're virtualized, you have to stop the service and restart on another host. - If you're virtualized on GCE or vSphere datacenter, they'll migrate the VM live while it's running. GCE has supported live migrations for multiple years. VmWare supports that for about 10 years (yep, no kidding ^^) > VMs have to deal with servers dying plus evictions plus control and management plane failures, which significantly reduces the availability of a single instance. So strictly speaking, cloud instances typically have lower availability than physical machines. Bare metal servers have to deal with hardware dying plus evictions plus control and management plane failures, which significantly reduces the availability of a single server. So strictly speaking, cloud instances and physical servers are the same thing. They both live on physical hardware.