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> At the minimum, renting an instance in AWS or GCE is equivalent to renting a physical server. Applications don't care what's the brand of the server they're r

by zeroxfe 10y ago

> At the minimum, renting an instance in AWS or GCE is equivalent to renting a physical server. Applications don't care what's the brand of the server they're running on. This frequently trips people up. Cloud instances (typically) have far lower availability than physical servers. They also have no (cheap) persistence across VM evictions. Prepare for an unpleasant surprise if you're blindly migrating applications from physical servers to cloud instances.

williamstein 10y ago
> This frequently trips people up. Cloud instances (typically) have far lower availability than physical servers. They also have no (cheap) persistence across VM evictions. This may be true for AWS but (in my experience since 2014) it is not true for Google compute engine. On GCE, VM instances automatically migrate when the host is rebooted, and VM availability and uptime is impressive. Also, on GCE, the default recommended disks are all persistent, since they are block devices mounted over the network; this wasn't the case years ago, but is now, and it is very impressive. Disclaimer: my startup is in the Google startup program.
- zeroxfe 10y ago
  Yep. GCE VM migration and persistent storage is really amazing, and getting better with every release, however there are still limitations and caveats that can get you in trouble (especially if you have very tight latency requirements.) Glad you like it! Good luck with your startup. Disclaimer: I work on infrastructure systems at Google :-)
user5994461 10y ago
> Cloud instances (typically) have far lower availability than physical servers. This is common belief that is just plain wrong. Servers can stay online for years without issues, same things on AWS and physical servers. > They also have no (cheap) persistence across VM evictions. I don't even understand that this sentence mean. You can start by explaining what is "VM eviction"? Whatever it is. Physical servers have no soft of failover or persistence for when one server suddenly dies. People started migrating from physical servers to virtualized more than 10 years ago (i.e. VmWare). AWS/GCE are not fundamentally different.
- drieddust 10y ago
  > Servers can stay online for years without issues, same things on AWS and physical servers Why they don't back it up SLA promise then? Having a VM does not guarantee increased uptime. On premises virtualization can guarantee it,cloud cannot.
- 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 ago
    What 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 ago
      In 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)

by zeroxfe 10y ago

williamstein 10y ago

> This frequently trips people up. Cloud instances (typically) have far lower availability than physical servers. They also have no (cheap) persistence across VM evictions. This may be true for AWS but (in my experience since 2014) it is not true for Google compute engine. On GCE, VM instances automatically migrate when the host is rebooted, and VM availability and uptime is impressive. Also, on GCE, the default recommended disks are all persistent, since they are block devices mounted over the network; this wasn't the case years ago, but is now, and it is very impressive. Disclaimer: my startup is in the Google startup program.

zeroxfe 10y ago
Yep. GCE VM migration and persistent storage is really amazing, and getting better with every release, however there are still limitations and caveats that can get you in trouble (especially if you have very tight latency requirements.) Glad you like it! Good luck with your startup. Disclaimer: I work on infrastructure systems at Google :-)

user5994461 10y ago

> Cloud instances (typically) have far lower availability than physical servers. This is common belief that is just plain wrong. Servers can stay online for years without issues, same things on AWS and physical servers. > They also have no (cheap) persistence across VM evictions. I don't even understand that this sentence mean. You can start by explaining what is "VM eviction"? Whatever it is. Physical servers have no soft of failover or persistence for when one server suddenly dies. People started migrating from physical servers to virtualized more than 10 years ago (i.e. VmWare). AWS/GCE are not fundamentally different.

drieddust 10y ago
> Servers can stay online for years without issues, same things on AWS and physical servers Why they don't back it up SLA promise then? Having a VM does not guarantee increased uptime. On premises virtualization can guarantee it,cloud cannot.
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 ago
  What 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 ago
    In 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)