3 ms·

I'm doing a bit of a simplification here so please someone correct me if I'm not saying this correctly Every single instance of a VM has its own Kernel. When a

I'm doing a bit of a simplification here so please someone correct me if I'm not saying this correctly Every single instance of a VM has its own Kernel. When a VM boots up, it gets allocated a portion of hardware and boots up a kernel and allocates memory to itself. VMs each are isolated from each other in that they don't share resources and each VM is free to do whatever it wants to do with the hardware it is given. Like you said, to the host machine, that hardware is no longer available for any other VM to use. For Containers, they all live on a SINGLE kernel. They share resources across each other and the Kernel handles the multiple processes much like it would handle any other multithreaded process. If you have 3 VMs that all require a specific set of resources to run an application, you need 3x that hardware. This is not true for containers. You can get away with less because the containers will share the resources that the kernel as access to. I call them "lower level" in the sense that they do so much less than VMs. You CAN use containers as a VM in that a container can boot an entire Kernel, but generally you don't do this.

user5994461 10y ago
VMs share resources from the host: disk, network, memory. Just like a container shares resources from the host. Containers re-use the running Operating System from the host, it saves memory but it can only run a single OS. A VM can run any operating system, and each VM runs its OS independently. VMs are memory intensive, there is a base 100-500MB to pay to run any VM because of the independent OS. (Note that the advanced VM managers have evolved to have memory deduplication and COW across VMs.) Containers exist to save memory. That was the critical pain at the time they came to existence. Memory was expensive, it was a major problem when you wanted to run 10 hello world applications as 10 separate VMs.
- ec109685 10y ago
  Containers give the OS the ability to optimally schedule processes among them. VMs are black boxes to the hypervisor, limiting its ability to optimize.
  - user5994461 10y ago
    The hypervisor has processes inside the VMs. It has limited control but it is far from blind.

user5994461 10y ago

VMs share resources from the host: disk, network, memory. Just like a container shares resources from the host. Containers re-use the running Operating System from the host, it saves memory but it can only run a single OS. A VM can run any operating system, and each VM runs its OS independently. VMs are memory intensive, there is a base 100-500MB to pay to run any VM because of the independent OS. (Note that the advanced VM managers have evolved to have memory deduplication and COW across VMs.) Containers exist to save memory. That was the critical pain at the time they came to existence. Memory was expensive, it was a major problem when you wanted to run 10 hello world applications as 10 separate VMs.

ec109685 10y ago
Containers give the OS the ability to optimally schedule processes among them. VMs are black boxes to the hypervisor, limiting its ability to optimize.
- user5994461 10y ago
  The hypervisor has processes inside the VMs. It has limited control but it is far from blind.